DEPOSITION OF ATMOSPHERIC POLLUTANTS TO THE LOIS AREA

UK national deposition models were used to estimate deposition of a ra nge of pollutant compounds to the river catchments in eastern Britain as part of the LOIS programme. Nitrogen dioxide and ammonia concentrat ions in air were monitored for two catchments, the Tweed and the Ouse. The nitrogen dioxide concentrations in the Ouse were lower than expec ted from the UK concentration maps, but the ammonia concentrations sup ported the UK mapped values in both catchments. The uncertainties in t he deposition estimates are discussed and the estimates are compared w ith other available data. The uncertainty in estimated deposition of o xidised nitrogen was of concern. Comparison with river chemical load d ata suggested that modelled atmospheric inputs accounted for 20% of th e sulphate river load and probably less than 30% of the chloride river load. In the Humber area there was evidence of substantial, but unqua ntified, deposition of hydrogen chloride gas. It appears that the atmo sphere is not a major source of calcium, magnesium or the heavy metals . The complexity of vegetation and soil processes with nitrogen compou nds makes interpretation difficult. The results, however, suggest a su bstantial non-atmospheric input of sulphate and chloride in all catchm ents in the LOIS area. (C) 1997 Elsevier Science B.V.