A study of the source–receptor relationships influencing the acidity of precipitation collected at a rural site in France

In order to examine the qualitative and quantitative source–receptor relationships responsible for acid rains at a background site in France, a receptor-oriented model was applied to the precipitation data collected from 1992 to 1995. Origins of acidic and alkaline species in precipitations have been investigated. The methodology combines precipitation chemical data with air parcel backward trajectories to establish concentration field maps of likely contributing sources. Highest acidities and concentrations of sulfate and nitrate in precipitation were associated with transport from the high emission areas of central Europe. Alkaline events were associated with air masses originating from Mediterranean basin or northern Africa. The quantitative relationships between the maps of potential sources and the European emissions of SO2 and NOx were examined performing a correlation analysis. Good correlations were found between computed concentrations of acidic species and emissions of SO2 and NOx. Substantial seasonal variations of acidic species were revealed. The highest concentrations occurred during the warm season. These seasonal variations are the effect of change of meteorological conditions and of the strength atmospheric processes according to the season.