Modelling intercontinental transport of atmospheric sulphur in the northern hemisphere

Intercontinental exchange of sulphur in major parts of the northern hemisphere has been studied with a 3-dimensional Eulerian transport model that resolves regional scale variability. Model results for 1988 have been evaluated against daily observations of sulphur dioxide and particulate sulphate in Europe and North America and show that the model reproduces the episodic character of oxidised sulphur in air. Yearly averages agree with the observations within a factor of 2, at over 75% of the sites. Monthly budgets for intercontinental exchange of sulphur are presented and related to large scale atmospheric flow patterns. Intercontinental transport of sulphur is related to mid-latitude cyclone tracks, and few events determine a considerable part of the yearly intercontinental exchange. European anthropogenic sulphur dominates the averaged air concentrations and depositions over the simulation area. The contribution of European sulphur over the Sea of Japan is calculated to be 50–75 mg(S) m^-2 yr^-1 or 5–10% of the total deposition calculated for that area. Over the West Siberian Planes, the European contribution is estimated to be 150–200 mg(S) m^-2 yr^-1 that is, 40–50% of the yearly calculated deposition. The relative contributions of intercontinental transport from anthropogenic sources in Asia and North America and biogenic sources in the North Atlantic Ocean to the European deposition levels are similar and range from 2 to 4%. In certain areas and seasons, however, these relative contributions can be much larger.