1. Comparison between ground-based and satellite-derived measurements of NO 2 tropospheric column and ground concentration over the Po Valley in the frame of QUITSAT project S. Masieri 1, A. Petritoli 1, I. Kostadinov 1, F. Ravegnani 1, D. Bortoli 1,2, M. Premuda 1, W. Di Nicolantonio 3, C. Carnevale 4, E. Pisoni 4, M. Volta 4 and G.Giovanelli 1 A contribution to subproject ACCENT-TROPOSAT-2 (AT2), Task Group 3 1. ISAC-CNR, via Godetti,101, 40129 Bologna, Italy; 2. Geophysics Centre of Evora – University of Evora (CGE-UE), Portugal 3. Carlo Gavazzi Space at ISAC-CNR, via P. Gobetti 101, 40129, Bologna, Italy 4. Department of Electronics for Automation – University of Brescia, Italy

2. QUITSAT project overview Air Quality, obtained with algorithm definition of ground concentration parameters evaluated with the different analysis and integration activities in the frame of gas and PM monitoring:  P1 - Evaluation of surface concentration of PM derived by EO and non EO observation, model simulation and related maps  P2 – Monitoring of important events of desert and burning biomass aerosol, using imaging from geostationary satellites on board sensor  P3 – Ground concentration gas maps obtained with EO and non EO observation and model simulation  P4 – Estimation of VOC emission and CO column evaluation by satellite observation.  P5 – field of gas and PM concentration in synoptic scale on the QUITSAT domain.  Maps of Air Quality Index (AQI) on the interested areas Air QUality with Integration of ground-based and SAtellite measurement and Chemical Transport model

3. Activities description retrieving of NO 2 tropospheric VCD from satellite measurement (SCIAMACHY), using our satellite data processor retrieving of NO 2 tropospheric VCD by DOAS spectrometer at the ground level Integration of CTM and satellite observation to obtain ground level concentration of NO 2 Comparison between ARPA (Regional environmental agency) in-situ analyser network in satellite pixel and CTM grid, with comparison to active DOAS measurements

4. Satellite measurement of VCD of NO 2 1) The DOAS methodology furnish the total slant column density 2) The stratospheric contribution is removed by subtraction with a value obtained chosing a tropospheric 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]

5. AMF calculation Air Mass Factor was calculated applying the PROMSAR multiscattering model (Palazzi et al. 2005). It consist of a backword Montecarlo approach program and MODTRAN library used both for nadir (satellite) and Zenith (ground base DOAS spectrometer) measurement. The model has been run for different scenarios in witch also 4 level A.O.D., seasonal climatic parameters and rural or urban environment are considered.

6. The ARPA in-situ network Geographical location of the in situ ground-based sampling stations of the ARPA network in the Bologna area and the ISAC institute. ARPA, Regional environmental agency, with more than 100 stations in Po Valley, perform Air Quality

7. Scatter plot of all NO 2 ground-based measurements during QUITSAT field campaigns Differences are due to photochemical processes that have a different intensity. ARPA analyser is placed on centre of the City, the CNR area is in outskirt of Bologna (and far from urban sources). Considering only clear sky measurement the agreement coefficient goes from 0.678 to 0.7836 value of R 2

8. Integration of CTM and satellite observation Model used: GAMES [Volta et al., 2006], made by three modules: (a)the multi-phase Eulerian 3D photochemical model TCAM (Transport Chemical Aerosol Model, [Carnevale et al., 2008]; (b)the meteorological pre-processor PROMETEO; (c)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 cells, 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.

9. Model correction for satellite Ground Level concentration The merging between satellite values (SCIAMACHY in this case) and CTM simulations to get an improved ground level NO 2 concentration, is done according to the following steps: i) the NO 2 tropospheric column from satellite (C S ) and its error (  C S ) are estimated using DOAS technique; ii) similar quantities are obtained from the GAMES model (CM and  CM) by integrating the vertical profile to get the tropospheric columns (the model vertical extension is up to 4km). All the C M whose central latitude and longitude match the satellite ground pixel area are then averaged to get the final C M and  C M is its variance. iii) a corrected column (C C ) is thus calculated using C M and C S according to the following formula CC is a weighted average between C M and C S where the respective errors are the weights; iv) an average NO 2 profile corresponding to the satellite ground pixel is calculated from the model simulations and the respective column is scaled so to be equal to C C obtaining then a corrected profile. The Ground Level concentration, thus Corrected, is considered our final product (GLC NO2 ).

11. SCIAMACHY overpass on 2004, first comparison between in-situ analyser ARPA values vs ground values of CTM and vs corrected satellite value As we expect the all satellite pixel sottoexistimate the in-situ value so all point stay up the bisettrice line If we apply correction, we can see that comparison are better especially for blue point

12. Measuring NO 2 tropospheric VCD by DOAS spectrometer at the ground level Mt. Cimone Station (44.18 N, 10.70 E, 2165 m a.s.l.) Bologna Station (44.53 N, 11.30 E, 42 m a.s.l.) as urban area in the Po Valley S. Pietro Capofiume as rural area in the Po Valley East View of Po valley in which we can see the three station of measurements Schematic rappresentation of type of measurement performed Po valley is surrended by two montain ranges that can not facilitate recirculation of air masses

13. Conclusions and future applications Extension to all in-situ analyser present in QUITSAT domain is the next step in to satellite Air Quality validation. OMI data provided by TEMIS [http://www.temis.nl] in QUITSAT project will be utilized to improve our validation of ground concentration retrieved from satellite. New run of chemical transport model are available with data of 2008. DOAS TVC of NO2 (MT Cimone - Bologna)

14. 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 (Tropospheric Emission Monitoring Internet Service) [http://www.temis.nl] to providing OMI level 2 data of NO 2 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 e di 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

15. 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