Trace elements and major ions in atmospheric wet and dry deposition across central Illinois, USA

Abstract

Measurements of trace elements and major ions in wet and dry deposition were made at eight sites in central Illinois for a 1-month period during the spring/summer season in 2011. During this study, daily-event wet deposition was collected using a commonly utilized sampling train, while 72-h dry deposition collection employed a newly developed artificial turf surrogate surface sampler designed to be more representative of natural deposition surfaces. Results showed considerable intersite variability in the amounts of wet and dry deposition received at sites. Wet deposition loadings of Hg, Pb, S, and As were higher at more southerly network sites due to higher precipitation depths and proximity to sources in the electricity generating and iron and steel manufacturing sectors. Dry deposition loadings of Hg, Pb, S, Cu, Zn, and As were higher at northerly sites, and one urban site had the highest loadings of Pb, S, Cu, and Zn consistent with its proximity (3 km) to very large sources in the electricity generating and iron and steel manufacturing sectors. Enrichment factor analysis showed moderate to high enrichment in both wet and dry deposition samples, suggesting that anthropogenic sources contributed to deposition of many trace elements measured during this study. Analysis of trace element ratios in wet and dry deposition for anthropogenically derived elements provided insight into sources impacting the study sites. Arsenic-sulfur, selenium-sulfur, and mercury-sulfate interrelationships in wet deposition suggested that regional coal combustion sources were impacting receptor sites, while relationships were less pronounced in dry deposition samples suggesting less influence from regional coal combustion sources. In addition to measurements indicating the importance of near field contributions to dry deposition, this study overall demonstrated successful application of a novel method for the direct measurement of trace elements and major ions in the dry component of atmospheric deposition, which may be considered for future studies in other similar emission source regions.