Spatial–temporal patterns of inorganic nitrogen air … · 2020. 7. 31. · 10932 W. Xu et al.: Spatial–temporal patterns of inorganic nitrogen air concentrations and wet/bulk

Atmos Chem Phys 18 10931ndash10954 2018httpsdoiorg105194acp-18-10931-2018copy Author(s) 2018 This work is distributed underthe Creative Commons Attribution 40 License

Spatialndashtemporal patterns of inorganic nitrogen air concentrationsand deposition in eastern ChinaWen Xu12 Lei Liu3 Miaomiao Cheng4 Yuanhong Zhao5 Lin Zhang5 Yuepeng Pan6 Xiuming Zhang7 Baojing Gu8Yi Li9 Xiuying Zhang3 Jianlin Shen10 Li Lu11 Xiaosheng Luo12 Yu Zhao13 Zhaozhong Feng2Jeffrey L Collett Jr14 Fusuo Zhang1 and Xuejun Liu1

1College of Resources and Environmental Sciences Key Laboratory of Plant-Soil Interactions of MOE Beijing KeyLaboratory of Cropland Pollution Control and Remediation China Agricultural University Beijing 100193 China2State Key Laboratory of Urban and Regional Ecology Research Center for Eco-Environmental SciencesChinese Academy of Sciences Shuangqing Road 18 Haidian District Beijing 100085 China3Jiangsu Provincial Key Laboratory of Geographic Information Science and Technology International Institute for EarthSystem Science Nanjing University Nanjing 210023 China4State Key Laboratory of Environmental Criteria and Risk Assessment Chinese Research Academy of EnvironmentalSciences Beijing 100012 China5Laboratory for Climate and Ocean-Atmosphere Sciences Department of Atmospheric and Oceanic SciencesSchool of Physics Peking University Beijing 100871 China6State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC)Institute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029 China7School of Agriculture and Food Sciences The University of Melbourne Victoria 3010 Australia8Department of Land Management Zhejiang University Hangzhou 310058 China9Arizona Department of Environmental Quality Phoenix AZ 85007 USA10Institute of Subtropical Agriculture Chinese Academy of Sciences Changsha 410125 China11Institute of Surface-Earth System Science Tianjin University Tianjin 300072 China12Institute of Plant Nutrition Resources and Environmental Sciences Henan Academy of Agricultural SciencesHenan Key Laboratory of Agricultural Eco-environment Zhengzhou 450002 China13State Key Laboratory of Pollution Control amp Resource Reuse School of the Environment Nanjing University163 Xianlin Ave Nanjing Jiangsu 210023 China14Department of Atmospheric Science Colorado State University Fort Collins Colorado 80523 USA

Correspondence Xuejun Liu (liu310caueducn) and Zhaozhong Feng (fzzrceesaccn)

Received 26 April 2018 ndash Discussion started 15 May 2018Revised 11 July 2018 ndash Accepted 17 July 2018 ndash Published 6 August 2018

Abstract Five-year (2011ndash2015) measurements of gaseousNH3 NO2 and HNO3 and particulate NH+4 and NOminus3 in airandor precipitation were conducted at 27 sites in the Nation-wide Nitrogen Deposition Monitoring Network (NNDMN)to better understand spatial and temporal (seasonal and an-nual) characteristics of reactive nitrogen (Nr) concentrationsand deposition in eastern China Our observations reveal an-nual average concentrations (164ndash326 microg N mminus3) dry depo-sition fluxes (158ndash317 kg N haminus1 yrminus1) and wetbulk depo-sition fluxes (184ndash280 kg N haminus1 yrminus1) based on land use

ranked as urban gt rural gt background sites Annual concen-trations and dry deposition fluxes of each Nr species in airwere comparable at urban and background sites in northernand southern regions but were significantly higher at north-ern rural sites These results together with good agreementbetween spatial distributions of NH3 and NO2 concentrationsdetermined from ground measurements and satellite obser-vations demonstrate that atmospheric Nr pollution is heavierin the northern region than in the southern region No sig-nificant inter-annual trends were found in the annual Nr dry

Published by Copernicus Publications on behalf of the European Geosciences Union

10932 W Xu et al Spatialndashtemporal patterns of inorganic nitrogen air concentrations

and wetbulk N deposition at almost all of the selected sitesA lack of significant changes in annual averages between the2013ndash2015 and 2011ndash2012 periods for all land use types sug-gests that any effects of current emission controls are not yetapparent in Nr pollution and deposition in the region Ambi-ent concentrations of total Nr exhibited non-significant sea-sonal variation at all land use types although significant sea-sonal variations were found for individual Nr species (egNH3 NO2 and pNOminus3 ) in most cases In contrast dry depo-sition of total Nr exhibited a consistent and significant sea-sonal variation at all land use types with the highest fluxes insummer and the lowest in winter Based on sensitivity testsby the GEOS-Chem model we found that NH3 emissionsfrom fertilizer use (including chemical and organic fertiliz-ers) were the largest contributor (36 ) to total inorganic Nrdeposition over eastern China Our results not only improvethe understanding of spatialndashtemporal variations of Nr con-centrations and deposition in this pollution hotspot but alsoprovide useful information for policy-makers that mitigationof NH3 emissions should be a priority to tackle serious Ndeposition in eastern China

1 Introduction

In China and globally human activities have dramaticallyincreased emissions of nitrogen oxides (NOx =NO+NO2)and ammonia (NH3) into the atmosphere since the beginningof the industrial revolution (Galloway et al 2008 Liu et al2013) NOx and NH3 emitted into the atmosphere are trans-formed to nitrogen-containing particles (eg particulate NH+4and NOminus3 and organic nitrogen Ianniello et al 2010 Zhanget al 2015) which are major chemical constituents of air-borne PM25 (particulate matter with a diameter of 25 microm orless) and have implications for air quality and climate (Fuzziet al 2015) As a result of elevated reactive nitrogen (Nr)emissions nitrogen (N) deposition through dry and wet pro-cesses has also substantially increased over China (Liu et al2013 Lu et al 2007 2014 Jia et al 2014 2016) and exces-sive deposition of N has resulted in detrimental impacts in-cluding decreased biological diversity (Bobbink et al 2010)nutrient imbalance (Li et al 2016) increased soil acidifica-tion (Yang et al 2015) and eutrophication of water bodies(Fenn et al 2003) Furthermore Nr-associated haze pollu-tion episodes characterized by high concentrations of PM25occur frequently in China as evidenced in particular in 2013(Guo et al 2014 Huang et al 2014 Tian et al 2014)

In order to control its notorious air pollution China hasreduced national emissions of SO2 and particulate matterby 14 and 30 respectively from 2005 to 2010 (MEPC2011) Additionally stringent measures (eg using selectivecatalyticnon-catalytic reduction systems and implementingtighter vehicle emission standards) were implemented dur-ing the 12th Five Year Plan (FYP) period (2011ndash2015) with

aims to reduce 2015 annual emissions of SO2 and NOx by8 and 10 respectively relative to 2010 levels (Xia et al2016) However there is as yet no regulation or legislationthat deals with national NH3 emissions and thus the emis-sion reductions of SO2 and NOx used to achieve desiredair-quality improvement goals will be compromised (Gu etal 2014) Significant increases in PM25 concentrations havebeen observed in the years 2013 and 2014 as compared to2012 excluding the influence of meteorological conditionson inter-annual variations (Liang et al 2015) Other stud-ies with more conclusive evidence have likewise suggestedthat NH3 plays a vital role in sulfate formation and exacer-bates severe haze pollution development in urban regions ofChina (Wang et al 2016) even acting as the key limitingfactor for the formation of secondary inorganic aerosol (Wuet al 2016) In addition due to higher local and regionalconcentrations of NH3 in the atmosphere nitrate-driven hazepollution occurred during summertime in urban environmentin the North China Plain (Li et al 2018) The absolute andrelative concentrations of particulate nitrate in urban Beijingincreased with haze development (Pan et al 2016) Alsonitrate contributed to a large fraction of the elevated PM25concentrations at a rural site in the North China Plain andhigh NH3 in the early morning accelerated the formation offine nitrates (Wen et al 2015)

High rates of N deposition have also been observed dur-ing 2011ndash2014 across China (Xu et al 2015) However todate no study based on long-term ground-based observa-tions has provided any information on the effectiveness ofSO2 and NOx emission controls on N deposition in ChinaNon-linearities have been identified between reductions inemissions and deposition in Europe over the last 3 decades(Aguillaume et al 2016 Fowler et al 2007) Due to thetightly coupled yet complex relationship between emissionsconcentrations and deposition long-term monitoring net-works can test the effectiveness of emission controls (Eris-man et al 2003) Currently two national N deposition net-works are operational in China ie the Nationwide NitrogenDeposition Monitoring Network (NNDMN Liu et al 2011Xu et al 2015) and the Chinese Ecosystem Research Net-work (CERS Zhu et al 2015) The NNDMN containing43 in situ monitoring sites has been measuring wet N depo-sition and ambient concentrations of five major Nr species(ie gaseous NH3 NO2 and HNO3 and particulate NH+4and NOminus3 ) since 2010 the latter species for subsequent esti-mation of dry deposition The CERS was established in 1988and has been mainly focused on wet N deposition at 41 fieldstations In addition to ground-based measurements satelliteobservations enable retrieval of atmospheric NH3 and NO2with high temporal and spatial resolutions (Dammer et al2016 Russell et al 2012) providing a means to reveal spa-tial distributions and long-term trends of ambient NH3 andNO2 levels at regional to global scales and also to evaluatethe effectiveness of emission controls (Krotkov et al 2016)However to effectively use the vast satellite data sets for en-

Atmos Chem Phys 18 10931ndash10954 2018 wwwatmos-chem-physnet18109312018

W Xu et al Spatialndashtemporal patterns of inorganic nitrogen air concentrations 10933

vironmental monitoring it is critical to validate these remotesensing observations using in situ surface observations (Pin-der et al 2011 Van Damme et al 2015)

Eastern China is a developed region with the largest densi-ties of population economic activity and resource consump-tion in the country (He et al 2015) Recent satellite observa-tions indicate that tropospheric NH3 and NO2 levels in east-ern China were both much greater than other regions of theworld over 2005ndash2015 (Demmer et al 2016 Krotkov et al2016) Accordingly this region received the highest levelsof dry N deposition in the world (Vet et al 2014) and wasregarded as a primary export region of N deposition to neigh-bouring countries (Ge et al 2014) Based on meta-analysisof published observations some studies have provided infor-mation on the magnitudes spatial distributions and decadalvariations of wetbulk N deposition in China (Liu et al 2013Jia et al 2014) but the analysed data were limited to timeperiods between 1980 and 2010 Although a recent study (Jiaet al 2016) has reported a clear increasing trend of dry Ndeposition in eastern China between 2005 and 2014 con-siderable uncertainty may exist due to estimates of gaseousHNO3 and particulate NH+4 and NOminus3 (pNH+4 and pNOminus3 )concentrations using NO2 satellite data which is in part man-ifested in Liu et al (2017a) Furthermore seasonal patternsof Nr concentrations and deposition have not yet been sys-tematically investigated at a large spatial scale in this regionalthough spatial patterns of dry Nr deposition for represen-tative months of four seasons (ie January for winter Aprilfor spring July for summer October for autumn) in 2010have been mapped with the RAMS-CMAQ model (Han et al2017) Thus the spatial and temporal (annual and seasonal)variations of Nr concentrations and dry and wet depositionin eastern China require further exploration using ground-based measurements especially for time periods after 2010Our previous work (Xu et al 2015) used multi-year mea-surements (mainly from January 2010 to September 2014) atthe 43 sites in the NNDMN aiming to provide the first quan-titative information on atmospheric Nr concentrations andpollution status across China and to analyse overall fluxesand spatial variations of Nr deposition in relation to anthro-pogenic Nr emissions from six regions

The present study aims to examine spatialndashtemporal (an-nual and seasonal) characteristics of Nr concentrations inair (NH3 NO2 HNO3 pNH+4 and pNOminus3 ) and precipi-tation (NH+4 -N and NOminus3 -N) and their corresponding dryand wetbulk N deposition through a 5-year (2011ndash2015)monitoring period at 27 NNDMN sites in eastern China Inaddition we compare spatialndashtemporal variability of mea-sured NH3 and NO2 concentrations with variations of thecorresponding satellite retrieval columns as well as inter-annual trends in Nr deposition and emissions Finally emis-sion sources contributing to total N deposition over easternChina are examined

2 Materials and methods

21 Study area and site descriptions

The present study was conducted in eastern China whichis distinguished by the ldquoHu Linerdquo (She 1998) This regionhas spatial heterogeneity in levels of economic developmentand significant spatial differences in NH3 and NOx emissions(Fig 1b and c) Thus to better analyse spatial and temporalvariabilities in measured Nr concentrations and depositionwe divided eastern China into northern and southern regionsusing the Qinling MountainsndashHuaihe River line (Fig 1a)the division basin of which was based on the differences innatural conditions agricultural production geographical fea-tures and lifestyle As for specific differentiations for exam-ple the northern region adopted a centralized domestic heat-ing policy for late autumn and winter seasons but the southhas not annual average precipitation amounts were generallygreater than 800 mm in the south but were less than 800 mmin the north In addition the north is dominated by calcare-ous soils which could result in higher soil NH3 volatilization(Huang et al 2015) vs the acidic red soil in the south

The NNDMN was operated in line with international stan-dards by China Agricultural University (CAU) 35 NNDMNsites were located in eastern China (Xu et al 2015) For ouranalysis we considered 27 sites in total with 5-year con-tinuous data 13 sites were located in north of the QinlingMountainsndashHuaihe River line (China Agricultural Univer-sity CAU Zhengzhou ZZ Dalian DL Shangzhuang SZQuzhou QZ Yangqu YQ Zhumadian ZMD Yanglin YLYucheng YC Gongzhuling GZL Lishu LS LingshandaoLSD Changdao CD) and 14 sites were located in south ofthe line (Nanjing NJ Baiyun BY Wenjiang WJ WuxueWX Taojing TJ Fengyang FYA Zhanjiang ZJ FuzhouFZ Fenghua FH Ziyang ZY Yangting YT Jiangjin JJHuinong HN Xishan XS)

All the sites are located as far away as possible and prac-tical from local direct emission sources to increase regionalrepresentativeness They can be divided into three categoriesaccording to their geopolitical location and their proximityto the main emission sources urban sites (abbreviated as U)rural sites (cropland areas R) and background sites (coastaland forest areas B) Information on the monitoring sitessuch as land use types coordinates and measurement periodsare listed in Table S1 of the Supplement Detailed descrip-tions of all the sites including the surrounding environmentand nearby emission sources can be found in Xu et al (2015)

22 Field sampling and chemical analysis

Continuous measurements were performed during the periodfrom January 2011 to December 2015 at the 27 study sitesexcept for 11 sites (ZZ ZMD YC LSD NJ WX FYA ZJYT JJ and HN) where field sampling was carried out af-ter the year 2011 (ie the years between 2012 and 2015)

wwwatmos-chem-physnet18109312018 Atmos Chem Phys 18 10931ndash10954 2018

Figure 1 Spatial distributions of the 27 monitoring sites (a) NOx emissions (b) and NH3 emissions (c) in eastern China (NH3 and NOx

emission data were for the year 2010 and obtained from Liu et al 2017b) The blue and red lines refer to the QinlingndashHuaihe line and Huline respectively

andor interrupted during the period due to instrument fail-ure (details in Table S1 Supplement) Ambient Nr concen-trations of gaseous NH3 and HNO3 andpNH+4 and pNOminus3(for which the empirically determined effective size cut-offfor aerosol sampling is of the order of 45 microm) were mea-sured using an active DELTA (DEnuder for Long-Term At-mospheric sampling Tang et al 2009) system gaseous NO2was sampled in three replicates with passive diffusion tubes(Gradko International Limited UK) The air intakes of theDELTA system and the NO2 tubes were mounted 2 m abovethe ground at most sites and protected from precipitationand direct sunlight with a rigid plastic box and a PVC shel-ter respectively All measurements of Nr concentration werebased on monthly sampling (one sample per month for eachNr species) Detailed information on measuring methods andcollection are given in Sect S1 of the Supplement

To collect precipitation (here termed as wetbulk deposi-tion which contains wet and some dry deposition due to theuse of an open sampler) samples a standard precipitationgauge (SDM6 Tianjin Weather Equipment Inc China) wascontinuously exposed beside the DELTA system (sim 2 m) Im-mediately after each precipitation event (0800ndash0800 the fol-lowing day Greenwich Mean Time +8) samples (includingrain and melted snow) were collected and stored in cleanpolyethylene bottles (50 mL) atminus18 C until sent to the CAU

laboratory for analysis Each collector was rinsed three timeswith high-purity water after each collection

In the analytical laboratory acid-coated denuders andaerosol filters were extracted with 6 and 10 mL of high-puritywater (182 M) respectively and analysed for NH+4 -N withan AA3 continuous-flow analyser (CFA BranC LuebbeGmbH Norderstedt Germany) Carbonate-coated denudersand filters were both extracted with 10 mL 005 H2O2 so-lution followed by analysis of NO3-N using the same CFANO2 samples extracted with a solution containing sulfanil-amide H3PO4 and N-1-naphthylethylene-diamine were de-termined using a colorimetric method by absorption at awavelength of 542 nm (Xu et al 2016) Precipitation sam-ples were filtered through a syringe filter (045 mm TengdaInc Tianjin China) and analysed for NH+4 -N and NOminus3 -Nusing the CFA as mentioned above Quality assurance andquality control procedures adopted in the analytical labora-tory are described by Xu et al (2017) Further details ofprecipitation measurement samples handling and chemicalanalysis are reported in Xu et al (2015)

23 Deposition estimate

Wetbulk deposition of NH+4 -N and NOminus3 -N were calculatedper month and year by multiplying the precipitation amount

by their respective volume-weighted mean (VWM) concen-trations The dry deposition flux of gaseous and particulateNr species was calculated as the product of measured con-centrations by modelled deposition velocities (Vd) The drydeposition velocities of five Nr species were calculated by theGEOS (Goddard Earth Observing System)-Chem chemicaltransport model (CTM Bey et al 2001 httpgeos-chemorg) and have been reported in a companion paper (Xu etal 2015) In brief the model calculation of dry depositionof Nr species follows a standard big-leaf resistance-in-seriesmodel as described by Wesely (1989) for gases and Zhanget al (2001) for aerosol We used archived hourly Vd fromJanuary 2011 to May 2013 and filled the gap for the period(from June 2013 to December 2015) when GEOS meteoro-logical data are unavailable using the mean values calculatedfrom all the available simulations The monthly Vd at eachsite was averaged from the hourly data set

24 Satellite retrievals of NH3 and NO2

Comparisons between satellite observations and ground-based measurements were evaluated at the 27 sites in orderto accurately examine the spatialndashtemporal pattern of NH3and NO2 concentrations For NH3 we used the productsretrieved from the Infrared Atmospheric Sounding Interfer-ometer (IASI) instrument (aboard the MetOp-A platform)which crosses the equator at a mean local solar time of 0930and 2130 The IASI-NH3 product is based on the calculationof a spectral hyperspectral range index and subsequent con-version to NH3 total columns via a neural network The de-tails of the IASI-NH3 retrieval method are described in Whit-burn et al (2016) We only considered the observations fromthe morning overpass as they are generally more sensitive toNH3 because of higher thermal contrast at this time of day(Van Damme et al 2015 Dammers et al 2016) The dailyIASI-NH3 data (provided by the Atmospheric SpectroscopyGroup at Universiteacute Libre De Bruxelles data available athttpiasiaeris-datafrNH3) from 1 January 2011 to 31 De-cember 2015 was used for the spatial analysis in the presentstudy For the temporal analysis we used the IASI_NH3from 1 January 2011 to 30 September 2014 because anupdate of the input meteorological data on 30 September2014 had caused a substantial increase in the retrieved atmo-spheric NH3 columns Only observations with a cloud cover-age lower than 25 and relative error lower than 100 orabsolute error smaller than 5times 1015 molecules cmminus2 wereprocessed The methodology is provided in detail in Liu etal (2017b) In brief all observations were gridded to a 05

latitudetimes 05 longitude grid and then we calculated themonthly arithmetic mean by averaging the daily values withobservations points within each grid cell Similarly we cal-culated the annual arithmetic mean by averaging the dailyvalues with observations points within the grid cell over thewhole year

For NO2 we used the products from the Ozone Monitor-ing Instrument (OMI) onboard NASArsquos EOS-Aura satellitewhich was launched in July 2004 into a sun-synchronousorbit with a local equator crossing time at approximately1345 OMI detects the backscattered solar radiation from theEarthrsquos atmosphere within the UVndashVis spectral window be-tween 270 and 500 nm to achieve nearly global coveragedaily with a spatial resolution ranging from 13 kmtimes 24 kmat nadir to 24 kmtimes 128 km at the edge of the swath (Russellet al 2012) We used tropospheric NO2 retrievals from theDOMINO (DutchndashFinnish Ozone Monitoring Instrument)algorithm version 2 The retrieval algorithm is describedin detail in Boersma et al (2007) The tropospheric NO2columns used in this study are monthly means from 1 Jan-uary 2011 to 30 December 2015 with a spatial resolutionof 0125 latitudetimes 0125 longitude (data available at httpwwwtemisnlairpollutionno2html)

25 Statistical analysis

One-way analysis of variance (ANOVA) and two indepen-dent samples t tests were applied to detect significant differ-ences in seasonal mean concentrations and deposition fluxesof measured Nr species as well as their annual mean deposi-tion fluxes for three land use types (rural urban and back-ground) As there was large site-to-site variability in annualNr concentrations and deposition fluxes at monitoring siteswithin the same land use types averaging data into annualvalues for land use types is unlikely to be truly representativeof actual trends Thus annual trends of the variables wereevaluated at a single site scale rather than by land use typeTrend analysis was conducted using Theil regression (Theil1992) and the MannndashKendall test (Gilbert 1987 Marchettoet al 2013) We defined an increasing (decreasing) trend as apositive (negative) slope of the Theil regression while a sta-tistical significance level (p lt 001) of a trend was evaluatedby the non-parametric MannndashKendall test (p value) Non-parametric methods usually have the advantage of being in-sensitive to outliers and allow missing data and non-normaldistribution of data (Gilbert 1987 Salmi et al 2002) appro-priate for the analysed data set The MannndashKendall methodis appropriate for detection of monotonic trends in data se-ries that have no seasonal variation or autocorrelation Atmo-spheric concentrations and deposition fluxes of Nr specieshowever generally have distinct seasonal variability (Pan etal 2012) and the MannndashKendall test is thus applied to an-nual values

Satellite observations during 2005ndash2015 indicate that tro-pospheric NO2 levels peaked in 2011 over China (Krotkov etal 2016 Duncan et al 2016) and NOx emissions peakedin 20112012 (Miyazaki et al 2017 van der A et al2017 Souri et al 2017) To assess the impact of emis-sion control measures on measured Nr concentrations anddeposition fluxes at different land use types we comparedarithmetic mean values averaged from the last 3-year pe-

riod (2013ndash2015) with those averaged from the first 2-yearperiod (2011ndash2012) for monitoring sites with continuous5-year measurements (21 sites for dry and 17 sites forwetbulk) Seasonal concentrations and deposition fluxes ofmeasured Nr species were calculated using the arithmeticaverage of matched seasons during the sampling periodsspring refers to MarchndashMay summer covers JunendashAugustautumn refers to SeptemberndashNovember and winter coversDecemberndashFebruary

3 Results

31 Spatial variability in concentrations of Nr speciesin air and precipitation

Summary statistics of monthly mean concentrations of NH3NO2 HNO3 pNH+4 and pNOminus3 at the 27 monitoring sitesduring 2011ndash2015 are listed in Table S2 of the Supple-ment Monthly mean concentrations of NH3 NO2 HNO3pNH+4 and pNOminus3 ranged over 016ndash3957 (TJ and WJ)055ndash2906 (LS and WJ) 004ndash493 (YQ and CAU) 011ndash5720 (ZY and QZ) and 001ndash3206 microg N mminus3 (DL and ZZ)respectively On the basis of geographical location and classi-fication of each site the annual mean concentrations of eachNr species were calculated for three land use types in easternChina and its northern and southern regions (Table 1)

In eastern China annual mean concentrations of NH3NO2 HNO3 pNH+4 and pNOminus3 at the urban sites (aver-ages for the 5-year 16plusmn 02 (for HNO3) to 102plusmn 10 (forNO2) microg N mminus3) increased by 18 70 33 23 and 43 re-spectively compared with their corresponding concentrationsat the rural sites (12plusmn 10 (for HNO3) to 72plusmn 09 (forNH3) microg N mminus3) they also increased by 78ndash118 comparedwith the concentrations at the background sites (09plusmn 01(for HNO3) to 52plusmn 03 (for NO2) microg N mminus3 Table 1) Anal-ogous patterns also occurred for all measured Nr in each re-gion except for NH3 and pNH+4 in the northern region forwhich the mean concentrations were 18 and 7 lower at theurban sites than at the rural sites respectively

Comparing northern vs southern regions (Table 1)at urban sites the annual mean concentrations of NH3HNO3 and pNH+4 showed smaller non-significant differ-ences (minus1sim 9 ) whereas NO2 and pNOminus3 showed largernon-significant increases (34 and 76 respectively) in thenorth By contrast the mean concentrations of all mea-sured Nr species were significantly (p lt 005) higher (by 40ndash104 ) at rural sites in northern region Similarly individ-ual concentrations at background sites were 21ndash71 higherin the northern than southern region Averaged across threeland use types the annual mean Nr concentrations of five Nrspecies in the north increased to varying extents (by 84 for pNOminus3 63 for pNH+4 57 for NH3 47 for NO2and 28 for HNO3) compared with those in the south Theannual concentrations of total Nr (ie the sum of five Nr

species) decreased in the order urban gt rural gt backgroundin eastern China as a whole and in the north and south re-gions further the annual total Nr concentrations at urbanand background sites were 17 and 34 higher (p gt 005)in the north than in the south respectively whereas thoseat northern rural sites (316plusmn 38 microg N mminus3) were signifi-cantly (p lt 005) higher than the means at southern rural sites(170plusmn 17 microg N mminus3)

The monthly VWM concentrations of NH+4 -N NOminus3 -Nand TIN (the sum of NH+4 -N and NOminus3 -N) were in the ranges001ndash2677 (BY and YC) 006ndash2892 (XS and WJ) and009ndash5029 mg N Lminus1 (XS and YC) respectively (Table S3Supplement) In eastern China and in each region the an-nual VWM concentrations of NOminus3 -N and TIN showed a de-clining trend of urban gt rural gt background whereas those ofNH+4 -N followed the order ruralge urban gt background (Ta-ble 1) Comparing northern and southern regions the annualconcentrations of NH+4 -N NOminus3 -N and TIN were compa-rable at urban and background sites and were significantly(p lt 005) higher at northern rural sites

32 Annual variability in concentrations of Nr speciesin air and precipitation

During the 2011ndash2015 period the annual mean concentra-tions of measured Nr species in air exhibited no significanttrends at the 21 selected sites except for NH3 at 4 sites (ZZDL ZMD YL) HNO3 at 3 sites (DL LSD BY) pNH+4 at1 site (XS) and total Nr at 3 sites (ZMD YL WJ Fig S1andashf Supplement) Similarly no significant trends were foundfor the annual VWM concentrations of NH+4 -N NOminus3 -N andTIN in precipitation at the 17 selected sites with the excep-tion of NOminus3 -N at 1 site (SZ Fig S2andashc Supplement)

Figure 2 compares annual average concentrations of allmeasured Nr species between the periods 2013ndash2015 and2011ndash2012 for three land use types In eastern Chinathe mean concentrations of NH3 and pNH+4 showed non-significant increases (10ndash38 ) at all land use types exceptpNH+4 at background sites which showed a small reduction(8 Fig 2a d) By contrast the mean concentrations of re-maining Nr species at three land use types showed smallerand non-significant changes minus8sim 3 for NO2 (Fig 2b)minus13sim 5 for HNO3 (Fig 2c) and minus1sim 5 for pNOminus3(Fig 2e) The relative changes in the annual total Nr con-centration were also not significant with the largest increaseat rural sites (16 ) and smaller increases at urban (4 ) andbackground (1 ) sites (Fig 2f) Separated by regions an-nual mean concentrations of five Nr species at three land usetypes mostly showed increases (4ndash57 ) in the north andreductions (03ndash21 ) in the south (Fig 2andashf) The relativechanges in individual concentrations at northern rural sites(9 reduction for HNO3 and 9ndash52 increases for the otherspecies) and southern rural sites (4 increase for pNH+4 and 03ndash21 reductions for other species) were not signifi-cant The annual total Nr concentrations showed small rela-

Table 1 Annual average (standard error) concentrations of various Nr compounds in air and precipitation at different land use types ineastern China and its northern and southern regions for the 5-year period 2011ndash2015

Regiona LUTb Ambient conc microg N mminus3 Rainwater conc mg N Lminus1

NH3 NO2 HNO3 pNH+4 pNOminus3 Total Nr NH+4 NOminus3 TIN

EC urban 85 102 16 82 40 326 16 19 35(n= 6) (14) (10) (02) (18) (08) (41) (03) (02) (05)rural 72 60 12 67 28 239 17 14 31(n= 17) (09) (05) (01) (11) (03) (27) (02) (02) (04)BKDc 39 52 09 45 19 164 14 12 26(n= 4) (06) (03) (01) (04) (03) (14) (03) (04) (06)

NREC urban 81 117 16 86 51 351 22 24 46(n= 3) (24) (16) (03) (23) (14) (77) (04) (02) (04)rural 99 74 14 92 37 316 24 20 44(n= 8) (12)lowastlowast (07)lowast (01)lowast (19)lowast (05)lowast (38)lowastlowast (03)lowastlowast (02)lowastlowast (04)lowastlowast

BKD 47 57 10 51 24 188 18 15 33(n= 2) (06) (03) (01) (02) (03) (01) (02) (03) (01)

SREC urban 89 87 16 79 29 301 11 15 26(n= 3) (18) (06) (01) (31) (02) (45) (03) (03) (06)rural 49 46 10 45 19 170 11 09 20(n= 9) (06) (06) (01) (06) (02) (17) (02) (01) (03)BKD 31 47 08 40 14 140 10 06 16(n= 2) (07) (04) (01) (02) (02) (06) (00) (00) (00)

a EC eastern China NREC northern region of eastern China SREC southern region of eastern China b LUT land use type n denotes number ofmonitoring sites c BKD Background ldquoconcrdquo concentration lowast and lowastlowast denote significance at the 005 and 001 probability levels for difference in annualmean Nr concentrations at a given site type between northern and southern regions respectively

tive changes (fromminus1 to 5 ) across all land use types in thetwo regions except at northern rural sites which exhibited alarger but non-significant increase (25 Fig 2f) Due to sig-nificant interannual variability longer records are needed tobetter assess the significance of any concentration changes

In eastern China the annual VWM concentrations ofNH+4 -N NOminus3 -N and TIN showed the largest increase of26ndash31 at background sites a smaller increase of 4ndash5 atrural sites and a decrease of 2ndash14 at urban sites howeverthose changes were not significant (Fig 2gndashi) Regionallytheir respective concentrations showed increases (3ndash45 ) inthe north and reductions (5ndash33 ) in the south except for asmall increase (4 ) in NH+4 -N at background sites

33 Seasonal variability in concentrations of Nr speciesin air and precipitation

Figure 3 shows seasonal patterns of NH3 NO2 HNO3pNH+4 pNOminus3 and total Nr concentrations for three landuse types in eastern China and its northern and south-ern regions averaged from corresponding measurements atthe 27 study sites (details for each site are given in Ta-bles S4ndashS9 of the Supplement) Average NH3 concentra-tions at all land use types decreased in the order sum-mer gt spring gt autumn gt winter and significant seasonal dif-ferences generally occurred between summer and winter(Fig 3a) Conversely the average NO2 concentration gen-

erally showed the highest value in winter and the lowest insummer differences between seasonal concentrations weresometimes significant at rural sites in the south and back-ground sites but not at urban sites (Fig 3b) The seasonalchanges in the HNO3 concentration were generally small andnot significant for all land use types (Fig 3c)

The average pNH+4 concentration exhibited a non-significant seasonal variation across all land use types exceptfor southern rural sites which showed significantly highervalues in winter than in summer (Fig 3d) The highestpNH+4 concentrations mostly occurred in winter The av-erage pNOminus3 concentrations at all land use types followedthe order winter gt springasymp autumn gt summer the seasonalchanges are sometimes significant except for urban sitesin eastern China and its northern region (Fig 3e) The av-erage concentration of total Nr usually showed small andnon-significant seasonal differences for all land use types(Fig 3f)

In eastern China and its two regions the seasonal VWMconcentrations of NH+4 -N NOminus3 -N and TIN in precipitationat three land use types (averaged from the 27 sites detailsin Tables S10ndashS12 of the Supplement) showed a similar sea-sonal pattern with the highest values in winter and the lowestin summer or autumn (Fig 4andashc) Significant seasonal dif-ferences usually occurred between winter and the other three

Figure 2 Comparison of annual mean concentrations of (a) NH3 (b) NO2 (c) HNO3 (d) pNH+4 and (e) pNOminus3 (f) total Nr ie the sumof all measured Nr in air volume-weighted concentrations of NH+4 (g) NOminus3 (h) total inorganic N (TIN) sum of NH+4 and NOminus3 (i) inprecipitation between the 2011ndash2012 period and the 2013ndash2015 period for different land use types in eastern China and its northern andsouthern regions U R and B denote urban rural and background sites respectively The number of sites for each land use type in eachregion can be found in Table S1 in the Supplement The error bars are the standard errors of means

seasons at all land use types except background sites andsouthern urban sites

34 Spatial variability in dry and wetbulk N depositionof Nr species

Dry deposition fluxes of NH3 HNO3 NO2 pNH+4 andpNOminus3 ranked in the order urban gt rural gt background ineastern China and in both southern and northern regions (ex-cept for pNH+4 in the north Table 2) Comparing northernand southern regions at urban sites the mean dry pNH+4 de-position was slightly higher (2 ) in the north whereas largerenhancements (24ndash69 ) in the mean fluxes were found inthe north for the remaining Nr species By contrast individ-ual fluxes were significantly higher (by 64ndash138 ) at north-ern rural sites except for HNO3 which showed a large non-significant increase (58 ) At northern background sites themean dry deposition fluxes of NH3 and NO2 were muchhigher (159 ) and lower (68 ) respectively however onlysmall differences in the means were found for HNO3 (6 lower in the north) pNH+4 (5 lower) and pNOminus3 (14

higher) The spatial pattern of total N dry deposition flux (thesum of the fluxes of the five Nr species) by land use typesranked in the same order as individual Nr species in east-ern China Compared with the southern region mean total Nfluxes in the north region were significantly higher (by 85 )at rural sites but showed non-significant increases at urbanand background sites (33 and 38 respectively)

The wetbulk deposition fluxes of NH+4 -N NOminus3 -N andTIN ranked in the order urban gt rural gt background in easternChina and in each region (except for NH+4 -N in the southTable 2) In addition their respective fluxes were generallycomparable in northern and southern regions

35 Annual variability in dry and wetbulk Ndeposition

The annual trends of dry deposition fluxes of individual Nrspecies at the 21 selected sites are consistent with trends intheir respective ambient concentrations except for HNO3at three sites (SZ LSD and ZY Figs S3andashe and S1andasheSupplement) A consistent picture is also seen for the total

Figure 3 Seasonal mean concentrations averaged over 2011ndash2015 of (a) NH3 (b) NO2 (c) HNO3 (d) pNH+4 (e) pNOminus3 and (f) total Nrie the sum of all measured Nr in air at different land use types in eastern China and its northern and southern regions Sp Su Au and Wirepresent spring summer autumn and winter respectively U R and B denote urban rural and background sites respectively The numberof sites for each land use type in each region can be found in Table 1 The error bars are the standard errors of means and values withoutsame letters on the bars denote significant differences between the seasons (p lt 005)

dry N deposition fluxes at all but two sites (DL and WJFigs S3f and S1f Supplement) Similarly the annual trendsof wetbulk deposition fluxes of NH+4 -N NOminus3 -N and TIN at17 selected sites are similar to their respective concentrationsin precipitation (Fig S4andashc Supplement)

In eastern China the annual average dry deposition fluxesof NH3 NO2 HNO3 pNH+4 and pNOminus3 showed non-significant increases (2ndash39 ) or reductions (1ndash19 ) be-tween the periods 2011ndash2012 and 2013ndash2015 at the threeland use types (Fig 5andashe) similar in sign and magnitude totheir respective concentrations described earlier The annualaverage total N dry deposition fluxes showed small and non-significant increases across the study periods 2 at urbansites 9 at rural sites and 7 at background sites (Fig 5f)The sign and magnitude of period-to-period changes in dry

deposition and ambient concentrations of all measured Nrspecies were generally similar between the southern andnorthern regions

Wetbulk deposition fluxes of NH+4 -N NOminus3 -N andTIN generally decreased (4ndash29 ) between 2011ndash2012 and2013ndash2015 at all land use types in eastern China one excep-tion was NOminus3 -N which exhibited a small increase (3 ) aturban sites (Fig 5g-i) Similar tendencies were also observedin both northern and southern regions

36 Seasonal variability in dry and wetbulk depositionof Nr species

Seasonal variations of dry deposition of individual Nr speciesat each site are shown in Tables S4ndashS9 in the Supple-

Figure 4 Seasonal mean concentrations averaged over 2011ndash2015 of NH+4 (a) NOminus3 (b) and total inorganic N (TIN) ie the sum of NH+4and NOminus3 (c) in precipitation at different land use types in eastern China and its northern and southern regions Sp Su Au and Wi representspring summer autumn and winter respectively U R and B denote urban rural and background sites respectively The number of sites foreach land use type in each region can be found in Table 1 The error bars are the standard errors of means and values without same letterson the bars denote significant differences between the seasons (p lt 005)

Table 2 Annual average (standard error) dry and wetbulk deposition fluxes (kg N haminus1 yrminus1) of various Nr compounds at different land usetypes in eastern China and its northern and southern regions for the 5-year period 2011ndash2015

Regiona LUTb Dry deposition Wetbulk deposition

EC Urban 126 44 77 48 21 317 126 154 280(n= 6) (14) (12) (16) (14) (05) (46) (19) (07) (22)Rural 91 29 46 40 15 221 119 102 221(n= 17) (09) (03) (06) (07) (02) (23) (10) (05) (14)BKDc 79 18 35 19 08 158 107 77 184(n= 4) (21) (06) (02) (03) (01) (15) (18) (03) (18)

NREC Urban 139 52 94 49 27 362 139 141 280(n= 3) (19) (25) (30) (19) (10) (82) (35) (10) (44)Rural 121lowastlowast 36lowast 57 57lowast 21lowastlowast 293lowastlowast 123 103 226(n= 8) (13) (04) (10) (12) (03) (32) (13) (07) (18)BKD 114 09 34 19 08 184 78 76 154(n= 2) (06) (07) (03) (07) (02) (07) (14) (08) (06)

SREC Urban 112 36 59 48 16 272 114 166 280(n= 3) (20) (03) (06) (26) (02) (40) (20) (04) (21)Rural 65 22 36 24 10 158 116 102 218(n= 9) (05) (04) (06) (04) (02) (14) (15) (09) (22)BKD 44 27 36 20 07 133 136 79 215(n= 2) (10) (02) (03) (01) (01) (07) (01) (01) (01)

a EC eastern China NREC northern region of eastern China SREC southern region of eastern China b LUT land use type n denotes numberof monitoring sites c BKD Background lowast and lowastlowast denote significance at the 005 and 001 probability levels for difference in annual mean Nrconcentrations at a given site type between northern and southern regions respectively

Figure 5 Comparison of dry deposition of (a) NH3 (b) NO2 (c) HNO3 (d) pNH+4 (e) pNOminus3 and (f) total Nr sum of all measured Nr

in air and wetbulk deposition of NH+4 (g) NOminus3 (h) and total inorganic N (TIN) sum of NH+4 and NOminus3 (i) in precipitation between the2011ndash2012 period and the 2013ndash2015 period for different land use types in eastern China and its northern and southern regions U R and Bdenote urban rural and background sites respectively The number of sites for each land use type in each region can be found in Table S1 inthe Supplement The error bars are the standard errors of means

ment In eastern China and in each region dry NH3 depo-sition fluxes at all land use types followed the order sum-mer gt spring gt autumn gt winter with the seasonal changesusually significantly different (Fig 6a) Similarly the dryNO2 deposition flux was also at its minimum in winter but itsmaximum was found in summer at urban and rural sites andin autumn at background site seasonal differences in mostcases were not significant (Fig 6b) Seasonal patterns of dryHNO3 deposition flux at all land use types were similar tothose for dry NH3 deposition fluxes and the resulting sea-sonal changes were sometimes significant except at northernurban sites (Fig 6c)

Dry pNH+4 deposition fluxes peaked in spring or summerat urban and rural sites but remained at similar levels acrossthe four seasons at background sites however no significantseasonal variations were found at any land use types exceptfor rural sites in the north (Fig 6d) Dry pNOminus3 depositionfluxes were higher in spring and winter than in summer andautumn at all land use types and the seasonal changes were

sometimes significant at background sites and at southern ur-ban and rural sites (Fig 6e) Total dry N deposition fluxes atall land use types showed similar seasonal variations to dryNH3 deposition with the highest values in summer and thelowest in winter significant seasonal differences generallywere observed between winter and the other three seasons(Fig 6f)

Wetbulk deposition fluxes of NH+4 -N NOminus3 -N and TINall showed significant seasonal variation at urban and ruralsites but not at background sites with the highest values insummer and the lowest in winter (Fig 7andashc)

37 Spatialndashtemporal variability in total annual dryand wetbulk deposition of Nr species

In eastern China total annual mean N deposition (dry pluswetbulk) fluxes at rural and background sites were compa-rable (on average 443plusmn 30 and 343plusmn 07 kg N haminus1 yrminus1

respectively) but significantly lower than those at urban sites(597plusmn 61 kg N haminus1 yrminus1 Table 2 and Fig S5 Supple-

Figure 6 Seasonal mean dry deposition averaged over 2011ndash2015 of (a) NH3 (b) NO2 (c) HNO3 (d) pNH+4 (e) pNOminus3 and (f) total Nrie the sum of all measured Nr in air at different land use types in eastern China and its northern and southern regions Sp Su Au and Wirepresent spring summer autumn and winter respectively U R and B denote urban rural and background sites respectively The numberof sites for each land use type in each region can be found in Table 2 The error bars are the standard errors of means and values withoutsame letters on the bars denote significant differences between the seasons (p lt 005)

ment) Similar tendencies for total N deposition fluxes wereobserved in the southern region while in the north a sig-nificant difference was only found between urban and back-ground sites (Fig S5 Supplement) From 2011 to 2015 nosignificant annual trend was found in the total N depositionat 16 selected sites (Fig S6a Supplement) The total annualmean N deposition fluxes at three land use types showedsmall and non-significant reductions (1ndash5 ) between 2011ndash2012 and 2013ndash2015 (Fig S6b Supplement) Regionally thetotal fluxes at each land use type were of similar magnitudein the two periods Also the ratio of NHx (wetbulk NH+4 -Ndeposition plus dry deposition of NH3 and particulate NH+4 )to NOy (wetbulk NOminus3 -N deposition plus dry deposition ofNO2 HNO3 and particulate NOminus3 ) showed a non-significantannual trend across all sites (Fig 8a) At all land use typesthe averaged ratios were slightly higher in the 2013ndash2015 pe-riod than in the 2011ndash2012 period (Fig 8b)

4 Discussion

41 Comparisons of NH3 and NO2 measurements withsatellite data

Eastern China is a highly industrialized and polluted regionand has been proven to be a hotspot of Nr (NH3 and NOx)emissions and deposition globally (Vet et al 2014 Kanaki-dou et al 2016) The results presented above showed thatin eastern China annual mean concentrations of measuredNr species in air and precipitation were generally higher inthe north than in the south (Table 1) This is likely due tohigher consumption of energy and application of N fertil-izers along with lower precipitation amounts in the northpreviously identified as key factors affecting spatial patternsof N deposition in China (Liu et al 2013 Jia et al 2014Zhu et al 2015) Because only 27 sites covering a range ofland use types were included in the present study additionalinformation would be valuable in determining whether theobserved spatial patterns adequately represent conditions ineastern China To address this issue we use measured NH3

Figure 7 Seasonal mean wetbulk deposition averaged over 2011-2015 of NH+4 (a) NOminus3 (b) and total inorganic N (TIN) ie the sum ofNH+4 and NOminus3 (c) in precipitation at different land use types in eastern China and its northern and southern regions Sp Su Au and Wirepresent spring summer autumn and winter respectively U R and B denote urban rural and background sites respectively The numberof sites for each land use type in each region can be found in Table 2 The error bars are the standard errors of means and values withoutsame letters on the bars denote significant differences between the seasons (p lt 005)

Figure 8 Annual trend of the ratio of NHx (wetbulk NH+4 -N de-position plus dry deposition of NH3 and particulate NH+4 ) to NOy

(wetbulk NOminus3 -N deposition plus dry deposition of NO2 HNO3and particulate NOminus3 ) across 16 selected sites (a) with a compar-ison between the 2011ndash2012 period and the 2013ndash2015 period fordifferent land use types in eastern China (b) U R and B denoteurban rural and background sites respectively The number of siteswith the same land use type can be found in Fig S6 in the Supple-ment

and NO2 concentrations to evaluate remote sensing tech-niques for retrieving NH3 and NO2 concentrations If accu-rate these remote sensing techniques are well suited to ascer-

tain regional species distributions NH3 and NOx are primaryemissions with important anthropogenic emissions (Fowleret al 2013) NO the main component of emitted NOx isoxidized in the atmosphere to NO2 NO2 is further oxidizedvia daytime or nighttime chemistry to HNO3 (Khoder 2002)NH3 and HNO3 can react to form fine particle ammoniumnitrate (Seinfeld and Pandis 2006) Thus spatial patterns ofNH3 and NO2 observed from space can be useful indicatorsof reduced and oxidized Nr pollution over eastern China

From satellite observations (Fig 9a b) it can be seen thatboth IASI_NH3 and OMI_NO2 columns show clearly highervalues over the northern region of eastern China Overallsatellite observations and surface measurements for NH3 andNO2 (plotted on the maps of Fig 9a b) show a similar spa-tial pattern Significant positive correlations were found be-tween IASI_NH3 column observations and NNDMN_NH3measurements (r = 072 p lt 0001 Fig 9c) and betweenOMI_NO2 observations and NNDMN_NO2 measurements(r = 086 p lt 0001 Fig 9d) at the 27 surface measurementlocations suggesting that satellite measurements of NH3 andNO2 can be used to capture regional differences in NH3 andNO2 pollution Looking beyond the surface measurement lo-cation the satellite observations further confirm the existenceof greater Nr pollution in the northern region of eastern Chinathan in the southern region

To further explore temporal concentration variabilitymonthly mean satellite NH3 and NO2 columns are compared

Figure 9 Spatial variation of atmospheric Nr in eastern China (a) NNDMN_NH3 concentrations vs IASI_NH3 columns (b) NNDMN_NO2concentrations vs OMI_NO2 columns (c) relationship of NNDMN_NH3 concentrations vs IASI_NH3 columns (d) relationship ofNNDMN_NO2 concentrations vs OMI_NO2 columns

with monthly mean ground concentrations of NH3 and NO2(Figs S7 and S8 Supplement) The linear correlation be-tween satellite columns and surface NH3 concentrations issignificant (p lt 005) at the 10 sites (r = 032ndash087) in thenorthern region and at 4 sites (r = 046ndash084) in the south-ern region (Fig S7 Supplement) while the linear correlationbetween satellite columns and surface NO2 concentrationsis significant at the 10 sites (r = 028ndash068) in the north-ern region and 9 sites (r = 036ndash066) in the southern re-gion (Fig S8 Supplement) These results indicate that theOMI_NO2 retrieval can well capture the temporal variationsof surface NO2 concentrations over eastern China whereasthe IASI_NH3 retrievals better capture temporal variabilityin surface concentrations for the northern region The weakcorrelations observed between IASI_NH3 observations andsurface measurements at 10 of the 14 sites in the southern re-gion (Fig S7 Supplement) suggest that the IASI_NH3 obser-vations need to be improved for investigating temporal vari-ability in NH3 concentration despite the satellite observa-tion being at a specific time of day that is while the surfaceconcentrations integrate across the diurnal cycle of emissionsand mixing layer evolution It should be noted that a directcomparison between surface concentration and satellite col-umn measurements is inevitably affected by many factorssuch as changes in boundary layer height vertical profiles

of species and interferences from cloud and aerosol (VanDamme et al 2015) Nevertheless the ratio of satellite col-umn to surface concentration measurements is meaningful asit can provide insight into sensitivity of a satellite retrieval tovariation in the concentration of a gas in the surface layer(Meng et al 2008) To make a more accurate comparisonthe vertical profile is recommended to convert the columnsto the ground concentrations in future work

42 Seasonal variations of Nr concentration anddeposition

The seasonal concentrations of Nr species in air and pre-cipitation are dependent on their sources and meteorologi-cal conditions The highest concentrations of NH3 in sum-mer at all land use types (Fig 3a) are most likely due to en-hanced NH3 emissions from natural and fertilized soils andbiological sources such as humans sewage systems and or-ganic waste in garbage containers (Chang et al 2016 Menget al 2018) Zhang et al (2018) showed that NH3 emis-sions in China show a strong summer peak with emissionsabout 50 higher in summer than spring and autumn Thelowest concentrations of NH3 in winter (Fig 3a) can beascribed to low NH3 volatilization under cold conditionshigh snow coverage and less agricultural activity (Cao etal 2009) with large consumption of NH3 to form NH4NO3

and (NH4)2SO4 The lower NO2 concentration in summer(Fig 3b) might result from higher atmospheric mixing in adeeper boundary layer and a higher rate of oxidation of NO2to HNO3 by reaction with OH (Atkins and Lee 1995) whichis more abundant in summer due to greater photochemicalactivity Increased NO2 emissions from greater coal combus-tion for domestic heating (from middle November to middleMarch) in northern China may also enhance NOx emissionsand subsequent NO2 concentrations in autumnwinter (Zhaoet al 2011)

Particulate NH+4 and NOminus3 are mainly generated viachemical reactions between NH3 and inorganic acids (egHNO3 H2SO4) We found that concentrations of pNH+4 andpNOminus3 at all land use types usually peaked in winter be-cause low temperature and high emissions of NOx and SO2are favourable for formation of NH4NO3 and (NH4)2SO4aerosols (Xu et al 2016) consistent with higher concen-trations of pNH+4 and pNOminus3 In addition in winter tem-perature inversions in combination with stable meteorolog-ical conditions (eg low wind speed) limit horizontal andvertical exchange of pollutants and further elevated atmo-spheric pNH+4 and pNOminus3 levels (F Liu et al 2017) In or-der to identify potential transport of NO2 pNH+4 and pNOminus3from northern region we calculated 3-day backward trajec-tories arriving at five southern sites (Nanjing Baiyun Tao-jing Ziyang and Huinong) during January April July andOctober using the TrajStat The TrajStat analysis generallyshowed that the high proportions (overall 10ndash36 ) of airmasses from the north to the south of eastern China occurredin the autumnwinter suggesting that the transport of NO2pNH+4 and pNOminus3 from northern China would result in in-creases in their respective concentrations in autumnwintersouth of the Qinling MountainsndashHuaihe River line except atZiyang site (Fig S9 Supplement)

Nitric acid is a secondary pollutant formed through gas-phase reaction of NO2 with the OH radical reaction ofNO3 with aldehydes or hydrocarbons or hydrolysis of N2O5(Khoder 2002) Nitric acid concentrations are expected to befurther influenced by air temperature relative humidity andambient NH3 concentrations (Allen et al 1989) fine particleNH4NO3 formation is favoured at low temperatures and highrelative humidities Due to a lack of information regardingprimary formation pathways and influencing factors at ourstudy sites we cannot offer a definitive explanation for smalland differing seasonal patterns of HNO3 concentrations ob-served at the three land use types (Fig 3c)

Ammonium-N and nitrate-N in precipitation mainly orig-inate from corresponding reduced (eg NH3 pNH+4 ) andoxidized (eg HNO3 NO2 pNOminus3 ) N in air scavenged re-spectively by rain andor snow events (Seinfeld and Pandis2006) At all land use types the seasonal variation of NH+4 -N concentration in precipitation was opposite that of reducedN concentrations (the sum of NH3 and pNH+4 Figs 4a andS10a in the Supplement) whereas a similar seasonal pat-tern was found between NOminus3 -N and oxidized N (the sum of

HNO3 NO2 and pNOminus3 ) concentrations (Figs 4b and S10bin the Supplement) Higher precipitation amounts in summercould account for lower NH+4 -N concentrations in summer(Figs 4a and S11 in the Supplement) due to a dilution effect(Xu et al 2015) In contrast seasonal variations of rainwa-ter NOminus3 -N concentrations were more likely dominated byseasonal changes in oxidized N concentrations rather thanprecipitation amount

The seasonal variation of NH3 dry deposition is generallysimilar to that of NH3 concentration (Figs 3a and 6a) Givencomparable seasonal mean Vd for NH3 across the four sea-sons in most cases (Fig S12andashc Supplement) the season-ality of NH3 deposition is mainly dominated by changes inambient NH3 concentrations Seasonal deposition fluxes ofNO2 and HNO3 both differ appreciably (Fig 6b c) showingsimilar variation to seasonality of their respective Vd values(Fig S12dndashi Supplement) Given weaker seasonal fluctua-tions of NO2 and HNO3 concentrations the seasonality ofNO2 and HNO3 dry deposition are primarily functions ofchanges in Vd Similar analyses suggest that seasonal vari-ation of pNOminus3 dry deposition was mainly caused by differ-ences in seasonal pNOminus3 concentrations (Figs 3e and 6e)whereas that of pNH+4 dry deposition was primarily drivenby seasonal changes in Vd (Figs 6c and S12jndashl Supplement)

43 The role of NH3 in mitigation of Nr air pollution

The latest pollutant emissions statistics from the ChineseMinistry of Environmental Protection (httpwwwzhbgovcngkmlhbbqt201507t20150722_307020htm) showedthat total annual emissions of SO2 and NOx were respec-tively reduced by 129 and 86 in 2014 (approximately99 and 63 Tg S yrminus1 respectively) compared with those in2010 (approximately 113 and 69 Tg S yrminus1 respectively)This suggests that the goal set for the 12th FYP period wasfulfilled ahead of time Our field measurements demonstratethat annual mean concentrations of each Nr species andtotal Nr did not show significant decreasing trends at mostsites during the 2011ndash2015 period (Fig S1andashf Supplement)Furthermore annual mean total Nr concentrations showednon-significant increases (1ndash16 ) at three land use typesduring the 2013ndash2015 period compared with 2011ndash2012(Fig 2f) These results together suggest that Nr pollutionmay be not effectively mitigated in eastern China duringthe 12th FYP likely due to the absence of NH3 regulationsdespite enforcement of a ldquoZero Increase Action Planrdquo by theMinistry of Agriculture for national fertilizer use (Liu et al2016)

Ammonia is the primary alkaline gas in the atmosphereIt plays an important role in formation of (NH4)2SO4 andNH4NO3 aerosols (Seinfeld and Pandis 2006) These sec-ondary inorganic aerosols account for 40ndash57 of the PM25concentrations in eastern China (Yang et al 2011 Huanget al 2014) Based on monthly mean molar concentrationsthere were significant positive linear correlations between

NH3 and pNH+4 NO2 and pNOminus3 SO2 and pSO2minus4 pNH+4

and pNOminus3 and pNH+4 and pSO2minus4 at all land use land

types except for a non-significant relationship of NH3 withpNH+4 at background sites (Fig 10andashe) These results sug-gest that the precursor gases are responsible for the formationof secondary inorganic ions (ie pNH+4 pNOminus3 and pSO2minus

4 )locally at urban and rural sites while secondary inorganicions at background sites likely originated from long-distancetransport The ratio of concentrations of NH3 to NHx (NH3plus pNH+4 ) at urban (053plusmn 015) and rural (052plusmn 016)sites exceeded values at background (043plusmn 016) sites Ac-cording to Walker et al (2004) a value greater than 05 in-dicates that NHx is more likely to be from local sources asopposed to long-range transport

It is known that NH3 in the atmosphere is preferentiallyneutralized by H2SO4 to form (NH4)2SO4 andor NH4HSO4with any remainder available for potential reaction withHNO3 to form NH4NO3 At urban and rural sites monthlymean pNH+4 concentrations significantly positively corre-lated with the sum of p2SO2minus

4 and pNOminus3 concentrations(Fig 10f) However the slopes of regression equations be-tween them were both smaller than unity (035 and 046 aturban and rural sites respectively) indicating an incompleteneutralization of acidic species (HNO3 and H2SO4) by NH3at urban and rural sites In other words NH3 is a factor limit-ing the formation of secondary inorganic ions A model sim-ulation by Wang et al (2011) found that without NH3 emis-sion controls NOminus3 in PM25 will be enhanced by 10 in2030 compared with 2005 in China despite improved NOx

emissions controls As reported by Zhang et al (2017) to-tal NH3 emissions in China increased from 121 Tg N yrminus1 in2000 to 156 Tg N yrminus1 in 2015 at an annual rate of 19 Incontrast total emissions of NOx and SO2 have decreased orstabilized in recent years and were estimated to be 84 and125 Tg S yrminus1 in 2014 respectively (Xia et al 2016) Basedon these factors implementation of NH3 control strategiestogether with more stringent NOx and SO2 emission con-trols should be considered to mitigate atmospheric Nr pollu-tion

44 The role of NH3 emissions in control of Ndeposition

The present results showed that total dry N deposition fluxesat three land use types were higher in the northern region ofeastern China than in the southern region (Table 1) mainlydue to higher NH3 dry deposition resulting from higher NH3concentrations in the north This is especially true for north-ern rural sites (Table 1) mostly located in the North ChinaPlain (NCP see details in Xu et al 2015) The NCP (thatis the plain areas in Beijing Tianjin Hebei Henan andShandong provinces) a highly populated region with inten-sive agricultural production contributes 30ndash40 of the to-tal annual NH3 emissions in China (Huang et al 2012) Inaddition higher NH3 concentration is also likely due to the

higher NH3 volatilization in calcareous soils than that in theacidic red soil as mentioned in Sect 21 Total annual NH3emissions in northern region increased from 43 Tg N yrminus1

in 2011 to 47 Tg N yrminus1 in 2015 at an annual rate of 18 In contrast the emissions of NOx and SO2 averaged 28and 37 Tg S yrminus1 during 2011ndash2015 and decreased at an-nual rates of 68 and 57 respectively (details of the emis-sions will be illustrated in Sect 45) Such reductions mayenhance free NH3 in the atmosphere However according toa modelling study by Han et al (2017) the influence of re-moving anthropogenic SO2 emissions on dry N depositionfluxes during 2010ndash2014 was quite weak with the changewithin simminus05 to sim 05 (kg N haminus1 yrminus1) over most regionsin China Thus we anticipate that reducing NH3 emissionscan effectively control N deposition

To further examine contributions of NH3 emissions to to-tal (wet plus dry) N deposition at each site and over east-ern China we conducted model sensitivity tests using thenested GEOS-Chem atmospheric chemistry model drivenby the GEOS-5 assimilated meteorological fields at a hor-izontal resolution of 12times 23 The model used anthro-pogenic emissions from the Multi-Resolution Emission In-ventory of China (MEIC httpmeicmodelorg) for the year2010 except for NH3 emissions that are taken from the Re-gional Emission in Asia (REAS-v2) inventory (Kurokawa etal 2013) with an improved seasonality derived by Zhaoet al (2015) The total NH3 and NOx emissions from eachsource over eastern China and its contribution to total emis-sions in China are presented in Table S13 in the SupplementThe NH3 and NOx emissions over eastern China are 116and 85 Tg N yrminus1 in 2010 which respectively account for90 and 89 of their total emissions over China Agriculturalsources including fertilizer use and livestock comprise mostof the NH3 emissions while fuel combustion activities in-cluding industry power plant and transportation contributemost of the NOx emissions and small amounts of NH3 emis-sions Both NH3 and NOx have natural sources (includinglightning biomass burning and soil emissions) but they arenegligible compared to anthropogenic emissions over easternChina Details of the model emissions and mechanisms havebeen described elsewhere (Zhao et al 2017 Xu et al 2018)

We evaluate the model simulations by comparison withmeasured bulk (both NH+4 -N and NOminus3 -N) fluxes The modelbiases for bulk NH+4 -N and NOminus3 -N deposition were 23 andminus23 respectively (Fig S13 Supplement) These biases arereasonable given uncertainties in Nr emissions and predic-tions of meteorology Given that model evaluation is not cen-tral to this work we presented the details in Sect S2 in theSupplement As shown in Fig 11 fertilizer use is the dom-inant source of total N deposition at all sites with contri-butions between 16 and 50 Also over eastern China thelargest contribution was from fertilizer use (36 ) relative tolivestock (10 ) industry (14 ) power plant (11 ) trans-portation (9 ) and other sources (20 the sum of contri-butions from human waste residential activities soil light-

Figure 10 Correlations of monthly mean molar concentrations of (a) pNH+4 vs NH3 (b) pNOminus3 vs NO2 (c) pSO2minus4 vs SO2 (d) pNOminus3

vs pNH+4 (e) pNH+4 vs pSO2minus4 (f) pNH+4 vs (p2SO2minus

4 + pNOminus3 ) at three land use types in eastern China The number of sites with thesame land use type in each region can be found in Table 1

ing and biomass burning) These results indicate that reduc-ing NH3 emissions by use of appropriate fertilization pat-terns (eg 4R technologies right amount right time rightform and right application technique Ju et al 2009) shouldbe a priority in curbing N deposition in eastern China Thisconclusion to some extent is supported by increased ratios ofreduced to oxidized N in the total deposition at three land usetypes (Fig 8b) as the major anthropogenic source of reducedN is mainly affected by NH3 volatilized from animal excre-ment and the application of nitrogenous fertilizers in agricul-ture Absence of NH3 emission controls may be the main rea-son for a small and non-significant change in the total N de-

position between 2011ndash2012 and 2013ndash2015 (Fig S6 Sup-plement) despite enforcement of stringent emission controlson NOx and SO2 To test the importance of future NH3 emis-sion control strategies we conducted separate model simula-tions which reduced NH3 emissions from fertilizer use by20 The results show that a 20 reduction in fertilizerNH3 emissions can lead to 74 decrease in total N depo-sition over eastern China

45 Deposition response to emission change

Similar to Nr concentrations there were no significant de-creasing trends in dry and bulk deposition of total N or of in-

Figure 11 Fractional contributions to total N deposition from emission sectors (ie fertilizer use livestock industry power plant transporta-tion and others including emissions from human waste residential activities soil lighting and biomass burning) at the 27 sites and overeastern China

dividual Nr species at almost all study sites (Figs S3 and S4Supplement) In addition we found that changes in annualmean deposition fluxes of various Nr species are fairly smallbetween the 2013ndash2015 and 2011ndash2012 periods (Fig 5)These results suggest that current emission controls did noteffectively reduce N deposition in eastern China

To further assess the relationship between emission anddeposition change we considered the emissions of SO2NOx and NH3 affecting the 16 study sites with contin-uous and simultaneous dry and bulk deposition measure-ments (Fig S6 and Table S1 Supplement) The regional NH3emission data for 2011ndash2015 were derived from Zhang etal (2017) while SO2 and NOx emission data for 2011ndash2014were derived from Xia et al (2016 emission data for the year2015 were provided by Yu Zhao and were unpublished) Wecompared these annual data with annual mean deposition val-ues from the 16 sites It should be noted that such assessmentis subject to some uncertainty as emission data were esti-mated based on the areas belonging to eastern China

A clear decreasing trend in SO2 and NOx emissions wasobserved with reductions of 32 and 25 in 2015 comparedto 2011 respectively (Fig 12a b) This reduction is directlyrelated to the widespread use of selective catalytic reduction

and flue gas de-sulfurization on power plants and industries(Van der A et al 2017) and to a lesser extent to the intro-duction of new emission standards for cars (Liu et al 2016)In contrast NH3 emissions generally showed a gradual in-creasing trend between 2011 and 2015 (Fig 12c) as con-trol strategies have not yet been enacted and implementedfor NH3 emissions in China

Regarding N deposition a non-significant increasingtrend was found for NHx (slope= 036 kg N haminus1 yrminus1)between the 2011 and 2015 period whereas NOy de-position exhibited a non-significant decreasing trend(slope= 054 kg N haminus1 yrminus1) Also there were non-significant linear correlations between NHx deposition andNH3 emissions and between NOy deposition and NOx

emissions This is not surprising given that atmosphericchemistry is complex and often behaves non-linearly (Fowleret al 2007 Fagerli and Aas 2008) Interactions between thedifferent pollutants precipitation variability and changes inthe relative amounts and lifetimes of the chemical speciesand in gasndashparticle partitioning all may contribute to thelack of correlation between emission and deposition trendsNon-linearities between emission and deposition changehave been described also elsewhere (Aguillaume et al

Figure 12 Emissions of SO2 (a) NOx (b) and NH3 (c) obtained asaverage data from the areas belonging to eastern China comparedwith deposition (dep) values in the same periods (mean values fromthe 16 sites showing in Fig S6 and Table S1 in the Supplement5-year averages)

2016 Karlsson et al 2011) Deposition in eastern China isalso influenced by emissions from outside the region furtherdegrading any expected correlation with local emissions

46 Uncertainties and limitations

The present study examined annual trends of concentrationsof Nr species in air and precipitation as well as dry andbulk N deposition based on Kendall tests and only five an-nual data values (2011ndash2015) Although the test can use asfew as four data points indications of statistically significanttrends for data sets are unlikely to be truly representative ofthe trends that are actually occurring due to in the short du-ration of the measurement data set Longer time series (egmore than 10 years) will likely allow detection of more sig-nificant time trends in future work Another uncertainty mayarise from the fact that we used fixed monthly mean dry de-position velocities of gaseous and particulate Nr species forthe same months from June 2013 to December 2015 Nev-ertheless the uncertainty in the Vd value did not largely af-

fect the deposition trend as the annual trend in dry deposi-tion of Nr species is more likely driven by changes in am-bient Nr concentrations than by changing deposition veloci-ties as evident from fairly low standard deviations of annualmean Vd of Nr species at our selected 27 sites between 2008and 2012 (sim 0029 for NH3 sim 0005 for NO2 sim 0054 forHNO3 and sim 0019 for both pNH+4 and pNOminus3 data wereextracted from Zhao et al 2017)

In addition we did not account for inter-annual changesin meteorology which also strongly influences atmosphericNr levels and N deposition (Xu et al 2015 2017) For ex-ample air concentrations of NO2 NH3 pNH+4 and pNOminus3tend to increase under the relatively stagnant conditions priorto a cold frontrsquos arrival and decrease substantially after thecold front brings precipitation and strong winds into the re-gion (Xu et al 2017) On the inter-annual timescale thefrequency of cold front passage may be affected by large-scale circulation patterns such as the position of the SiberianHigh for eastern China (Jia et al 2015) For example alarge inter-annual variation in precipitation amount was ob-served at the selected 16 sites during 2011ndash2015 (Fig S14Supplement) which partially lead to inter-annual changes inwetbulk N deposition However given that in situ measure-ments of other meteorological variables (eg air temperaturerelative humidity air pressure wind speed and direction) arenot available and that GEOS-5 assimilated meteorologicalfields were updated after May 2013 an evaluation of the ef-fect of meteorology on Nr concentration and deposition isrecommended for future work

Uncertainties also exist in the source attribution calculatedwith the GEOS-Chem simulations since results largely de-pend on the emission inventories fed to the model Zhao etal (2017) pointed out that uncertainties in current NH3 emis-sions inventories (eg large range of emission values in cur-rent studies and absence of bi-directional NH3 exchange be-tween the land and atmosphere) may influence nitrogen de-position simulation in China Future work based on improvedNH3 emission inventories (eg Zhang et al 2018) and in-cluding bidirectional ammonia exchange with the surface isessential to better examine source attribution of N depositionin China

5 Conclusion

We have characterized spatial and temporal (annual and sea-sonal) variations in concentrations and deposition of majorNr species in air (NH3 NO2 HNO3 pNH+4 and pNOminus3 )and precipitation (NH+4 -N and NOminus3 -N) for three land usetypes (eg urban rural and background) in eastern China byexamining 5-year (2011ndash2015) in situ measurements at 27sites We further examined regional features of Nr pollutionby comparison of satellite and surface measurements of NH3and NO2 and examined the sources of total N deposition overthe whole region for the year 2010 using the GEOS-Chem

model at horizontal resolution of 12times 23 Our major re-sults and conclusions are as follows

In eastern China annual mean concentrations and dryand bulk deposition fluxes of measured Nr species inair and precipitation generally ranked in the order ur-ban gt rural gt background The air concentrations and dry de-position were usually higher at all land use types in the north-ern region of eastern China than in the southern region es-pecially (except HNO3) at rural sites for which the differ-ences reached statistically significant levels This is also truefor the annual VWM concentrations of NH+4 -N NOminus3 -N andTIN in precipitation whereas bulk deposition fluxes of thesespecies were comparable for matched land use types betweenthe northern and southern regions

No significant trends in the annual mean concentrationsand dry and bulk deposition fluxes of measured Nr species inair and precipitation were observed at almost all sites dur-ing the 2011ndash2015 period Also annual averages of thesevalues showed non-significant changes between the 2011ndash2012 and 2013ndash2015 periods for all land use types Ambienttotal concentrations of measured Nr species showed a non-significant seasonal variation at all land use types whereasindividual Nr species exhibited a significant seasonal vari-ation in most cases except for NO2 and pNH+4 at urbansites and HNO3 at all land use types Unlike air concentra-tions dry deposition of total Nr showed consistent and sig-nificant seasonal variation for each land use type with thehighest values in summer and the lowest values in winterThe Vd was a dominant factor influencing seasonal variationsof NO2 HNO3 and pNH+4 concentrations while seasonalvariations of NH3 and pNOminus3 are mainly influenced by theirrespective air concentrations The concentrations of NH+4 -N NOminus3 -N and TIN in precipitation showed significant sea-sonal variations ranking in the consistent order of win-ter gt spring gt autumnasymp summer Also significant seasonalvariations in bulk deposition were also found following theconsistent order of summer gt springasymp autumn gt winter

Both IASI satellite-retrieved NH3 columns and OMIsatellite-retrieved NO2 columns over eastern China showedhigher values in the north than in the south In additionsignificant positive correlations were found between mea-sured NH3 concentrations and retrieved NH3 columns andbetween measured NO2 concentrations and columns Theseresults together reveal that atmospheric Nr pollution is moreserious in the northern region and also suggest that satel-lite retrievals of NH3 and NO2 columns can provide usefulinformation on spatial concentration variability of these twokey Nr species at a regional or national scale Weak correla-tions between IASI_NH3 observations and surface NH3 mea-surements were found at most selected sites suggesting thatIASI_NH3 observations in their current state are not as read-ily used to accurately track temporal variability in surfaceNH3 concentrations

Ammonia is currently not included in Chinarsquos emissioncontrol policies of air pollution precursors although the ne-

cessity of mitigation has been the subject of discussion dur-ing recent years Across all urban and rural sites the slopesof the regression relation between pNH+4 and the sum ofpSO2minus

4 and pNOminus3 were both smaller than unity indicatingthat controlling NH3 emissions not only can directly reduceambient NH3 concentrations but also lower the formationof pNH+4 and pNOminus3 Fertilizer use contributed 36 of thetotal N deposition over eastern China suggesting reducingNH3 emissions from fertilizer application would be an effec-tive strategy for reducing N deposition Overall our findingsreveal persistent serious Nr pollution during the 12th FYPperiod despite implementation of current emission controlsand highlight the importance of NH3 emission controls formitigating future atmospheric Nr concentrations and deposi-tion in eastern China

Data availability The data used in this study are available from thecorresponding author upon request (liu310caueducn)

The Supplement related to this article is availableonline at httpsdoiorg105194acp-18-10931-2018-supplement

Author contributions XJL FZ and WX designed the researchWX XSL JS and LLu conducted the field work LLi XZ andMC prepared IASI_NH3 and OMI_NO2 products YHZ and LZconducted model simulations XZ and BG provided the ammoniaemission data YZ provided the emission data of nitrogen dioxideand sulfur dioxide WX LLi MC YL and YHZ performed the dataanalysis and prepared the figures and tables WX and XJL wrote thepaper with comments from JLC ZF and YP

Competing interests The authors declare that they have no conflictof interest

Acknowledgements This study was supported by the National KeyRampD Program of China (2017YFC0210101 2017YFC02101062014BC954202) the National Natural Science Foundation ofChina (41705130 41425007 31421092) as well as the NationalTen-thousand Talents Program of China (Xuejun Liu) The authorsthank all staff at the study sites (listed in Table S1 Supplement)for their cooperation during sample collection We also thanktwo anonymous reviewers for insightful comments regarding theimprovement of the paper

Leiming ZhangReviewed by two anonymous referees

References

Aguillaume L Rodrigo A and Avila A Long-term effects ofchanging atmospheric pollution on throughfall bulk deposition

and streamwaters in a Mediterranean forest Sci Total Environ544 919ndash928 httpsdoiorg101016jscitotenv2015120172016

Allen A G Harrison R M and Erisman J W Field measure-ments of the dissociation of ammonium nitrate and ammoniumchloride aerosols Atmos Environ 23 1591ndash1599 1989

Atkins D H F and Lee D S Spatial and temporal variation of ru-ral nitrogen dioxide concentrations across the United KingdomAtmos Environ 29 223ndash239 1995

Bobbink R Hicks K Galloway J Spranger T Alkemade RAshmore M Bustamante M Cinderby S Davidson E andDentener F Global assessment of nitrogen deposition effectson terrestrial plant diversity a synthesis Ecol Appl 20 30ndash592010

Boersma K F Eskes H J Veefkind J P Brinksma E J vander A R J Sneep M van den Oord G H J Levelt P FStammes P Gleason J F and Bucsela E J Near-real timeretrieval of tropospheric NO2 from OMI Atmos Chem Phys7 2103ndash2118 httpsdoiorg105194acp-7-2103-2007 2007

Cao J J Zhang T Chow J C Watson J G Wu F and LiH Characterization of atmospheric ammonia over Xirsquoan ChinaAerosol Air Qual Res 9 277ndash289 2009

Chang Y H Liu X J Deng C R Dore A J and Zhuang G SSource apportionment of atmospheric ammonia before duringand after the 2014 APEC summit in Beijing using stable nitro-gen isotope signatures Atmos Chem Phys 16 11635ndash11647httpsdoiorg105194acp-16-11635-2016 2016

Dammers E Palm M Van Damme M Vigouroux C Smale DConway S Toon G C Jones N Nussbaumer E WarnekeT Petri C Clarisse L Clerbaux C Hermans C Lutsch EStrong K Hannigan J W Nakajima H Morino I HerreraB Stremme W Grutter M Schaap M Wichink Kruit R JNotholt J Coheur P F and Erisman J W An evaluation ofIASI-NH3 with ground-based Fourier transform infrared spec-troscopy measurements Atmos Chem Phys 16 10351ndash10368httpsdoiorg105194acp-16-10351-2016 2016

Erisman J W Grennfelt P and Sutton M The European per-spective on nitrogen emission and deposition Environ Int29 311ndash325 httpsdoiorg101016S0160-4120(02)00162-92003

Fagerli H and Aas W Trends of nitrogen in air and pre-cipitation model results and observations at EMEP sitesin Europe 1980ndash2003 Environ Pollut 154 448ndash461httpsdoiorg101016jenvpol200801024 2008

Fenn M E Baron J S Allen E B Rueth H M Ny-dick K R Geiser L Bowman W D Sickman J OMeixner T Johnson D W and Neitlich P Ecologi-cal Effects of Nitrogen Deposition in the Western UnitedStates BioScience 53 404ndash420 httpsdoiorg1016410006-3568(2003)053[0404EEONDI]20CO2 2003

Fowler D Smith R Muller J Cape J N Sutton M ErismanJ W and Fagerli H Long term trends in sulphur and nitrogendeposition in Europe and the cause of non-linearities Water AirSoil Pollut 7 41ndash47 httpsdoiorg101007s11267-006-9102-x 2007

Fowler D Coyle M Skiba U Sutton M A Cape J N ReisS Sheppard L J Jenkins A Grizzetti B Galloway J NVitousek P Leach A Bouwman A F Butterbach-Bahl KDentener F Stevenson D Amann M and Voss M The

global nitrogen cycle in the twenty-first century Philos T RSoc B 368 20130164 httpsdoiorg101098rstb201301642013

Fuzzi S Baltensperger U Carslaw K Decesari S van DerGon H D Facchini M C Fowler D Koren I LangfordB Lohmann U Nemitz E Pandis S Riipinen I RudichY Schaap M Slowik J G Spracklen D V Vignati EWild M Williams M and Gilardoni S Particulate matterair quality and climate lessons learned and future needs At-mos Chem Phys 15 8217ndash8299 httpsdoiorg105194acp-15-8217-2015 2015

Galloway J N Townsend A R Erisman J W Bekunda MCai Z Freney J R Martinelli L A Seitzinger S P andSutton M A Transformation of the Nitrogen Cycle Recenttrends questions and potential solutions Science 320 889ndash892httpsdoiorg101126science1136674 2008

Ge B Z Wang Z F Xu X B Wu J B Yu X Land Li J Wet deposition of acidifying substances in dif-ferent regions of China and the rest of East Asia model-ing with updated NAQPMS Environ Pollut 187 10ndash21httpsdoiorg101016jenvpol201312014 2014

Gilbert R O Statistical methods for environmental pollution mon-itoring John Wiley amp Sons 1987

Gu B J Sutton M A Chang S X Ge Y and JieC Agricultural ammonia emissions contribute to Chinarsquosurban air pollution Front Ecol Environ 12 265ndash266httpsdoiorg10189014WB007 2014

Guo S Hu M Zamora M L Peng J F Shang D J ZhengJ Du Z F Wu Z J Shao M and Zeng L M Elucidatingsevere urban haze formation in China P Natl Acad Sci USA111 17373 httpsdoiorg101073pnas1419604111 2014

Han X Zhang M G Skorokhod A and Kou X XModeling dry deposition of reactive nitrogen in Chinawith RAMS-CMAQ Atmos Environ 166 47ndash61httpsdoiorg101016jatmosenv201707015 2017

He N P Zhu J X and Wang Q F Uncertainty and perspec-tives in studies of atmospheric nitrogen deposition in China Aresponse to Liu et al (2015) Sci Total Environ 520 302ndash304httpsdoiorg101016jscitotenv201503063 2015

Huang P Zhang J B Xin X L Zhu A N Zhang C Z MaD H Zhu Q G Yang S and Wu S J Proton accumula-tion accelerated by heavy chemical nitrogen fertilization and itslong-term impact on acidifying rate in a typical arable soil in theHuang-Huai-Hai Plain J Integr Agric 14 148ndash157 2015

Huang R J Zhang Y Bozzetti C Ho K F Cao J J Han YDaellenbach K R Slowik J G Platt S M Canonaco F Zot-ter P Wolf R Pieber S M Bruns E A Crippa M CiarelliG Piazzalunga A Schwikowski M Abbaszade G Schnelle-Kreis J Zimmermann R An Z Szidat S Baltensperger UEl Haddad I and Prevot A S High secondary aerosol contri-bution to particulate pollution during haze events in China Na-ture 514 218ndash222 httpsdoiorg101038nature13774 2014

Huang X Song Y Li M M Li J F Huo Q Cai X H ZhuT Hu M and Zhang H S A high-resolution ammonia emis-sion inventory in China Global Biogeochem Cy 26 GB1030httpsdoiorg1010292011GB004161 2012

Ianniello A Spataro F Esposito G Allegrini I Rantica EAncora M P Hu M and Zhu T Occurrence of gas phase

ammonia in the area of Beijing (China) Atmos Chem Phys 109487ndash9503 httpsdoiorg105194acp-10-9487-2010 2010

Jia B Wang Y Yao Y and Xie Y A new indicator on the im-pact of large-scale circulation on wintertime particulate matterpollution over China Atmos Chem Phys 15 11919ndash11929httpsdoiorg105194acp-15-11919-2015 2015

Jia Y L Yu G R He N P Zhan X Y Fang H JSheng W P Zuo Y Zhang D Y and Wang Q F Spa-tial and decadal variations in inorganic nitrogen wet deposi-tion in China induced by human activity Sci Rep 4 3763httpsdoiorg101038srep03763 2014

Jia Y L Yu G R Gao Y N He N P Wang Q F Jiao C Cand Zuo Y Global inorganic nitrogen dry deposition inferredfrom ground and space-based measurements Sci Rep 6 19810httpsdoiorg101038srep19810 2016

Ju X T Xing G X Chen X P Zhang S L Zhang L J LiuX J Cui Z L Yin B Christie P Zhu Z L and Zhang FS Reducing environmental risk by improving N management inintensive Chinese agricultural systems P Natl Acad Sci USA106 3041ndash3046 httpsdoi101073pnas0902655106 2009

Kanakidou M Myriokefalitakis S Daskalakis N andFanourgakis G Past present and future atmospheric ni-trogen deposition J Atmos Sci 73 160303130433005httpsdoiorg101175JAS-D-15-0278s1 2016

Karlsson G P Akselsson C Hellsten S and KarlssonP E Reduced European emissions of S and N effectson air concentrations deposition and soil water chem-istry in Swedish forests Environ Pollut 159 3571ndash3582httpsdoiorg101016jenvpol201108007 2011

Khoder M I Atmospheric conversion of sulfur dioxide to particu-late sulfate and nitrogen dioxide to particulate nitrate and gaseousnitric acid in an urban area Chemosphere 49 675ndash684 2002

Krotkov N A Mclinden C A Li C Lamsal L N CelarierE A Marchenko S V Swartz W H Bucsela E J JoinerJ Duncan B N Boersma K F Veefkind J P Levelt P FFioletov V E Dickerson R R He H Lu Z F and StreetsD G Aura OMI observations of regional SO2 and NO2 pollu-tion changes from 2005 to 2015 Atmos Chem Phys 16 4605ndash4629 httpsdoiorg105194acp-16-4605-2016 2016

Kurokawa J Ohara T Morikawa T Hanayama S Janssens-Maenhout G Fukui T Kawashima K and Akimoto HEmissions of air pollutants and greenhouse gases over Asian re-gions during 2000ndash2008 Regional Emission inventory in Asia(REAS) version 2 Atmos Chem Phys 13 11019ndash11058httpsdoiorg105194acp-13-11019-2013 2013

Li H Zhang Q Zheng B Chen C Wu N Guo H ZhangY Zheng Y Li X and He K Nitrate-driven urban hazepollution during summertime over the North China Plain At-mos Chem Phys 18 5293ndash5306 httpsdoiorg105194acp-18-5293-2018 2018

Li Y Niu S and Yu G Aggravated phosphorus limita-tion on biomass production under increasing nitrogen load-ing a meta-analysis Global Change Biol 22 934ndash943httpsdoiorg101111gcb13125 2016

Liang X Zou T Guo B Li S Zhang H Z Zhang S YHuang H and Chen S X Assessing Beijingrsquos PM25 pollu-tion severity weather impact APEC and winter heating Proc RSoc A 471 20150257 httpsdoiorg101098rspa201502572015

Liu F Beirle S Zhang Q van der A R J Zheng B TongD and He K NOx emission trends over Chinese cities es-timated from OMI observations during 2005 to 2015 AtmosChem Phys 17 9261ndash9275 httpsdoiorg105194acp-17-9261-2017 2017

Liu L Zhang X Y Zhang Y Xu W Liu X J ZhangX M Feng J L Chen X R Zhang Y H Lu X HWang S Q Zhang W T and Zhao L M Dry particulatenitrate deposition in China Environ Sci Techno 51 5572httpsdoiorg101021acsest7b00898 2017a

Liu L Zhang X Xu W Liu X Li Y Lu X Zhang Y andZhang W Temporal characteristics of atmospheric ammoniaand nitrogen dioxide over China based on emission data satelliteobservations and atmospheric transport modeling since 1980 At-mos Chem Phys 17 9365ndash9378 httpsdoiorg105194acp-17-9365-2017 2017b

Liu X J Duan L Mo J M Du E Z Shen J LLu X K Zhang Y Zhou X B He C E andZhang F S Nitrogen deposition and its ecological impactin China An overview Environ Pollut 159 2251ndash2264httpsdoiorg101016jenvpol201008002 2011

Liu X J Zhang Y Han W X Tang A Shen JL Cui Z L Vitousek P Erisman J W GouldingK Christie P Fangmeier A and Zhang F S En-hanced nitrogen deposition over China Nature 494 459ndash462httpsdoiorg101038nature11917 2013

Liu X J Vitousek P Chang Y H Zhang W F Mat-son P and Zhang F S Evidence for a historic changeoccurring in China Environ Sci Technol 50 505ndash506httpsdoiorg101021acsest5b05972 2016

Lu C Q and Tian H Q Spatial and temporal patterns of nitrogendeposition in China Synthesis of observational data J GeophysRes 112 D22S05 httpsdoiorg1010292006JD0079902007

Lu C Q and Tian H Q Half-century nitrogen deposition in-crease across China A gridded time-series data set for re-gional environmental assessments Atmos Environ 97 68ndash74httpsdoiorg101016jatmosenv201407061 2014

Marchetto A Rogora M and Arisci S Trend analysis of atmo-spheric deposition data A comparison of statistical approachesAtmos Environ 64 95ndash102 2013

Meng Z Y Xu X B Wang T Zhang X Y Yu X L Wang SF Lin W L Chen Y Z Jiang Y A and An X Q Ambientsulfur dioxide nitrogen dioxide and ammonia at ten backgroundand rural sites in China during 2007ndash2008 Atmos Environ 442625ndash2631 2008

Meng Z Y Xu X B Lin W L Ge B Z Xie Y L Song BJia S H Zhang R Peng W Wang Y Cheng H B YangW and Zhao H Role of ambient ammonia in particulate ammo-nium formation at a rural site in the North China Plain AtmosChem Phys 18 167ndash184 httpsdoiorg105194acp-18-167-2018 2018

MEPC (Ministry of Environmental Protection of the Peoplersquos Re-public of China) Report on Environmental Quality in China2010 available at httpjcsmepgovcnhjzlzkgb2010zkgb201106t20110602_211579htm last access 3 June 2011

Miyazaki K Eskes H Sudo K Boersma K F Bowman Kand Kanaya Y Decadal changes in global surface NOx emis-sions from multi-constituent satellite data assimilation Atmos

Chem Phys 17 807ndash837 httpsdoiorg105194acp-17-807-2017 2017

Pan Y P Wang Y S Tang G Q and Wu D Wet and dry depo-sition of atmospheric nitrogen at ten sites in Northern China At-mos Chem Phys 12 6515ndash6535 httpsdoiorg105194acp-12-6515-2012 2012

Pan Y P Wang Y S Zhang J K Liu Z R Wang L L TianS L Tang G Q Gao W K Ji D S and Song T Redefin-ing the importance of nitrate during haze pollution to help op-timize an emission control strategy Atmos Environ 141 197ndash202 httpsdoiorg101016jatmosenv201606035 2016

Pinder R W Walker J T Bash J O Cady-Pereira K E HenzeD K Luo M Z Osterman G B and Shephard M W Quan-tifying spatial and seasonal variability in atmospheric ammoniawith in situ and space-based observations Geophys Res Lett38 L04802 httpsdoiorg1010292010GL046146 2011

Russell A R Valin L C and Cohen R C Trends in OMINO2 observations over the United States effects of emissioncontrol technology and the economic recession Atmos ChemPhys 12 12197ndash12209 httpsdoiorg105194acp-12-12197-2012 2012

Salmi T Maatta A Anttila P Ruoho-Airola T and Amnell TDetecting trends of annual values of atmospheric pollutants bythe MannndashKendall test and Senrsquos slope estimates ndash the Excel tem-plate application MAKESENS Publications on Air Quality No31 Finnish Meteorological Institute Helsinki Finland 2002

Seinfeld J H and Pandis S N Atmospheric chemistry andphysics from air pollution to climate change 2nd Edn WileyInterscience New Jersey 2006

She W Hu Huanyong father of Chinarsquos population geographyChina Popul Today 15 1ndash20 1998

Souri A H Choi Y Jeon W Woo J-H Zhang Q andKurokawa J-i Remote sensing evidence of decadal changes inmajor tropospheric ozone precursors over East Asia J GeophysRes 122 2474ndash2492 httpsdoiorg1010022016JD0256632017

Tang Y S Simmons I van Dijk N Di Marco C Ne-mitz E Dammgen U Gilke K Djuricic V Vidic Sand Gliha Z European scale application of atmospheric re-active nitrogen measurements in a low-cost approach to inferdry deposition fluxes Agr Ecosyst Environ 133 183ndash195httpsdoiorg101016jagee200904027 2009

Theil H A Rank-Invariant Method of Linear and PolynomialRegression Analysis in Henri Theilrsquos Contributions to Eco-nomics and Econometrics edited by Raj B and Koerts JAdvanced Studies in Theoretical and Applied EconometricsSpringer Netherlands 345ndash381 1992

Tian S L Pan Y P Liu Z R Wen T X and WangY S Size-resolved aerosol chemical analysis of ex-treme haze pollution events during early 2013 in ur-ban Beijing China J Hazard Mater 279 452ndash460httpsdoiorg101016jjhazmat201407023 2014

Van Damme M Clarisse L Dammers E Liu X Nowak JB Clerbaux C Flechard C R Galylacaux C Xu W andNeuman J A Towards validation of ammonia (NH3) measure-ments from the IASI satellite Atmos Meas Tech 8 1575ndash1591 httpsdoiorg105194amt-8-1575-2015 2015

van der A R J Mijling B Ding J Koukouli M E Liu F LiQ Mao H and Theys N Cleaning up the air effectiveness

of air quality policy for SO2 and NOx emissions in China At-mos Chem Phys 17 1775ndash1789 httpsdoiorg105194acp-17-1775-2017 2017

Vet R Artz R S Carou S Shaw M Ro C-U Aas W BakerA Bowersox V C Dentener F Galy-Lacaux C Hou APienaar J J Gillett R Forti M C Gromov S Hara HKhodzher T Mahowald N M Nickovic S Rao P S Pand Reid N W A global assessment of precipitation chemistryand deposition of sulfur nitrogen sea salt base cations organicacids acidity and pH and phosphorus Atmos Environ 93 3ndash100 httpsdoiorg101016jatmosenv201310060 2014

Walker J T Whitall D R Robarge W and Paerl H W Ambi-ent ammonia and ammonium aerosol across a region of variableammonia emission density Atmos Environ 38 1235ndash12462004

Wang G H Zhang R Y Gomez M E Yang L X ZamoraM L Hu M Lin Y Peng J F Guo S Meng J J Li JJ Cheng C L Hu T F Ren Y Q Wang Y S Gao JCao J J An Z S Zhou W J Li G H Wang J Y TianP F Marrero-Ortiz W Secrest J Du Z F Zheng J ShangD J Zeng L M Shao M Wang W G Huang Y WangY Zhu Y J Li Y X Hu J X Pan B W Cai L ChengY T Ji Y M Zhang F Rosenfeld D Liss P S Duce RA Kolb C E and Molina M J Persistent sulfate formationfrom London Fog to Chinese haze P Natl Acad Sci USA 11313630 httpsdoiorg101073pnas1616540113 2016

Wang S X Xing J Jang C R Zhu Y Fu J Sand Hao J M Impact assessment of ammonia emissionson inorganic aerosols in East China using response surfacemodeling technique Environ Sci Techno 45 9293ndash9300httpsdoiorg101021es2022347 2011

Wen L Chen J M Yang L X Wang X F Xu C H SuiX Yao L Zhu Y H Zhang J M Zhu T and WangW X Enhanced formation of fine particulate nitrate at a ru-ral site on the North China Plain in summer The importantroles of ammonia and ozone Atmos Environ 101 294ndash302httpsdoiorg101016jatmosenv201411037 2015

Wesely M L Parameterization of surface resistances to gaseousdry deposition in regional-scale numerical-models Atmos Env-iron 23 1293ndash1304 1989

Whitburn S Van Damme M Clarisse L Bauduin S Heald CL Hadji-Lazaro J Hurtmans D Zondlo M A Clerbaux Cand Coheur P F A flexible and robust neural network IASINH3retrieval algorithm J Geophys Res-Atmos 121 6581ndash6599httpsdoiorg1010022016JD024828 2016

Xia Y M Zhao Y and Nielsen C P Benefits of Chinarsquos effortsin gaseous pollutant control indicated by the bottom-up emis-sions and satellite observations 2000ndash2014 Atmos Environ136 43ndash53 httpsdoiorg101016jatmosenv2016040132016

Xu W Luo X S Pan Y P Zhang L Tang A H Shen J LZhang Y Li K H Wu Q H Yang D W Zhang Y Y XueJ Li W Q Li Q Q Tang L Lu S H Liang T Tong YA Liu P Zhang Q Xiong Z Q Shi X J Wu L H ShiW Q Tian K Zhong X H Shi K Tang Q Y Zhang LJ Huang J L He C E Kuang F H Zhu B Liu H JinX Xin Y J Shi X K Du E Z Dore A J Tang S CollettJr J L Goulding K Sun Y X Ren J Zhang F S andLiu X J Quantifying atmospheric nitrogen deposition through

a nationwide monitoring network across China Atmos ChemPhys 15 12345ndash12360 httpsdoiorg105194acp-15-12345-2015 2015

Xu W Wu Q H Liu X J Tang A H Dore A J and Heal MR Characteristics of ammonia acid gases and PM25 for threetypical land-use types in the North China Plain Environ SciPollut Res 23 1158ndash1172 httpsdoiorg101007s11356-015-5648-3 2016

Xu W Song W Zhang Y Liu X Zhang L Zhao Y Liu DTang A Yang D Wang D Wen Z Pan Y Fowler D Col-lett Jr J L Erisman J W Goulding K Li Y and Zhang FAir quality improvement in a megacity implications from 2015Beijing Parade Blue pollution control actions Atmos ChemPhys 17 31ndash46 httpsdoiorg105194acp-17-31-2017 2017

Xu W Zhao Y H Liu X J Dore A J ZhangL Liu L and Cheng M Atmospheric nitrogen de-position in the Yangtze River basin Spatial patternand source attribution Environ Pollut 232 546ndash555httpsdoiorg101016jenvpol201709086 2018

Yang F Tan J Zhao Q Du Z He K Ma Y Duan F ChenG and Zhao Q Characteristics of PM25 speciation in repre-sentative megacities and across China Atmos Chem Phys 115207ndash5219 httpsdoiorg105194acp-11-5207-2011 2011

Yang Y H Li P He H L Zhao X Datta A Ma WH Zhang Y Liu X J Han W X Wilson M C andFang J Y Long-term changes in soil pH across major for-est ecosystems in China Geophys Res Lett 42 933ndash940httpsdoiorg1010022014GL062575 2015

Zhang L Chen Y F Zhao Y H Henze D K Zhu L YSong Y Paulot F Liu X J Pan Y P and Huang B XAgricultural ammonia emissions in China reconciling bottom-up and top-down estimates Atmos Chem Phys 18 339ndash355httpsdoiorg105194acp-18-339-2018 2018

Zhang L M Gong S L Padro J and Barrie L Asize-segregated particle dry deposition scheme for an at-mospheric aerosol module Atmos Environ 35 549ndash560httpsdoiorg101016s1352-2310(00)00326-5 2001

Zhang Q Duan F K He K B Ma Y L Li HY Kimoto T and Zheng A H Organic nitrogen inPM25 in Beijing Front Environ Sci Eng 9 1004ndash1014httpsdoiorg101007s11783-015-0799-5 2015

Zhang X M Wu Y Y Liu X J Reis S Jin J X DragositsU Damme Van M Clarisse L Whitburn S and Co-heur P F Ammonia emissions may be substantially under-estimated in China Environ Sci Technol 51 12089ndash12096httpsdoiorg101021acsest7b02171 2017

Zhao Y Nielsen C P Lei Y McElroy M B and Hao JQuantifying the uncertainties of a bottom-up emission inven-tory of anthropogenic atmospheric pollutants in China AtmosChem Phys 11 2295ndash2308 httpsdoiorg105194acp-11-2295-2011 2011

Zhao Y Zhang L Pan Y Wang Y Paulot F and HenzeD K Atmospheric nitrogen deposition to the northwestern Pa-cific seasonal variation and source attribution Atmos ChemPhys 15 10905ndash10924 httpsdoiorg105194acp-15-10905-2015 2015

Zhao Y Zhang L Chen Y F Liu X J Xu WPan Y P and Duan L Atmospheric nitrogen depo-sition to China a model analysis on nitrogen budgetand critical load exceedance Atmos Environ 153 32ndash40httpsdoiorg101016jatmosenv201701018 2017

Zhu J X He N P Wang Q F Yan G F Wen D Yu GR and Jia Y L The composition spatial patterns and influ-encing factors of atmospheric wet nitrogen deposition in Chi-nese terrestrial ecosystems Sci Total Environ 511 777ndash785httpsdoiorg101016jscitotenv201412038 2015

Abstract

Introduction

Materials and methods

Study area and site descriptions

Field sampling and chemical analysis

Deposition estimate

Satellite retrievals of NH3 and NO2

Statistical analysis

Results

Spatial variability in concentrations of Nr species in air and precipitation

Annual variability in concentrations of Nr species in air and precipitation

Seasonal variability in concentrations of Nr species in air and precipitation

Spatial variability in dry and wetbulk N deposition of Nr species

Annual variability in dry and wetbulk N deposition

Seasonal variability in dry and wetbulk deposition of Nr species

Spatial--temporal variability in total annual dry and wetbulk deposition of Nr species

Discussion

Comparisons of NH3 and NO2 measurements with satellite data

Seasonal variations of Nr concentration and deposition

The role of NH3 in mitigation of Nr air pollution

The role of NH3 emissions in control of N deposition

Deposition response to emission change

Uncertainties and limitations

Conclusion

Data availability

Author contributions

Competing interests

Acknowledgements

References

and wetbulk N deposition at almost all of the selected sitesA lack of significant changes in annual averages between the2013ndash2015 and 2011ndash2012 periods for all land use types sug-gests that any effects of current emission controls are not yetapparent in Nr pollution and deposition in the region Ambi-ent concentrations of total Nr exhibited non-significant sea-sonal variation at all land use types although significant sea-sonal variations were found for individual Nr species (egNH3 NO2 and pNOminus3 ) in most cases In contrast dry depo-sition of total Nr exhibited a consistent and significant sea-sonal variation at all land use types with the highest fluxes insummer and the lowest in winter Based on sensitivity testsby the GEOS-Chem model we found that NH3 emissionsfrom fertilizer use (including chemical and organic fertiliz-ers) were the largest contributor (36 ) to total inorganic Nrdeposition over eastern China Our results not only improvethe understanding of spatialndashtemporal variations of Nr con-centrations and deposition in this pollution hotspot but alsoprovide useful information for policy-makers that mitigationof NH3 emissions should be a priority to tackle serious Ndeposition in eastern China

1 Introduction

In China and globally human activities have dramaticallyincreased emissions of nitrogen oxides (NOx =NO+NO2)and ammonia (NH3) into the atmosphere since the beginningof the industrial revolution (Galloway et al 2008 Liu et al2013) NOx and NH3 emitted into the atmosphere are trans-formed to nitrogen-containing particles (eg particulate NH+4and NOminus3 and organic nitrogen Ianniello et al 2010 Zhanget al 2015) which are major chemical constituents of air-borne PM25 (particulate matter with a diameter of 25 microm orless) and have implications for air quality and climate (Fuzziet al 2015) As a result of elevated reactive nitrogen (Nr)emissions nitrogen (N) deposition through dry and wet pro-cesses has also substantially increased over China (Liu et al2013 Lu et al 2007 2014 Jia et al 2014 2016) and exces-sive deposition of N has resulted in detrimental impacts in-cluding decreased biological diversity (Bobbink et al 2010)nutrient imbalance (Li et al 2016) increased soil acidifica-tion (Yang et al 2015) and eutrophication of water bodies(Fenn et al 2003) Furthermore Nr-associated haze pollu-tion episodes characterized by high concentrations of PM25occur frequently in China as evidenced in particular in 2013(Guo et al 2014 Huang et al 2014 Tian et al 2014)

In order to control its notorious air pollution China hasreduced national emissions of SO2 and particulate matterby 14 and 30 respectively from 2005 to 2010 (MEPC2011) Additionally stringent measures (eg using selectivecatalyticnon-catalytic reduction systems and implementingtighter vehicle emission standards) were implemented dur-ing the 12th Five Year Plan (FYP) period (2011ndash2015) with

aims to reduce 2015 annual emissions of SO2 and NOx by8 and 10 respectively relative to 2010 levels (Xia et al2016) However there is as yet no regulation or legislationthat deals with national NH3 emissions and thus the emis-sion reductions of SO2 and NOx used to achieve desiredair-quality improvement goals will be compromised (Gu etal 2014) Significant increases in PM25 concentrations havebeen observed in the years 2013 and 2014 as compared to2012 excluding the influence of meteorological conditionson inter-annual variations (Liang et al 2015) Other stud-ies with more conclusive evidence have likewise suggestedthat NH3 plays a vital role in sulfate formation and exacer-bates severe haze pollution development in urban regions ofChina (Wang et al 2016) even acting as the key limitingfactor for the formation of secondary inorganic aerosol (Wuet al 2016) In addition due to higher local and regionalconcentrations of NH3 in the atmosphere nitrate-driven hazepollution occurred during summertime in urban environmentin the North China Plain (Li et al 2018) The absolute andrelative concentrations of particulate nitrate in urban Beijingincreased with haze development (Pan et al 2016) Alsonitrate contributed to a large fraction of the elevated PM25concentrations at a rural site in the North China Plain andhigh NH3 in the early morning accelerated the formation offine nitrates (Wen et al 2015)

High rates of N deposition have also been observed dur-ing 2011ndash2014 across China (Xu et al 2015) However todate no study based on long-term ground-based observa-tions has provided any information on the effectiveness ofSO2 and NOx emission controls on N deposition in ChinaNon-linearities have been identified between reductions inemissions and deposition in Europe over the last 3 decades(Aguillaume et al 2016 Fowler et al 2007) Due to thetightly coupled yet complex relationship between emissionsconcentrations and deposition long-term monitoring net-works can test the effectiveness of emission controls (Eris-man et al 2003) Currently two national N deposition net-works are operational in China ie the Nationwide NitrogenDeposition Monitoring Network (NNDMN Liu et al 2011Xu et al 2015) and the Chinese Ecosystem Research Net-work (CERS Zhu et al 2015) The NNDMN containing43 in situ monitoring sites has been measuring wet N depo-sition and ambient concentrations of five major Nr species(ie gaseous NH3 NO2 and HNO3 and particulate NH+4and NOminus3 ) since 2010 the latter species for subsequent esti-mation of dry deposition The CERS was established in 1988and has been mainly focused on wet N deposition at 41 fieldstations In addition to ground-based measurements satelliteobservations enable retrieval of atmospheric NH3 and NO2with high temporal and spatial resolutions (Dammer et al2016 Russell et al 2012) providing a means to reveal spa-tial distributions and long-term trends of ambient NH3 andNO2 levels at regional to global scales and also to evaluatethe effectiveness of emission controls (Krotkov et al 2016)However to effectively use the vast satellite data sets for en-

3 Results

BKD 47 57 10 51 24 188 18 15 33(n= 2) (06) (03) (01) (02) (03) (01) (02) (03) (01)

4 Discussion

5 Conclusion

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

3 Results

BKD 47 57 10 51 24 188 18 15 33(n= 2) (06) (03) (01) (02) (03) (01) (02) (03) (01)

4 Discussion

5 Conclusion

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

3 Results

BKD 47 57 10 51 24 188 18 15 33(n= 2) (06) (03) (01) (02) (03) (01) (02) (03) (01)

4 Discussion

5 Conclusion

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

3 Results

BKD 47 57 10 51 24 188 18 15 33(n= 2) (06) (03) (01) (02) (03) (01) (02) (03) (01)

4 Discussion

5 Conclusion

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

3 Results

BKD 47 57 10 51 24 188 18 15 33(n= 2) (06) (03) (01) (02) (03) (01) (02) (03) (01)

4 Discussion

5 Conclusion

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

BKD 47 57 10 51 24 188 18 15 33(n= 2) (06) (03) (01) (02) (03) (01) (02) (03) (01)

4 Discussion

5 Conclusion

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

4 Discussion

5 Conclusion

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

4 Discussion

5 Conclusion

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

4 Discussion

5 Conclusion

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

4 Discussion

5 Conclusion

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

4 Discussion

5 Conclusion

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

5 Conclusion

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

5 Conclusion

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

5 Conclusion

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

5 Conclusion

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

5 Conclusion

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

5 Conclusion

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

5 Conclusion

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

Abstract

Introduction



Deposition estimate



Results








Discussion







Conclusion

Data availability


Competing interests

Acknowledgements

References

Documents

Spatial–temporal patterns of inorganic nitrogen air … · 2020. 7. 31. · 10932 W. Xu et al.: Spatial–temporal patterns of inorganic nitrogen air concentrations and wet/bulk