Impact of mixed anthropogenic and natural emissions on air quality and eco-environment—the major water-soluble components in aerosols from northwest to offshore isle

Abstract

Based on more than 300 atmospheric TSP and PM2.5 samples collected at five sites over China in 2007 and 2008, characteristics, sources, and interactions of the major water-soluble species were investigated for a better understanding of their role in urban air quality and offshore eco-environment. From the dust source regions in Northwestern China to an offshore isle over the East China Sea, concentration levels and fine/coarse particle distributions of five representative water-soluble components were well elucidated, reflecting the distinct differences of geo-history, location, and present economic situation among the target areas. NO3−/SO42− mass ratios reflected significant divergence of motorization among the studied regions. Specifically, a case study during the World Car-Free Day proved that traffic restriction measures could indeed help mitigate the aerosol species formed from vehicle emissions. Investigation on the molar concentration stoichiometry and mass percentage variations of particulate NO3−, SO42−, and NH4+ revealed that NH3 was a driving factor in the formation of major secondary water-soluble ions in atmospheric fine particles over urban areas. Based on the prevailing wind analysis, observation over an offshore isle clearly indicated the influence of the relative strength of anthropogenic sources and ocean-related natural sources on the formation and size distribution of MSA (methanesulfonic acid), a major water-soluble organic component in aerosol. Annual dry deposition flux of particulate NO3− and NH4+ over the East China Sea was estimated based on the strength of an improved calculation formula. Reductive nitrogen was found to be the major form of the deposited atmospheric inorganic nitrogen, accounting for ~ 69% of the total nitrogen depositions.