Chemical composition of summertime aerosol in the Po Valley (Italy), northern Adriatic and Black Sea

Abstract

The Aerosol Direct Radiative Impact Experiment was conducted over the Po Valley, the northern Adriatic and the Black Sea in summer 2004, with the aim of characterizing physical, chemical and optical properties of the ambient aerosols, and calculating its direct impact on the radiative balance of the region. The UK BAE-146 FAAM aircraft sampled in situ, while surface lidar and AERONET measurements were also taken. Ammonium sulphate and organics were found to dominate sub-micron aerosol composition when air-mass trajectories showed easterly flow. Under westerly anticyclonic flow, venting and recirculation of Po Valley surface air resulted in vertical stratification over both the Po Valley and northern Adriatic. Large ammonium nitrate concentrations were found in this recirculating air due to the large NOx and ammonium sources in the Po Valley. This large amount of ammonium nitrate makes a significant contribution to the regional radiative budget. Not only is it the most significant component mass in the column when Po Valley air flows over the Adriatic Sea, but the scattering will increase substantially due to additional amounts of water on aerosol particles rich in ammonium nitrate which are found in moist air masses. Organic aerosol mass was dominated by secondary material in both easterly and westerly conditions, with a relative reduction in the number of di- and poly-acidic functional groups in the nitrate-rich westerly air masses. Black Sea aerosol composition was dominated by ammonium sulphate and organic aerosol. Copyright © 2007 Royal Meteorological Society.