Modelling PM 2.5 concentrations over Europe: the role of agriculture

Abstract

Emissions from agricultural activities influence the concentration of fine particulate matter on a European scale. Ammonia plays a key role in the formation of secondary inorganic PM by neutralising acid gases. In this paper the LOTOS model is described, which has been used to simulate the fine inorganic particulate mass over Europe. In addition, concentrations fields due to primary emitted particles were calculated. Sulphate was neutralised by ammonia over the whole domain. Excess ammonia is then available for the formation of ammonium nitrate, which was found to be present in similar amounts as sulphate during winter. In summer nitrate seems to be limited to north western Europe and the Po valley in Italy. The model is able to reproduce spatial and seasonal features as have been observed in reality. Agreement between model and measurements are favourable at continental sites in north western and central Europe. However, in coastal regions nitrate concentrations are underestimated. During winter the formation of ammonium nitrate appears to be sensitive to the availability of nitrate. The sensitivity to ammonia seems to be less, when only the partitioning of nitrate between the particulate and the gaseous phase is studied. However, changing the ammonia emission by 25 % shows a non-linear response with 10 - 50 % change in the nitrate concentration over large areas in Europe. Primary emissions of fine particles due to agricultural activities do not contribute a large fraction to PM levels in Europe.