The control by atmospheric pressure patterns of sulphate concentrations in precipitation at Eskdalemuir, Scotland

It is shown that, on a monthly basis, certain sea-level atmospheric pressure patterns can be identified which are conducive to, or mitigate against, high excess sulphate concentrations in precipitation at Eskdalemuir, Scotland. This is not simply a consequence of the amount of precipitation influencing the concentration. The differences in the pressure patterns for months grouped into 'high' and 'low' excess sulphate concentration reflect the relative importance of transport from pollutant source regions and from regions with relatively small source strengths. It is the intensity of the pressure gradients over Europe and the Atlantic, combined with the position of the meridional axis of the Iceland Low/Azores High couplet, which appears to influence the monthly excess sulphate concentration in precipitation. The existence of these relationships on a monthly time-scale points towards a climatic control on acidic deposition, and introduces the possible role of climatic change.