Characteristics and formation mechanism of PM2.5 pollution during heavy pollution in an industrial-dominated city in Southwest China
To study the characteristics and formation mechanisms of haze pollution in Changshou District,a typical industrial city in the upper reaches of the Yangtze River,observational analyses of fine particulate matter(PM2.5)and its important precursors were conducted separately in urban and industrial areas during periods of continuous haze pollution.The results showed that the mean concentration of PM2.5 in Changshou District during the observation period was(71.78±38.44)µg/m3,with the highest daily mean reaching 193µg/m3 during haze pollution episodes.Compared to non-polluted periods,various chemical components of PM2.5 increased during haze pollution,with rapid growth of organic matter(OM)and secondary inorganic aerosols(SIAs)being the primary factors contributing to haze pollution.During haze pollution episodes,the sulfur oxidation ratio(SOR)and nitrogen oxidation ratio(NOR)significantly increased,with increases of 64%and 55%,respectively,compared to clean days,and higher relative humidity(RH)environments played a promoting role in the hygroscopic growth of SOR,NOR,and aerosols.Secondary organic aerosols(SOAs)also showed a significant increasing trend during haze pollution periods,with an increase of 13.03µg/m3 compared to clean days.Evaluation of SOAP revealed that aromatics such as toluene,o-xylene,and m-xylene significantly contributed to SOA formation.Principal component analysis(PCA)and Spearman correlation analysis identified three main sources of chemical components in PM2.5,namely industrial sources,crustal sources,and dust sources,with industrial sources being the most important contributor to PM2.5 chemical composition.Source apportionment results indicated that Changshou District and its surrounding areas are important potential source regions for PM2.5,SIAs,total organic carbon(TOC),sulfur dioxide(SO2),nitrogen dioxide(NO2),and total volatile organic compounds(TVOCs),with local emissions from pollution sources playing a crucial role in haze formation.
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