Comparison on aerosol physicochemical properties of sea and land along the coast of Bohai, China

Abstract

The Bohai Sea is one of four major sea areas adjacent to China, air pollution is becoming an issue along the Bohai coast owing to rapid industrialization and urbanization. To analyze the sea–land interaction and its influence on regional particulate pollution, a comparison of sea and land aerosol physicochemical properties was carried out using observations and numerical simulation. Three observation sites, an ocean site on the Bohai Sea, a coastal station in the Tanggu district, and an inland station in Tianjin City were established. The movements and interactions of pollutants between land and sea were determined, and it was found that the convergence of sea–land breezes produced an ascending motion, which served to concentrate pollutants, with the polluted central body of air extending upward to a height of 200 m. The proportion of fine particle aerosols was greater in Bohai than at the inland site, although aerosol pollution levels over land were higher than those over ocean. The annual average aerosol optical depths, at the Bohai and inland sites were 0.74 and 0.82, and the annual average wavelength indices were 0.97 and 0.90, respectively. The spatial distribution of PM2.5 concentration was characterized as inland > Bohai > coastal zone, which reflected local emissions, the special terrain and meteorological conditions of the coastal zone. Higher concentrations of EC, SO42−, Mg, Al, V, and Cr at Bohai, compared to the other sites, might have been due to ship emissions on the Bohai Sea, while industrial development could explain why the maximum concentrations of Fe and NO3− were observed at the coastal site. In addition, the diurnal distribution of SO42− exhibited a trend opposite to that for humidity, both at the Bohai and coastal sites, which indicated that, in addition to secondary transformation under high humidity conditions, sulfate emission sources were located locally.