Seasonal variations and chemical compositions of PM2.5 aerosol in the urban area of Fuzhou, China

The mass concentrations and chemical compositions (elements, water-soluble ions and carbonaceous species) of PM2.5 aerosol were detected in the urban area of Fuzhou city across four seasons from April 2007 to January 2008. The mass concentrations of PM2.5 ranged from 18.45 to 78.89μg/m3, with the average value of 44.33±16.30μg/m3. The elemental compositions were dominated by Si, Ca, Fe, K, and Al. SO42−, NO3−, and NH4+ were the major ions, contributing 24.3%, 9.9%, and 8.8% to the total PM2.5 mass. The concentrations of above ions showed distinct seasonality of 2.2, 8.0, and 5.9 times higher in winter than those in summer, respectively. (NH4)2SO4 and NH4NO3 were the main forms in summer and winter and NH4NO3 mainly existed in autumn, while (NH4)2SO4, NH4HSO4 and NH4NO3 existed in spring. The high NO3−/SO42− ratio suggested that vehicular exhaust made an important contribution to atmospheric pollution. TC occupied 24.1% of PM2.5 mass, with a distribution of 19.2% OC and 4.9% EC. OC and EC had the common dominant sources in spring due to their strong correlation. The OC/EC ratio showed obviously seasonal distribution of 5.0 in spring, 2.7 in summer, 3.6 in autumn, and 4.2 in winter. The material balance analysis indicated that the fractions of major chemical species in PM2.5 were in the following order: OM>sulfate>soil dust>nitrate>ammonium>EC>chloride. ► Acidic ions (SO42−, and NO3−) in PM2.5 were neutralized mainly by NH4+. ► The speciation of major ions was inferred in different seasons. ► Vehicular exhaust was an important pollution source in addition to coal combustion.