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 influence on the transport and ultimate deposition of atmospheric pollutants. One potential outcome of climate change is alteration of atmospheric circulation patterns. The first stage in the development of a downscaling methodology to assess the influence of these possible future atmospheric circulation changes on transport and deposition of atmospheric pollutants over Europe is described. Firstly, the main modes of regional-scale circulation over a domain covering the North Atlantic and Europe are determined using principal components analysis of sea level pressure patterns. To determine whether the principal components represent circulation types found in reality, and show realistic relationships with surface temperature and precipitation amount, they are compared to the Lamb Weather Types, Central Eng land Temperature, and England and Wales Rainfall. There are statistically significant relationships between some of the principal components and aqueous and ambient pollutant concentrations at 5 selected stations from the European Monitoring and Evaluation Programme monitoring network. Although, for any one combination of principal component and pollutant variable, the level of explanation can be quite small, notwithstanding some levels of variance explained for individual combinations being up to 69 % (45 % for the winter season, described in detail here). Because the pollution climate at any one location is a function of many combinations of circulation/pollution relationships, despite the relatively small magnitude of variance explained for individual combinations in this study. the results confirm the utility of atmospheric circulation principal components in deriving downscaling relationships for surface pollution behaviour (via eventual multiple regressions, not reported in this paper), as well as giving further insight into the climatic influences on air and precipitation chemistry over Europe.