Air masses and weather types: a useful tool for characterizing precipitation chemistry and wet deposition

This study is an analysis of 344 days with rainfall recorded during five years in a remote regional background EMEP (Cooperative Programme for the Monitoring and Evaluation of the Long Range Transmission of Air Pollutants in Europe) station in Spain. The chemical composition of the rainwater associated with air masses (nine categories) and weather types (26 categories) was characterized. The chemical composition of rainwater was dominated by calcium (Ca2+) and sulphate (SO42−-S), with VWM (Volume Weighted Mean) during the period studied (2002–2006), with 55 μeq/L and 34 μeqS/L, respectively. Calcium, sodium (Na+), ammonium (NH4+-N) and magnesium (Mg2+) seem to be dominant components in the neutralization of the rainwater. By applying Pearson correlations, principal component analysis and enrichment factors, it is possible to identify source types for the precipitation constituents. Interannual and intra-annual variability was also been studied. High calcium levels are associated with the frequent intrusions of Saharan dust that occur during the summer, and the maximums of chlorine and sodium in the winter may be due to the greater amount of maritime air recorded during this season. Wet deposition was determined by focusing on nitrogen deposition, registering mean annual values of 155 mgN/m2/year (from the NO3−-N) and 165 mgN/m2/year (from the NH4+-N).The authors would like to thank Alberto Gonzalez Ortíz (Ministry of the Environment, Spain) and Andrés Alastuey (Jaume Almera Institut, CSIC, Spain) for the information provided about the EMEP station at Víznar. We would also like to thank Borja Ruíz Reverter for the classification of the back-trajectories. The authors are also in debt to Antonio M. Ortín for the graphic design. The authors gratefully acknowledge the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and dispersion model and/or READY website (http://ready.arl.noaa.gov) used in this publication. This study has been supported by the Spanish Ministry of Education (Projects CGL2007-66477-C02-01, TEC200763216), the Spanish Ministry of Science and Technology (Projects CGL2010-18782 and CSD2007–00067), the Andalusian Regional Government (Projects P06-RNM- 01503, P08-RNM-3568, and P10-RNM-6299), the European Union through ACTRIS project (EU INFRA-2010-1.1.16– 262254) and by the Castile and Leon Regional Government (Project LE039A10-2).publishe