The influence of climate on air and precipitation chemistry over Europe and downscaling applications to future acidic deposition

Atmospheric circulations, and related climate conditions, exert a strong in fluence on the transport and ultimate deposition of atmospheric pollutants. One potential outcome of climate change is alteration of atmospheric circu lation patterns. The first stage in the development of a downscaling method ology to assess the influence of these possible future atmospheric circulat ion changes on transport and deposition of atmospheric pollutants over Euro pe is described. Firstly, the main modes of regional-scale circulation over a domain covering the North Atlantic and Europe are determined using princ ipal components analysis of sea level pressure patterns. To determine wheth er the principal components represent circulation types found in reality, a nd show realistic relationships with surface temperature and precipitation amount, they are compared to the Lamb Weather Types, Central Eng land Tempe rature, and England and Wales Rainfall. There are statistically significant relationships between some of the principal components and aqueous and amb ient pollutant concentrations at 5 selected stations from the European Moni toring and Evaluation Programme monitoring network. Although, for any one c ombination of principal component and pollutant variable, the level of expl anation can be quite small, notwithstanding some levels of variance explain ed for individual combinations being up to 69 % (45 % for the winter season , described in detail here). Because the pollution climate at any one locat ion is a function of many combinations of circulation/pollution relationshi ps, despite the relatively small magnitude of variance explained for indivi dual combinations in this study. the results confirm the utility of atmosph eric circulation principal components in deriving downscaling relationships for surface pollution behaviour (via eventual multiple regressions, not re ported in this paper), as well as giving further insight into the climatic influences on air and precipitation chemistry over Europe.