Long-term modelling of airborne pollution within the Northern Hemisphere

A long-term modelling (1991–1994) of oxidised sulphur, bound nitrogen and some heavy metals has been carried out by MSC-E/EMEP for the Northern Hemisphere. The transport unit of the model is an Eulerian scheme which could be classified as Pseudo-Lagrangian one. Vertical distribution described by means of Gaussian approximation and the exchange with the free troposphere are taken into account. Vertical movement is calculated proceeding from local mixing conditions, state of the surface, its height (topography) etc. The chemical unit for acid compounds contains 25 reactions and 14 compounds including sulphur and nitrogen compounds peroxyacetylnitrate, tropospheric ozone, volatile hydrocarbons (but methane) are considered as a whole via ozone creation potential. The model time step is 1 hour, meteorological data (winds, temperature, precipitation etc.) cover 6-hour intervals. The model results show that very significant part of the Arctic and West Asian acid pollution is produced by European countries. On the whole the Arctic pollution by SO_x, NO_x and NH_x comes from sources of Old World. The main source of sulphur pollution is located in Russia and of nitrogen compound — in Central and Northern Europe. About 50% SO_x, 70% NO_x and 40% NH_x deposition in Central Asia and Kazakhstan is-imported from external sources. A similar situation is observed in European and Asian parts of Russia.