Secondary inorganic aerosol simulations for Europe with special attention to nitrate

[摘要] Nitrate is an important component of (secondary inorganic) fine aerosols in Europe. We presenta model simulation for the year 1995 in which we account for the formation of secondary inorganicaerosols including ammonium sulphate and ammonium nitrate, a semi volatile component. For thispurpose, the chemistry-transport model LOTOS was extended with a thermodynamic equilibrium moduleand additional relevant processes to account for secondary aerosol formation and deposition. Duringwinter, fall and especially spring high nitrate levels are projected over north western, centraland eastern Europe. During winter nitrate concentrations are highest in Italy, in accordance withobserved data. In winter nitric acid, the precursor for aerosol nitrate is formed throughheterogeneous reactions on the surface of aerosols. Modelled and observed sulphate concentrationsshow little seasonal variation. Compared to sulphate levels, appreciable ammonium nitrate concentrationsin summer are limited to those areas with high ammonia emissions, e.g. the Netherlands, since highammonia concentrations are necessary to stabilise this aerosol component at high temperatures. Asa consequence of the strong seasonal variation in nitrate levels the AOD depth of nitrate overEurope is especially significant compared to that of sulphate in winter and spring when equalAOD values are calculated over large parts of Europe. Averaged over all stations the modelreproduces the measured concentrations for NO₃, SO₄, NH₄, TNO₃ (HNO₃+NO₃),TNH₄ (NH₃+NH₄) and SO₂within 20%. The daily variation is captured well, albeit that the model does not always representthe amplitude of single events. The model underestimates wet deposition which was attributed to thecrude representation of cloud processes. Comparison of retrieved and computed aerosol optical depth (AOD)showed that the model underestimates AOD significantly, which was expected due to the lack ofcarbonaceous aerosols, sea salt and dust in the model. The treatment of ammonia was found tobe a major source for uncertainties in the model representation of secondary aerosols. Also,inclusion of sea salt is necessary to properly assess the nitrate and nitric acid levels in marine areas.

[学科分类] 大气科学