The ion chemistry, seasonal cycle, and sources of PM2.5 and TSP aerosol in Shanghai

Daily total suspended particulate (TSP), particle size smaller than 100 mu m and particle size smaller than 2.5 mu m (PM2.5) aerosol samples were collected at two sites in Shanghai in four seasons from September 2003 to January 2005. Concentrations of the water-soluble ions (SO42-, NO3-, Cl-, F-, PO43-, HCOO-, CH3COO-, NO2-, MSA, C2O42-, NH4+, Ca2+, Na+, K+ Mg2+) were measured for a total of 202 samples. Daily TSP and PM2.5 mass concentrations ranged from 66.1 to 666.8 mu g m(-3) and 17.8 to 217.9 mu g m(-3), with annual average concentrations of 230.5 and 94.6 mu g m-3, respectively. The sum of ions contributed an average of 26% and 32% of TSP and PM2.5 mass concentrations, respectively. In PM2.5, the concentration of the major ions followed the order of SO42- > NO3- > NH4+ > Cl- > Ca2+ > K+. while in TSP was SO42- > NO3- > Cl- > Ca2+ > NH4+ > Na+. These major ions were mainly in the form of (NH4)(2)SO4, Ca(NO3)(2), CaCl2, and CaSO4 in aerosol particles. The aerosol was slightly acidic in the fine particle size range, and alkaline in the coarse mode. Seasonal variation of ion concentrations was significant, with the highest concentrations observed in winter and spring and the lowest in summer and autumn. Three types of air masses, i.e. marine, mixing, and continental, were frequently observed, and their distribution in four seasons might result in the clear seasonal variation. It is Shanghai that has the highest NO3-/SO42- value among all of those cities in China, indicating that as the biggest city in China the mobile source of the air pollution becomes more and more predominant. However, stationary emissions were still the dominant source in Shanghai indicated by the NO3-/SO42- ratio of lower than 1. The formation of NO3- was largely from the gas-phase photochemical reaction in the cold season, and from the heterogeneous reaction in the warm season, while the formation of SO42- might be from the heterogeneous reaction in the entire year round. NH4+, K+, Cl-, NO3-, and SO42- were mainly influenced by the anthropogenic emissions in land, meanwhile Cl- and SO42- might be partly influenced by the sea. Na+, Mg2+, and Ca2+ were derived from both inland crustal and marine sources. Chloride depletion was found especially in summer. The air pollution in Shanghai has proved to be under the influence of both the local emissions and the long-range transport from outside areas. (c) 2006 Published by Elsevier Ltd.