Effect of sea salt emissions on anthropogenic air pollution and nitrogen deposition in northwestern europe

Abstract

The North Sea region is characterised by several anthropogenic activities such as shipping, agriculture, industry and tourism. These activities go along with emissions of air pollutants such as NOX, NH3, and SO2 leading to the formation of HNO3, H2SO4, and particulate matter. Gaseous bases and acids (mainly HNO3, H2SO4 and NH3) tend to form new particles or to condense on existing ones. Meteorological conditions and size distribution of existing particles affect partitioning of these substances between gas and particle phase and between particle modes. In the marine troposphere, sea salt particles (mainly Cl–, Na+ and SO42-) account for a considerable amount of fine and coarse particles providing surface for condensation of above mentioned substances. The presence of sea salt may also affect N deposition because dry deposition velocities of gaseous substances and different particle modes vary considerably. In the presented study, the effect of sea salt emissions on atmospheric air pollution in the North Sea region was analysed by the means of the Community Multiscale Air Quality (CMAQ) Model. We simulated on a 24 × 24 km2 grid including the North and Baltic Sea. It was found, that the presence of sea salt increases coarse mode NH4+ and NO3- concentrations considerably while fine mode concentrations are decreased. This leads to increased total N deposition in coastal regions. At the same time, the deposition distant to the shore on the land as well as into the ocean decreases. However, this study shows that on spatial average only about 5 % of N deposition into the North Sea is caused by sea salt particles. Locally, the effect of sea salt on N deposition is partly higher. Therefore, sea salt emissions in regional air quality models are important for predicting the partitioning of anthropogenic pollutants between gas and particle phase and their deposition patterns correctly.