Assessment of the use of principal components analysis to relate air precipitation chemistry to climate

A classification of atmospheric circulation was derived using principal components analysis (PCA) of daily sea level pressure over a 10 year period. Correlation coefficients of up to 0.65 were obtained between the individual principal component loadings and monthly means of gas and precipitation ion concentrations for a Scottish and a Norwegian station from the European Monitoring and Evaluation Programme (EMEP) network. The mean synoptic patterns of months predicted to have high or low gas and ion concentrations from their component loadings agreed well with previous work. High concentrations occur frequently with southerly flow or anticyclonic conditions, and low concentrations with westerly and northwesterly flow. We conclude that the PCA classification is a sensible method to use to derive circulation pattern-pollutant relationships, and is an encouraging first step to use the general circulation model (GCM) projections of future climate to assess possible future air/precipitation composition patterns.