Characteristics of Carbonaceous Species in PM2.5 in Wanzhou in the Hinterland of the Three Gorges Reservior of Northeast Chongqing, China

Daily PM2.5 samples were collected in the four consecutive seasons in 2013 in Wanzhou, the second largest city in Chongqing Municipality of China and in the hinterland of the Three Gorges Reservior on Yangtze River and analyzed for the mass concentrations and carbonaceous species of PM2.5 to investigate the abundance and seasonal characteristics of PM2.5, and organic carbon (OC) and elemental carbon (EC). The annual average PM2.5 concentrations were 125.3 μg·m−3, while OC and EC were 23.6 μg·m−3 and 8.7 μg·m−3, respectively. The total carbonaceous aerosol (TCA) accounted for 32.6% of the PM2.5 mass. On seasonal average, the OC and EC concentrations ranked in the order of winter > fall > spring > summer, which could be attributed to the combined effects of changes in local emissions and seasonal meteorological conditions. Strong OC-EC correlations were found in the winter and fall, suggesting the contributions of similar sources. The lowest OC-EC correlation occurred in the summer, probably due to the increases in biogenic emission and formation of secondary organic aerosol (SOA) through photochemical activity. Average secondary organic carbon (SOC) concentration was 9.0 μg·m−3, accounting for 32.3% of the OPEN ACCESS Atmosphere 2015, 6 535 total OC. The average ratios of SOA/PM2.5 of 3.8%~15.7% indicated that SOA was a minor fraction in fine particles of Wanzhou.