Analysis of polluted air masses effecting the area P.O ...€¦ · Analysis of polluted air masses effecting the area ... 26.7 km (Nestl), 8.9 km (Nest2), cr-system with 15 vertical

Analysis of polluted air masses effecting the area

of Eastern Germany during a SANA episode

H. Feldmann,* A. Ebel/ H. Mass,*" M. Memmesheimer,*

HJ. Jakobs*

"University of Cologne, Insitutefor Geophysics and Meteorology

EURAD Project, 50923 Cologne, Germany

F̂raunhofer Institute for Atmospheric Environmental Reasearch,

P.O. Box 1343, 82467 Garmisch-Partenkirchen, Germany

Abstract

The regional air pollution model system EURAD has been applied to aSANA special observation period in August/September 1991. The trans-port pathways and distances of polluted air masses are analysed using tra-jectories calculated from the predicted fields of the meteorological mesoscalemodel MM5 - a part of the EURAD system.

Furthermore the regional budget of ozone for East Germany is calcu-lated using mesoscale chemistry transport simulations. The dynamical andchemical processes which are responsible for the generation and removal ofincreased photooxidant concentrations are discussed.

1 Introduction

Under summerly high pressure conditions periods of elevated oxidant levelsfrequently occur in Central Europe. In many cases the concentrations ofozone and its precursors increase throughout several days. These periodsare usually terminated by the arrival of clean air masses.

Such an episode is simulated with the European Acid Deposition modelEURAD. The model calculations are performed as a contribution to theSANA project, which deals with the air pollution situation over easternGermany. EURAD supplies mesoscale simulations of the meteorological andchemical conditions on an European scale for the SANA special observationperiods.

One of the campaigns - called SANA3 - took place in August/September1991. The simulated period spans from 28 Aug. to 6 Sept. 1991. It includesa phase with an increase of oxidant levels (30 Aug. - 4 Sept., accumulationphase) followed by a sharp drop (afternoon of 4 Sept. until 6 Sept., removalphase) in the pollutant concentrations in Central Europe. Figure 1 showsthe calculated average ozone density over East Germany during SANA3.

Based on model calculations the pathways and chemical composition ofair masses entering eastern Germany are analysed. In addition the ba-

Transactions on Ecology and the Environment vol 6, © 1995 WIT Press, www.witpress.com, ISSN 1743-3541

96 Observation and Simulation of Air Pollution

lancing between dynamical and chemical processes is discussed. The studyis an extension of the investigation by Feldmann et al.* concentrating onsulfur budgets to photooxidants.

2 Description of the model

The EURAD modelling system contains three major modules: the PSU/NCAR meteorological Mesoscale Model (MM5), the EURAD EmissionModel (EEM) and the Chemical Transport Model (CTM), which has beenderived from the RADM model (Chang et al.̂ ). Table 1 gives an overviewover the modelling concept for this study. The model setup is described indetail by Jakobs et alA The modelling domain is shown in Figure 2.

Table 1. EURAD model concept for the episode SAN A3.Grell et aUx,y on a lambert conformal projection, Arakawa Bgrid spacing: 80 km (Coarse), 26.7 km (Nestl),8.9 km (Nest2),cr-system with 15 vertical layers up to 100 hPaEurope (Coarse), Central Europe (Nestl),East Germany (Nest2)time dependent, relaxationderived from ECMWF global analysis (T106)explicit4th order (interior grid)Blackadarexplicitlong- and short-wave radiation fluxes in the PELNewtonian relaxation against ECMWF analysis ofhorizontal Wind and Temperature (only coarse grid)2-way-interactive multiple nesting

MM5Grid

Model area

Initial andboundary conditions

Intergration techniqueHorizontal diffusionBoundary layerHydrological cycleRadiationData assimilation

Grid refinementCTMGrid and model areaLateral boundariesIntegration technique

Advection schemeVertical diffusionChemistryCloudsDry depositionGrid refinement

Hass et al.\ Hass et al.\ Chang et al.%as MM5, but Arakawa C gridinflow/outflowsymetrized operator splitting with different timesteps according to physical/chemical constraints4th order Bottdependent on PEL scaling parametersRADM2 with 63 species, 158 reactionsmodified RADM modulemodified RADM moduleseveral 1-way-nesting steps (Pleim et al/)

EEMInput dataGrid (Input)Components (Input)Transfer mat ionComponents

Biogenic emissions

Memmesheimer et al.EMEP European Emission inventory for 1991150 km x 150 kmSO*, NOx, CO, VOC by EMEP, NHZ by Asmanpopulation density weightingSOs, Sulfate, NO, NO^ CO, NH^several I/OC-classes according to RADM2-mechanismIsoprene and Terpenes (Liibkert & Schopp^)


Observation and Simulation of Air Pollution 97

I 30 I 31 I 01 I 02 I 03 I 04August/September 1991

I 05

50 60 70

Figure 1: Calculated average ozone density over East Germany. The solidline marks the average boundary layer height in that region.

3 Trajectory studies

To analyse the origin and pathways of the air masses which influence thearea of eastern Germany during the SANA3 episode trajectories are used.They are calculated using the meteorological fields predicted by the MM5.The meteorological conditions during the episode are described in detail byFeldmann et aU.

Backward trajectories over 96 hours starting at 12 UTC for four conse-cutive days between 3 and 6 September are given in Figure 2. The startingpoint is the measurement site Lindenberg - east of Berlin - at an approximateheight of 500 m well within the PBL (see Figure 1). They represent themeteorological situation during SANA3 in Central Europe.

3 Sept. 1991 Position and length of trajectory A in Figure 2 are represen-tative for the preceeding days of the episode. A high pressure system overthe Baltic Sea causes inflow from the east into eastern Germany. The trajec-tory ends over northern Scandinavia in the approximate height of 600 hpa(about 4 km). In an anticyclonic subsident motion the air parcel is trans-ported over Poland to the receptor point. The travelling height remainsabove 1500 m for most of the four days. So a significant uptake of anthro-pogenic emissions takes place only at the day before the arrival.4 Sept. 1991 On the next day the situation is slightly different (trajec-tory B). The air parcel still arrives Germany from the east, but the traveldistance is much shorter. The trajectory remains over the former USSR andPoland within the four days. Due to the lower height of this trajectory anenhanced uptake of emissions by the transported air mass is possible.



5 Sept. and 6 Sept. 1991 In the final phase of SANA3 the high pressureridge moves to the west and is centered north of Scotland. On its easternside colder moist air is transported from the northwest into Central Europe.The movement of the air parcels is much faster. The trajectories (C and D)reach the modelling domain between two and three days before the arrivalat Lindenberg. The travelling height is low, but the pathway over the oceancauses an inflow of very clean air into Germany. This change in the flowpattern provides the explanation for the drop in the ozone concentrationsover East Germany.From the beginning of the episode the temperatures increase from about

20°C up to 30°C on 4 September. After the frontal passage the temper-atures in eastern Germany remain below 20°C. There is no precipitationduring SANA3 over that area and therefore no wet deposition.

Time of ArrivalA 03.09.9112 UTCB 04.09.91 12 UTCC 05.09.9112 UTCD 06.09.91 12 UTC

Min. Pressure600 hPa700 hPa860 hPa900 hPa

Max. PressurelOOOhPa1000 hPa960 hPa980 hPa

Figure 2: EURAD modelling domain (coarse grid) and backward trajec-tories from the starting point Lindenberg. Starting height: 950 hPa. Thethicknes of the lines marks the altitude. The height range is individuallygiven for each trajectory.

4 The ozone budget and process analysis

ConceptThe CTM calculates the tendencies of the trace gas concentrations due to



several transport and transformation processes. Within this study thesetendencies are used to investigate which processes are responsible for theaccumulation and removal of photooxidants during SANA3. The method isdescribed in more detail by Feldmann et al.\

The following tendencies are taken into account:• horizontal and • vertical advective transport• vertical diffusion• cloud effects (which are vertical redistribution, liquid phase reactions,

wash- and rainout; radiative effects due to a change of photolysis ratesare considered within the chemistry tendency)

• gas phase chemistry• emissions (for the emitted species)• dry and • wet deposition

The sum of these tendencies represents the total change of trace gas con-centrations in a grid box.

The analysis is performed for the part of the model grid which covers thearea of East Germany. In the vertical the model layers up to about 3500 mare used to calculate a regional budget for a control volume which includesthe planetary boundary layer and a part of the lower free troposphere.

ResultsThe simulation of the SANA3 episode in August/September 1991 shows aperiod of increasing oxidant levels and photochemical activity under highpressure influence over eastern Germany (Figure 1).

Accumulation phase: The highest concentrations of ozone and its precur-sors occur at noon of 4 September 1991, just when the mean wind directionchanges from east to northwest.

The regional budget of ozone (Figure 3) shows that there are two ma-jor processes which increase the concentration levels during the accumula-tion phase: Vertical advection from above the control volume and daytimechemical production.

The major loss processes are: dry deposition, nighttime chemical de-struction and horizontal advection. The strong negative net contribution ofhorizontal transport to the budget indicates that East Germany acts as asource region for ozone during that period.

There are other processes which are important mainly for internal redis-tribution of the trace gases (Figure 4 a,b) :- There is a frequent occurrence of fairweather clouds in the upper part ofthe PEL mainly on the first days of the accumulation phase. Because ofthe relatively low cloud tops and a lack of precipitation throughout SANA3their contributions to the budget are low. But the clouds affect the verticaldistribution of the trace constituents. For instance at 11 UTC of 1 Septem-ber (Figure 4a) there is a downward transport of Os between 1500 m andthe near surface layers by the clouds.



1000 -

500

-500 ~

-1000 biI 30 I 31 I 01 I 02 I 03 I 04 I 05 I 06

August/September 1991

Figure 3: Trend of total ozone during SANA3 within the control volumefor East Germany and tendencies of the major source and loss processes.

3000

2500

,-,2000

|1500

1000

500

0

1. 9.9111UTC

+—+ horizontal advection*—* vertical advectionA—A vertical diffusionQ—0 clouds

gas phase chemistrytotal

3.9.9119UTC

Figure 4: Average vertical trend of the ozone density within the controlvolume with tendencies of the major processes. Part A (left): Time 1 Sept.11 UTC -daytime conditions. Part B (right): Time 3 Sept. 19 UTC - night-time conditions.

- The turbulent vertical diffusion has a strong diurnal cycle. In the noc-turnal boundary layer (Figure 4b) the mixing is limited to the lowest fewhundred meters. Whereas in the early afternoon hours the PEL reaches upto maximum heights of more than 2000 m. During daytime the trace gasesonly have weak vertical gradients (Figure 1) due to efficient boundary layer



mixing. Photochemical production provides the largest contribution to thebudget throughout the PEL (Figure 4a). In the evening when convectionvanishes a chemical residual layer is formed where pollutants are trappedfor the night, because of reduced mixing and weak chemical destruction.When the PEL raises in the morning these pollutants are fumigated againinto the mixing layer. Chemical loss is strongest at low altitudes during thenight where emissions of NO destroy ozone.

Removal phase: There are several reasons for the lower % density afterthe change of the mean flow direction on 4 September:- The polluted air is removed from eastern Germany to the south and tothe east by horizontal advection.- The influence of the high pressure system is reduced and there is less im-port from above by vertical advection.- Chemical production is reduced drastically because of the removal of pre-cursor substances and lower chemical activity due to a reduction of pho-tolysis rates by a dense cloud coverage and the lower temperatures. Thecomposition of the hydrocarbon and nitrogen mixture differs significantlybetween the phases of the episode. For instance the relative amount of theolefines, which have a great impact on the ozone concentration (Derwentand Jenkin™), is much lower within the removal phase compared to theaccumulation phase. This leads to further reduction of the chemical ozoneproduction.

5 Conclusions

The application of a complex 3-dimensional model as EURAD in an episodicstudy gives the opportunity to analyse the effects of the processes which areresponsible for the development of smog situations. Therefore the model isa suitable tool for a better understanding of the coupling between dynami-cal and chemical processes.

We have shown that advective transport provides the largest contribu-tion to the total ozone budget. However increase by vertical advection andloss by horizontal transport are in close balance during the acccumulationphase. Therefore the increase of the ozone mass during this photochemicalepisode is caused mainly by chemical production. For the removal phase areduced efficiency of the processes which increase ozone was found, whereasthe loss by horizontal transport is significantly enhanced.

For considerations regarding the evaluation of models applied to the sim-ulation of SANA episodes refer to Ebel et al.**.

Acknowledgement

The SANA project is financed by the Federal Ministry of Education,Science,Research and Technology (BMBF). EURAD is financed by theBMBF and the Ministry for Science and Research (MWF) of the fed-eral state Nordrhein — Westfalen, The numerical calculations have beensupported by the computing center (ZAM) of the Research Center Jiilich



(KFA) and were performed on a CRAY Y-MP. The DWD gave access to me-teorological analyses from the ECMWF. Emission data have been providedby EMEP, The GENEMIS subproject of EUROTRAC and W. Asman.

References

1. Feldmann, H., Hass, H., Memmesheimer, M. & Jakobs, H.J. Budgetsof atmospheric sulfur for eastern Germany based on mesoscalesimulations, submitted to Meteorologische Zeitschrift, 1995.

2. Chang, J.S., Brost, R.A., Isaksen, I.S.A., Madronich, S., Middleton, P.,Stockwell, W.R. & Walcek, C.J. A three-dimensional Eulerian aciddeposition model: physical concepts and formation, J. Geophys. Res.,92,14681 - 14700, 1987.

3. Jakobs, H.J., Feldmann, H., Hass, H. & Memmesheimer, M. The use ofnested models for air pollution studies: an application of the EURADmodel to a SANA episode, J. Appl. Met., in press, 1995.

4. Grell, G.A., Dudhia, J. & Stauffer, D.R. A description of the fifth gene-ration PENN STATE/NCAR MESOSCALE MODEL (MM5), NCAR/TN-398+IA, National Center for Atmospheric Research, Boulder, CO,117pp,1993.

5. Hass, H., Jakobs, H.J., Memmesheimer, M., Ebel, A. & Chang, J.S. Simu-lation of a wet deposition case in Europe using the European Acid Depo-position Model (EURAD), in Air Pollution Modeling and its ApplicationVIII (ed. H. van Dop and D.G. Steyn), pp 204-214, Plenum Press, NewYork, 1991.

6. Hass, H., Ebel, A., Feldmann, H., Jakobs, H.J. & Memmesheimer, M.Evaluation studies with a regional chemical transport model (EURAD)using air quality data from the EMEP monitoring network, Atmos.Environ., 27A, 867-887, 1993.

7. Pleim, J.E., Chang, J.S. & Zhang, K. A nested grid mesoscale at-mospheric chemistry model, J. Geophys. Res., 96, 3065-3084, 1991.

8. Memmesheimer, M., Tippke, J., Ebel, A., Hass, H., Jakobs, H.J. & Laube,M. On the use of EMEP emission inventories for European scale airpollution modelling with the EURAD model, in Proceedings of the EMEPEMEP Workshop on Photooxidant Modelling for Long-Range Transportin Relation to Abatement Strategies, Berlin, April 16-19, pp. 307-324,1991.

9. Liibkert, B. & Schopp, W. A model to calculate natural VOC emissionsfrom forests in Europe, IIASA WP-89-082, IIASA, Laxenburg, Austria,1989.

10. Derwent, R.G. & Jenkin, M.E. Hydrocarbons and the long-range trans-port of ozone and PAN across Europe, Atmos. Environ., 25A, 1661-1678, 1991.

11. Ebel, A., Feldmann, H., Fiedler, F., Jakobs, H.J., Klemm, O., Nester, K.,Schaller, E., Schwartz, A. & Werhahn, J. Contributions to the evaluationof chemical transport models within the SANA Project, this issue.


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Analysis of polluted air masses effecting the area P.O ...€¦ · Analysis of polluted air masses effecting the area ... 26.7 km (Nestl), 8.9 km (Nest2), cr-system with 15 vertical