Aerosols have in recent years been given increased attention due to their effects on climate and health. Drastic reductions in sulphur emissions in Europe during the last two decades have led to a larger relative importance of nitrate aerosols. However, large uncertainties still exist in the representation of nitrate in atmospheric models.
In this thesis heterogeneous reactions of HNO3 on dust and sea-salt, representing a major pathway of nitrate formation, have been implemented in the Unified EMEP model. A kinetic approach has been used assuming a total reaction in the direction towards nitrate. The aim of this thesis has been to investigate whether reactions of HNO3 on dust and sea-salt can improve the Unified EMEP model's performance in terms of nitrate compounds. A stepwise approach has been chosen to implement the different processes and reaction sites one after another.
In June 2006 and January 2007 two intensive measurement campaigns where conducted, which separated coarse and fine nitrate. In this thesis, the results of the new nitrate implementation have been evaluated in detail against these and other measurements within the EMEP network, showing that the temporal correlation of coarse nitrate has clearly improved. However, it has also been found that the implementation yields too small values of coarse nitrate over land. This negative bias will be an important issue for future work.