Abstract

Air pollution reduction measures in Europe have led to marked decreases in the levels of primary pollutants such as SO2 and NOx since the 1980s while for secondary pollutants like ozone and secondary inorganic aerosols (SIA) the effects of these measures are much less obvious. A recent extensive ... Show moreAir pollution reduction measures in Europe have led to marked decreases in the levels of primary pollutants such as SO2 and NOx since the 1980s while for secondary pollutants like ozone and secondary inorganic aerosols (SIA) the effects of these measures are much less obvious. A recent extensive comparison of the composition of particulate matter smaller than 10 μm (PM10) in Switzerland between the years 1998/1999 and 2008/2009, for example, revealed no changes in the levels of nitrates despite large NOx emission reductions over this period. Similarly, aerosol sulphates decreased much less strongly than the precursor gas SO2. In this study we used the online coupled regional chemistry-transport model COSMO-ART to investigate these non-linear responses of SIA components to changes in their precursor gases NOx, SO2 and NH3 focussing on wintertime conditions when PM concentrations are highest. We found that the reduced concentrations of NOx and NMVOC led to strong increases in the oxidation capacity of the European wintertime boundary layer as evidenced by pronounced enhancements in ozone, OH and N2O5 levels by sometimes more than 100 %. These changes resulted in accelerated formation of nitrates and sulphates and correspondingly smaller relative reductions in their concentrations as compared to the precursor gases, particularly within the densely populated and industrialized regions in Europe. Show less