Chemical characteristics of PM2.5 during dust storms and air pollution events in Chengdu,China

Daily fine particulate(PM2.5) samples were collected in Chengdu from April 2009 to February 2010 to investigate their chemical profiles during dust storms(DSs) and several types of pollution events, including haze(HDs),biomass burning(BBs),and fireworks displays(FDs).The highest PM2.5mass concentrations were found during DSs(283.3μg/m3),followed by FDs(212.7μg/m3),HDs(187.3μg/m3),and BBs(130.1μg/m3).The concentrations of most elements were elevated during DSs and pollution events, except for BBs.Secondary inorganic ions(NO3-,SO42-,and NH4+) were enriched during HDs,while PM2.5from BBs showed high K+but low SO42-.FDs caused increases in K+and enrichment in SO42-.Ca2+was abundant in DS samples.Ion-balance calculations indicated that PM2.5from HDs and FDs was more acidic than on normal days,but DS and BB particles were alkaline.The highest organic carbon(OC) concentration was 26.1μg/m3during FDs,followed by BBs(23.6μg/m3),HDs(19.6μg/m3),and DSs(18.8μg/m3). In contrast,elemental carbon(EC) concentration was more abundant during HDs(10.6μg/m3) and FDs (9.5μg/m3) than during BBs(6.2μg/m3) and DSs(6.0μg/m3).The highest OC/EC ratios were obtained during BBs,with the lowest during HDs.SO42-/K+and TCA/SO42-ratios proved to be effective indicators for differentiating pollution events.Mass balance showed that organic matter,SO42-,and NO3-were the dominant chemical components during pollution events,while soil dust was dominant during DSs.