Cluster analysis: A technique for estimating the synoptic meteorological controls on air and precipitation chemistry—Results from Eskdalemuir, South Scotland

Abstract

Abstract Clustering of isobaric trajectories arriving at Eskdalemuir, south Scotland, enabled us to isolate the influences of atmospheric transport patterns and precipitation amount on gas, aerosol and precipitation chemistry at this site. We conclude that at Eskdalemuir, 55% of the variation in summer season non-sea-salt sulphate concentration in rain may be explained by upwind history defined by trajectory clustering and by precipitation amount. Each cluster of trajectories could be described by distinct synoptic weather conditions, leading to the interesting prospect of assigning a typical ion concentration in precipitation to a given synoptic weather pattern. The scale of the synoptic patterns identified in this study were shown to be able to explain the variation in sulphur dioxide concentrations observed across a network of 50 stations contributing to the European Monitoring and Evaluation Programme. There is greater confidence in Global Climate Model simulations of future circulation patterns as a result of climate change than of equivalent simulations of temperature and precipitation distributions. A first approximation of future levels of ion deposition may therefore best be inferred from circulation pattern-ion concentration relationships of the type developed in this paper. The influence of other less certain changes in precipitation type/amount, scavenging processes and emission levels should then be assessed against a background of changes in the frequency of circulation patterns.