Characteristics and source apportionment of PM2.5 during a fall heavy haze episode in the Yangtze River Delta of China

• The pollution exhibited temporal synchronization in the YRD and occurred in a regional scale.
• Organic matter, sulfate, nitrate, and ammonium were the dominant components of PM2.5, and impact the visibility most.
• PM2.5 mainly came from the secondary pollutants and the primary emissions of vehicles and biomass burning in this episode.
• A polluted air mass transported from the north Jiangsu Province and the stagnant meteorology further aggravated the haze.

Joint field observations were conducted from October to November in 2011 to observe haze pollution in the Yangtze River Delta (YRD), China. Samples of particulate matter with diameter less than 2.5 μm (PM2.5) and less than 10 μm (PM10), gaseous pollutants and meteorology data were collected in five cities – Shanghai, Suzhou, Nanjing, Ningbo and Hangzhou – in the YRD. The chemical composition of PM2.5 was analyzed and the light extinction resulting from each chemical species was calculated using the IMPROVE algorithm. A typical heavy haze episode was selected and the chemical mass balance (CMB) model was applied to identify the sources of PM2.5. The average PM2.5 and PM10 mass concentrations during the haze episode were 100 ± 24 μg/m3 and 164 ± 19 μg/m3, respectively; visibility decreased to 1 km. Organic matter (OM), sulfate, nitrate, and ammonium were the dominant components of PM2.5, accounting for 33%, 19%, 17% and 11% of PM2.5 mass, respectively. Sulfate, OM and nitrate had the highest impact on light extinction, contributing 30%, 28% and 19%, respectively. The source apportionment indicate that PM2.5 is primarily from secondary pollutants and primary emissions from vehicles and biomass burning. A polluted air mass from north Jiangsu Province and stagnant meteorology further aggravated the haze pollution. The five cities had similar characteristics and pollution sources.