Source apportionment and secondary organic aerosol estimation of PM2.5 in an urban atmosphere in China

PM2.5 is the key pollutant in atmospheric pollution in China. With new national air quality standards taking effect, PM2.5 has become a major issue for future pollution control. To effectively prevent and control PM2.5, its emission sources must be precisely and thoroughly understood. However, there are few publications reporting comprehensive and systematic results of PM2.5 source apportionment in the country. Based on PM2.5 sampling during 2009 in Shenzhen and follow-up investigation, positive matrix factorization (PMF) analysis has been carried out to understand the major sources and their temporal and spatial variations. The results show that in urban Shenzhen (University Town site), annual mean PM2.5 concentration was 42.2 mu g m(-3), with secondary sulfate, vehicular emission, biomass burning and secondary nitrate as major sources; these contributed 30.0%, 26.9%, 9.8% and 9.3% to total PM2.5, respectively. Other sources included high chloride, heavy oil combustion, sea salt, dust and the metallurgical industry, with contributions between 2%-4%. Spatiotemporal variations of various sources show that vehicular emission was mainly a local source, whereas secondary sulfate and biomass burning were mostly regional. Secondary nitrate had both local and regional sources. Identification of secondary organic aerosol (SOA) has always been difficult in aerosol source apportionment. In this study, the PMF model and organic carbon/elemental carbon (OC/EC) ratio method were combined to estimate SOA in PM2.5. The results show that in urban Shenzhen, annual SOA mass concentration was 7.5 mu g m(-3), accounting for 57% of total organic matter, with precursors emitted from vehicles as the major source. This work can serve as a case study for further in-depth research on PM2.5 pollution and source apportionment in China.