Atmospheric deposition of mercury in central Poland: Sources and seasonal trends

• The first study of atmospheric mercury in precipitation over central Poland.
• Hg concentrations were much higher at the urban site compared to the forest site.
• Seasonal variation in rainwater Hg concentrations depends on anthropogenic emission and meteorological conditions.
• The contribution of local/regional and long-range transport from polluted areas in Europe was substantial.

Atmospheric deposition of total mercury was studied at two sites in central Poland, between April 2013 and October 2014. Hg in rainwater (bulk deposition) was analyzed in relation to meteorological parameters and major ions (H+, NO3−, Cl−, SO42 −) in order to investigate seasonal variation, identify sources and determine factors affecting atmospheric Hg chemistry and deposition. Total mercury concentrations varied between 1.24 and 22.1 ng L− 1 at the urban sampling site (Poznań) and between 0.57 and 18.3 ng L− 1 in the woodland protected area (Jeziory), with quite similar mean values of 6.96 and 6.37 ng L− 1, respectively. Mercury in precipitation exhibited lower spatial variability within the study domain (urban/forest transect) than the concentrations determined during other similar observations, reflecting the predominant influence of the same local sources. In our study, a significant seasonal pattern of Hg deposition was observed at both sampling sites, with higher and more variable concentrations of Hg reported for the urban area. In particular, deposition values of Hg were higher in the samples attributed to relatively large precipitation amounts in the summer and in those collected during the winter season (the result of higher contributions from combustion sources, i.e. intensive combustion of fossil fuels in residential and commercial boilers, individual power/heat-generating plants). In addition, a significant relationship between Hg concentration and precipitation amount was found while considering different types of wintertime samples (i.e. rain, snow and mixed precipitation). The analysis of backward trajectories showed that air masses arriving from polluted regions of western Europe and southern Poland largely affected the amount of Hg in rainwater. A seasonal variation in Hg deposition fluxes was also observed, with the maximum value of Hg in spring and minimum in winter. Our results indicated that rainwater Hg and, consequently, the wet deposition flux of Hg are related to seasonal differences in precipitation (type, intensity, amount) and the emission source.