Abstract
Spatial and temporal variability of carbon species in rainwater (bulk deposition) was studied for the first time at two sites located in urban area of Poznań City and protected woodland area (Jeziory), in central Poland, between April and December 2013. The mean concentration of total carbon (TC) for the first site was 5.86 mg L−1, whereas for the second, 5.21 mg L−1. Dissolved organic carbon (DOC) concentration accounted for, on average, 87 and 91 % of total carbon in precipitation at urban and non-urban sites, respectively. Significant changes in TC concentrations in rainwater were observed at both sites, indicating that atmospheric transformation, transport, and removal mechanisms of carbonaceous particles were affected by seasonal fluctuations in biogenic/anthropogenic emission and meteorological conditions (i.e., precipitation height and type, atmospheric transport). During the warm season, the DOC concentration in rainwater was mostly influenced by mixed natural and anthropogenic sources. In contrast, during the cold season, the DOC concentration significantly increased mainly as a result of anthropogenic activities, i.e., intensive coal combustion, domestic wood burning, high-temperature processes, etc. In addition, during the winter measurements, significant differences in mean DOC concentration (Kruskal-Wallis test, p < 0.05) were determined for rain, mixed rain-snow, and snow samples. It was found that rainwater TOC concentration measured in Poznań and Jeziory reflected a combination of local, regional, and distant sources. Backward trajectory analysis showed that air masses advected from polluted regions in western Europe largely affect the DOC amount in rainwater, both at urban and non-urban sites. These data imply that carbonaceous compounds are of crucial importance in atmospheric chemistry and should be considered as an important parameter while considering wet deposition, reactions with different substances, especially over polluted environments.
Highlights
Light-absorbing carbon aggregates in the atmosphere affect cloud formation and photochemical transformations (Ramanathan and Carmichael 2008)
Dissolved organic carbon (DOC) concentrations in rainwater gradually increased to the level >12 mg L−1 over the whole harvest/dry period, with one rain episode characterized by extremely high level of DOC (204 mg L−1)
Concentrations of dissolved organic carbon, total carbon, and inorganic carbon were simultaneously determined in rainwater samples in the period between April and December 2013 at urban and forest sites in central Poland
Summary
Light-absorbing carbon aggregates in the atmosphere affect cloud formation and photochemical transformations (Ramanathan and Carmichael 2008). Atmospheric organic carbon exists mainly in gaseous and aerosol phase and can be associated with both anthropogenic (urban/industrial emission) and biogenic (vegetation, large-scale biomass burning of forests, sugar cane foliage and bagasse) sources. It was calculated that annual global rainwater dissolved organic carbon (DOC) flux may equal 0.43 Gt C year−1; over urban environments, the concentration and deposition fluxes of organic carbon are most often elevated as compared to rural areas (Willey et al 2000). Other sources of atmospheric carbon such as petrochemical industry (fertilizers, catalyst regeneration facilities), traffic (road dust and vehicle emission), and smelters are typical of urban areas. Despite previous observations focused on the characteristics of carbonaceous aerosol, there are still not enough data on DOC measurements in rainwater from the central and eastern Europe
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