Seasonal variations and chemical characteristics of PM_(2.5) in Wuhan, central China

摘要

PM_(2.5) samples were collected at an urban site (WD) and a suburban site (TH) in Wuhan from August 2012 to July 2013. The mass concentrations of water-soluble inorganic ions, carbonaceous species and elements of PM_(2.5) were measured. The annual mean concentrations of PM_(2.5) were 106.5 μg/m~3 and 114.9 μg/m~3 at WD and TH, respectively. The chemical compositions of PM_(2.5) at WD were similar to those at TH and the fractions of the major components of PM_(2.5) in Wuhan were in the following order of trace elements ＜ chloride ＜ EC (elemental carbon) ＜ ammonium ＜ nitrate ＜ soil dust ＜ sulfate ＜ OM (organic matter). As the secondary ionic aerosols (SIA) and dominant tons, SO_4~(2-), NO_3~- and NH_4~+ all exhibited strong seasonal distributions, consistently with the lowest values in summer and the highest in winter. OM was the most abundant component in PM_(2.5), the lowest concentrations of which were observed in summer at both sites, while the highest concentrations of OC (organic carbon) appeared in winter at WD and autumn at TH, respectively. The highest OC concentration observed in autumn was tightly related to the biomass burning near the suburban site. The crustal elements (Mg, K, Ca and Fe) dominated the 20 detected elements in PM_(2.5), with the highest concentrations in spring in Wuhan, which might be due to frequent sandstorm from north carrying abundant soil dusts in spring in China. Ten trace elements (Cu, Ga, Ag, Tl, Ca, As, Zn, Pb, Se and Cd) were enriched in PM_(2.5) and the higher EF for Ag, Pb, Se and Cd in PM_(2.5) indicated that the air pollution from vehicle exhaust emission and coal burning in Wuhan was serious and noteworthy.