Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 6 2 2006 10.5194/acp-6-329-2006 http://www.atmos-chem-phys.net/6/329/2006/ http://www.atmos-chem-phys.net/6/329/2006/acp-6-329-2006.html http://www.atmos-chem-phys.net/6/329/2006/acp-6-329-2006.pdf 329 338 2006-02-06 Airborne multi-axis DOAS measurements of tropospheric SO₂ plumes in the Po-valley, Italy P. Wang A. Richter M. Bruns J. P. Burrows R. Scheele W. Junkermann K.-P. Heue T. Wagner U. Platt I. Pundt Institute of Environmental Physics, University of Bremen, Germany Royal Netherlands Meteorological Institute (KNMI), De Bilt, the Netherlands Research Center Karlsruhe, IMK-IFU, Garmisch-Partenkirchen, Germany Institute of Environmental Physics, University of Heidelberg, Germany During the second FORMAT (FORMaldehyde as A Tracer of oxidation in the troposphere) campaign in 2003 the airborne multi-axis DOAS instrument (AMAXDOAS) performed scattered-light spectroscopic measurements of SO₂ over the city of Mantova and the power plant Porto Tolle, both situated in the Po-valley, Northern Italy. The SO₂ vertical columns and emission flux were derived from two days of measurements, 26 and 27 September 2003. The SO₂ emission flux from the power plant Porto Tolle was calculated to 1.93×10²⁵ molec s^-1 on 26 September and in good agreement with official emission data, which quote 2.25×10²⁵ molec s^-1. On 27 September the measured flux was much lower (3.77×10²⁴ molec s^-1) if ECMWF wind data are used, but of comparable magnitude (2.4×10²⁵ molec s^-1) if the aircraft on-board wind measurements are utilised. Official emission data was 2.07×10²⁵ molec s^-1 indicating only a small change from the previous day. Over the city of Mantova, the observed SO₂ vertical columns were 1.1×10¹⁶ molec cm^-2 and 1.9×10¹⁶ molec cm^-2 on 26 and 27 September, respectively. This is in good agreement with ground-based measurements of 5.9 ppbv and 10.0 ppbv which correspond to 1.2×10¹⁶ molec cm^-2 and 2.2×10¹⁶ molec cm^-2 if a well mixed boundary layer of 500m altitude is assumed.