Abstract
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).
Highlights
Rain acts as a powerful mechanism to remove pollutants from the atmosphere
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
To better characterize dominant meteorological influences and airmasses pathways, the database of rainwater chemical composition has been analysed through both classifications; Fig. 4 and Fig. 5 provide these clustered values of the VWM
Summary
Rain acts as a powerful mechanism to remove pollutants from the atmosphere. Precipitation chemistry is the result of a series of in-cloud and below-cloud atmospheric chemical reactions and a complex interaction between microphysical processes and cloud dynamics (Mouli et al, 2005). The importance of studing chemical composition of rainwater focus on several aspects: i) it is a valuable tool that helps us to identify the pollutant sources involved in this composition; ii) it provides information on the transportation and dispersion of pollution; iii) it is involved in problems related to acid deposition, eutrophication, trace metal deposition, biogeochemical cycling, ecosystem health and global climate change and iv) it is a very useful tool for validating model. Aerosols and gases released into the atmosphere can be transported over long distance from their source, and can be removed by dry or wet deposition Background levels, established for remote areas far from the direct impact of anthropogenic sources, provide relevant information mainly because it allows us to determine the extent of anthropogenic pollution as well as to address the potential influence of long-range transport to rural areas. Networks of wet deposition are very useful to establish appropriate thresholds (Das et al, 2010a) for policy decisions.
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