Ground-based and satellite DOAS within QUITSAT project

I.Kostadinov, S.Masieri, A.Petritoli, M.Premuda, F.Ravegnani, D. Bortoli*, G.GiovanelliISAC-CNR, via Godetti,101, 40129 Bologna, Italy* GCE – University of Evora (CGE-UE), Portugal

In collaboration with

Carlo Gavazzi Space, ItalyDepartment of Electronics for Automation – University of Brescia, Italy

QUITSAT (www.quitsat.it) is an Italian pilot project funded by the Italian Space Agency - ASI - devoted to Air Quality (AQ) assessment through the fusion of observations coming from polar and geostationarysatellite sensors and ground-based data collected by DOAS spectrometry, multispectral solar radiometry, lidar techniques and chemical transport modeling.

The project (2006-2009),led by Carlo Gavazzi Space (Italy), consists 3 subsystems: Monitoring, Forecasting and Planning.

Monitoring: provides maps of NO2, SO2, O3, HCHO concentration at the ground together with estimates of VOC biogenic emissions through the fusion of gas tropospheric contents derived from SCIAMACHY/ENVISAT (OMI/AURA) and MOPITT/Terra observations, ground-based measurements, meteorological modeling and comparison with CTM modeling

One of the QUITSAT products, named QM3, is developed to estimate NO2, SO2, O3 and HCHO concentration at the ground level.

Objective:Generation of Maps of Air Quality Index (AQI) on the project domain.

QUITSAT project overview

The generation of NO2 maps includes:

Retrieving of NO2 tropospheric VCD from satellite measurements (SCIA), using our satellite data processor (QUITSAT v 1.0)

Integration of CTM and satellite observations to obtain ground level concentration of NO2

Retrieving of NO2 tropospheric VCD (zenith-sky DOAS) and ground level concentration (long-path DOAS)

Procedures for comparisons and validations aimed to guarantee the quality of the input data used for generation of the project output products. For this reason data provided by ARPA (Regional Environmental Agency) in-situ analyser network have been included into the analysis too.

Activities

2) The stratospheric contribution is removed by subtraction with a value obtained chosing atropospheric background region (i.e. over ocean) [Richter and Burrows, 2002]

3) The tropospheric vertical column is then retrieved with RTM used for AMF estimation [Palazzi, et al. 2005]

Satellite measurements of NO2 VCD

1) The DOAS methodology furnish the total slant column density

QUITSAT-v1.0 SCIA L1 � L2 data processed at ISAC-CNR, Bologna

AMF calculation

Air Mass Factor was calculated applying the PROMSAR multiple scattering model (Palazzi et al. 2005).

• The model has been run for different scenarios:- 5 levels of A.O.D.- seasonal climatic parameters- rural or urban environment are considered too

Satellite measurements of NO2 VCD

Satellite measurements of NO2 VCD

QUITSAT V2 and V3

OMI data processed by KNMI for retrieving oftropospheric NO2 column, available through www.temis.nl have been used within the second and third reаlise of the QUITSAT system.

Ground-based zenith-sky DOAS

Calculated partial tropospheric column is used to validate:

• modelled column over the stations. • Satellite tropospheric column

Mt. Cimone 44°11'N, 10°42' E, 2165 m a.s.l. Bologna 44°31' N, 11°20' E, 42 m a.s.l. - urban area SP Capofiume 44° 39'N, 11°39'E, 10 m a.s.l. - rural area

y = 1.3489x - 6E+15R2 = 0.7293

1.0E+15

6.0E+15

1.1E+16

1.6E+16

2.1E+16

2.6E+16

1E+15 6E+15 1.1E+16 1.6E+16 2.1E+16 2.6E+16

TCAM NO2 tvc (molec/cm2)

DO

AS

NO

2 tv

c (m

olec

/cm

2 )

NO2 (0÷2 km) tropospheric column as a difference between two DOAS measurements taken at different altitude.

Satellite & Ground - based zenith-sky DOAS: Time averaging

The partial tropospheric column exhibits significant variations under specific local scenarios. In such cases it is necessary to average obtained values over time interval τ before to be compared with the satellite measurements. The interval duration appears to be an important factor. Studies are ongoing in this regard, considering also:

- the FoV of the space-borne instrument- wind direction and velocity in respect to the subsatellite track.

2.00E+15

4.00E+15

6.00E+15

8.00E+15

1.00E+16

1.20E+16

1.40E+16

1.60E+16

1.80E+16

2.00E+16

12 12.5 13 13.5 14 14.5 15

Local time, h

NO

2 col

ona

trop

osf (

0-2k

m),

mol

ec/c

m2

7.58E15

6.68E15

OMI over-pass

τ1

τ2

Satellite & Ground-based zenith sky DOAS: Max distance

Bologna

1.00E+13

5.01E+15

1.00E+16

1.50E+16

2.00E+16

2.50E+16

3.00E+16

3.50E+16

0 50 100 150 200 250 300

MaxDist, km

NO

2 tv

c O

MI,

mol

ec/c

m2

04/02/200810/02/200816/02/200821/02/200824/02/200821/02/2008 Bologna station

The dimensions of the target area over which the satellite measurements are averaged before to be compared with the ground-based DOAS measurements need detailed consideration.Under pollution events (e.g. 04/2/2008, 21/2/2008, assuming increased NO2concentration near the borders of Bologna urban area) the enlarging of the target area leads to decreasing of the averaged NO2 column. For days with lower and uniform NO2 concentration the enlargement of the target is less critical.A test have been performed in respect to a virtual ground-based station placed at Ferrara (about 45 km Bologna). The increasing of the max distance leads to increasing of the standard deviation (e.g. 10/2/2009, Ferrara)

Ferrara

1.00E+13

5.01E+15

1.00E+16

1.50E+16

2.00E+16

2.50E+16

3.00E+16

3.50E+16

0 50 100 150 200 250 300Max Dist, km

NO

2 tvc

OM

I, m

olec

/cm

2

04/02/200810/02/200821/02/200824/02/200816/02/2008

Long-path DOAS

Long-path DOAS measurements have been performed during the field campaigns.

NO2 long-path DOAS measurements vs. in-situ measurements obtained during QUITSAT field campaigns. Only clear sky measurement are taken in this analysis

The main reason for the differences between both data series is considered resulting from the fact that two instruments couldn’t be placed very near each other. ARPA analyzer is operating at the city center of Bologna, while long-path DOAS instrument was installed at CNR area, which is in outskirt of Bologna.

ARPA in-situ network in the Bologna area and the ISAC institute.

ARPA, (Regional environmental agency), with more than 100 stations in Po Valley, perform Air Quality monitoring.

The ARPA in-situ network in Bologna area

GAMES [Volta et al., 2006], made by three modules:the multi-phase Eulerian 3D photochemical model TCAM (Transport Chemical Aerosol Model, [Carnevale et al., 2008];

the meteorological pre-processor PROMETEO

the emission processor POEMPM [Carnevale et al., 2006] specifically designed to produce present and alternative emission scenarios.

Po Valley has been horizontally subdivided into 64x48 pixels, with a resolution of 10km × 10km each. Vertical domain extends up to 3900m a.g.l., and is subdivided into 11 layers of growing thickness.

GAMES Model System

2 2S M

S M

S M

S M

CC

C CC C

C CC C

=

⎡ ⎤⎛ ⎞+⎢ ⎥⎜ ⎟⎜ ⎟∆ ∆⎢ ⎥⎝ ⎠⎣ ⎦

⎡ ⎤⎛ ⎞+⎢ ⎥⎜ ⎟

∆ ∆⎢ ⎥⎝ ⎠⎣ ⎦

iv) an average NO2 profile corresponding to the satellite ground pixel is calculated from the model simulations and the respective column is scaled so to be equal to CC obtaining then a corrected profile. The Ground Level concentration, thus corrected, is considered the output product (GLCNO2).

The procedure for merging satellite measurements and CTM simulations to get an improved ground level NO2 concentration, consists:

i) deriving of NO2 tropospheric column from satellite (CS) and its error (∆CS) applying DOAS technique;

ii) deriving of NO2 tropospheric column integrating the vertical profile from the GAMES model, considering all model pixels which center is within given satellite ground pixel - calculation of CM and ∆CM.

iii) Calculation of corrected column (CC)

Integration of modelled and satellite data

B

A

Example

Averaged [NO2] reffered to the period May 2007 - March 2008.

Modelled [NO2] at ground level

Integrated model & satellite data [NO2] at ground level

SCIA NO2 measurements

In-situ [NO2] vs. QM3 product

Comparison of integrated modelled & satellite NO2concentration at ground-level, (QUITSAT QM3 product ), vs. simultaneously in-situ data provided by ARPA over all the project domain. Result for the second realise of QUITSAT System

Vertically scanning DOAS

Test measurements with TropoGAS SpectrometerUV-Vis GASCOD type multi-input 290-700 nm spectral interval, resolution 0.5 nmMeasurement of Tropospheric NO2, SO2, O3, HCHO columns and profiles. Alt-azimuth scanner collecting diffuse solar radiation from previously selected angles of sight.

Vertical profiles in the first 2km of troposphere by means of Radiative transfer model, inversion method and DOAS analisys

Acquired valuable experience regarding integration of ground-based and satellite DOAS data with CTM model output aimed to Air Quality evaluation. Obtained results demonstrate the feasibility of thisapproach.

It is foreseen to enlarge the deployment of multi-axis (imaging) DOAS instruments for target gases profiling.

We are interested in to share our experience within joint research or application projects.

In the future activities the next ground-based DOAS stations could be introduced too:

Stara Zagora (Bulgaria) Accra (Ghana)Terra Nova Bay (Antarctic)

Conclusions and future applications

Acknowledgments

• The authors would like to thank ARPA Emilia Romagna and ARPA Lombardia for providing in situ measurements and CETEMPS (Center of Integration of remote sensing techniques and numerical modelling for the forecast of severe weather of University of L’Aquila) for the initial and boundary conditions from CHIMERE simulations.

• The authors would like also to thank TEMIS (TroposphericEmission Monitoring Internet Service) [http://www.temis.nl] to providing OMI level 2 data of NO2 tropospheric vertical column.

• The research has been developed in the framework of the Pilot Project QUITSAT (QUalità dell’aria mediante l’Integrazione di misure da Terra, da SAtellite e di modellistica chimica multifase edi Trasporto - contract I/035/06/0 – http://www.quitsat.it), sponsored and funded by the Italian Space Agency (ASI).

• The author Bortoli D. was financially supported by the Portuguese Science Foundation - FCT through grant SFRH/BPD/22160/2005

Refereces

• Palazzi E., A. Petritoli , G. Giovanelli, I. Kostadinov, D. Bortoli , and F. Ravegnani, 2005, PROMSAR: A multiple scattering atmospheric model for the analysis of DOAS remote sensing measurements, Adv. Space. Res., 36, 1007-1014.

• Petritoli A., Bonasoni P., Giovanelli G., Ravegnani F., Kostadinov I.,Bortoli D., Weiss A., Schaub D., Richter A. and F. Fortezza, 2004, First comparison between ground-based and satellite-borne measurements of tropospheric nitrogen dioxide in the Po basin, J.Geophys. Res., 109, D15307, doi: 10.1029/2004JD004547.

• Petritoli A., E. Palazzi, C. Volta, G. Giovanelli, 2006, Validation of NO2 tropospheric column from space in the Po valley Italy, TROPOSAT-AT2 annual report 2005, Ed. Borrell Burrows, 308-312.

• Platt U., 1999, Modern methods of the measurements of atmospheric trace gases, Phys. Chem Chem Phys., 1, 5409-5415.

• Richter A., J. P. Burrows, 2002, Tropospheric NO2 from GOME measurements, Adv. Space Res., 29, 1673-1683

Many thanks for your attention