Characterization and source apportionment of carbonaceous PM2.5 particles in China - A review

Organic aerosols (OAs) account typically for 20-90% of fine particles (PM2.5) in the lower troposphere. They contribute to a wide range of environmental problems, from local issues (e.g., urban haze) to global problems (e.g., climate change). Huge efforts have been dedicated to studying the composition, abundance, spatial and temporal distribution and sources of organic aerosols in China. This review aims to summarize recent studies on characteristics and sources of OAs and assesses the current state of understanding of the organic aerosol pollution in China. The OA constitutes ∼20-45% of the PM2.5 with an annual mean value of 5.2-44.5 μg/m3 at sites across China, which is about five times higher than that reported in North America and Europe. There are thousands of different organic compounds in atmospheric aerosols, but only about 5-10% of them have been identified and quantified. OAs show pronounced spatial variations with much higher concentrations in Northern than Southern China. Seasonally, the highest OA concentrations are observed in the winter, whereas the lowest are in the summer. This is due to higher emission rates from anthropogenic sources (e.g., biomass and coal combustion) and poorer dispersion conditions in the winter. Approximately 60-80% of total OA is apportioned by receptor modeling (such as Chemical Mass Balance, CMB) and tracer-yield method, based on the source profiles of primary organic aerosols (POA) and secondary OA (SOA) derived from local emission sources. A number of OA sources are identified, including motor vehicles, industrial emissions, biomass combustion, food cooking, and coal combustion for POA and anthropogenic and biogenic emissions for SOA. Industrial emissions and motor vehicular exhaust are the dominant sources of organic aerosols in the industrialized areas of Northern China, as well as the Pearl River Delta and Eastern China, whereas in other urban areas, residential coal combustion and motor vehicular exhaust are the dominant sources in winter and summer respectively.