Deposition of sulphur and the acidity of precipitation over ireland

Abstract

Routine monthly measurements of airborne and precipitated sulphur over Ireland have been analysed, to determine the annual wet and dry deposition of sulphur, and compared with the predictions of a statistical long-range transport model. Comparisons between Ireland and south west Norway have been made, since in several ways the two regions are similar, being remote from major industrial sources in Europe. The difference in the sulphur concentration in rain is too small to account for the difference in the average acidity of rain in the two countries, and the importance of basic ions from non-industrial sources is noted. Rain over Ireland is only slightly acid and no trends in the acidity of rain have been found in data going back 15 years. It is not possible to estimate the effect on acidity of a reduction in sulphate. Comparisons are made between the measurements and calculations which indicate that only about 50 % of the measured deposition over Ireland can be explained by direct long-range transport from man-made sources. Of this 50 %, 65 % comes from sources in Great Britain. Errors in modelling are not sufficient to explain this difference and it is suggested that, in addition, in the Irish sampling network there may be sizeable local, natural and background contributions. A study of the correlation between measurements at adjacent sampling stations is consistent with the view that about 50% of the airborne sulphur over Ireland may come from distant sources.