Factors influencing changes in rainwater composition from urban versus remote regions of the Yellow Sea

Rainwater samples were collected from three stations at the Yellow Sea in 1992-1993 and analyzed for some major species (Ca²⁺, K⁺, Na⁺, Mg²⁺, NO^3-, NH₄⁺, pH, PO₄^3-, and SO₄^2-). Absolute concentrations and element-to-sodium ratios show clear seasonal variations with higher levels in winter and lower levels in summer for most of the species. Levels of major species from urban areas can be twice as high as those of remote regions, in terms of both absolute concentration and element-to-sodium ratio. The contrasts between urban and remote and between low and high elevations can be explained by proximity to the ocean, local pollution sources, and scavenging processes. Comparison with other world areas shows rather high levels of chemical species in rainwater from the Yellow Sea relative to remote world oceans or even some other coastal urban areas. Using sodium as a sea-salt tracer, it was estimated that more than 50% of major species in rainwater could come from non-marine contributions, and for some species like NH₄⁺, NO₃^-, and SO₄^2-, anthropogenic emissions are definitely the major source. The high concentration of nitrogen species and elevated N/P ratio of rainwater, as compared to riverine input, suggest the significance of atmospheric wet deposition to the marine production and biogeochemical circulation of nutrients in this region.