Chemical characteristics of PM2.5 during haze episodes in the urban of Fuzhou, China

Abstract

Atmospheric fine particles (PM2.5) were collected in this study with middle volume samplers in Fuzhou, China, during both normal days and haze days in summer (September 2007) and winter (January 2008). The concentrations, distributions, and sources of polycyclic aromatic hydrocarbons (PAHs), organic carbon (OC), elemental carbon (EC), and water soluble inorganic ions (WSIIs) were determinated. The results showed that the concentrations of PM2.5, PAHs, OC, EC, and WSIIs were in the orders of haze>normal and winter>summer. The dominant PAHs of PM2.5 in Fuzhou were Fluo, Pyr, Chr, BbF, BkF, BaP, BghiP, and IcdP, which represented about 80.0% of the total PAHs during different sampling periods. The BaPeq concentrations of ∑PAHs were 0.78, 0.99, 1.22, and 2.43ng/m3 in summer normal, summer haze, winter normal, and winter haze, respectively. Secondary pollutants (SO42−, NO3−, NH4+, and OC) were the major chemical compositions of PM2.5, accounting for 69.0%, 55.1%, 63.4%, and 64.9% of PM2.5 mass in summer normal, summer haze, winter normal, and winter haze, respectively. Correspondingly, secondary organic carbon (SOC) in Fuzhou accounted for 20.1%, 48.6%, 24.5%, and 50.5% of OC. The average values of nitrogen oxidation ratio (NOR) and sulfur oxidation ratio (SOR) were higher in haze days (0.08 and 0.27) than in normal days (0.05 and 0.22). Higher OC/EC ratios were also found in haze days (5.0) than in normal days (3.3). Correlation analysis demonstrated that visibility had positive correlations with wind speed, and negative correlations with relative humidity and major air pollutants. Overall, the enrichments of PM2.5, OC, EC, SO42−, and NO3− promoted haze formation. Furthermore, the diagnostic ratios of IcdP/(IcdP+BghiP), IcdP/BghiP, OC/EC, and NO3−/SO42− indicated that vehicle exhaust and coal consumption were the main sources of pollutants in Fuzhou.