Source directional apportionment of ambient PM2.5 in urban and industrial sites at a megacity in China

Refined source apportionment plays an important role in precise control of atmospheric particulate matter sources. PM2.5 samples were collected and analysed in Tianjin from February to October 2016, and directional contribution of individual source category was apportioned by applying a new approach. Results indicated that the mean concentration of PM2.5 was 64 mu g/m(3) during the studying period. NO3- and OC were dominated species in PM2.5 mass. The concentrations of OC and Cl-, and OC/EC were higher in winter than other seasons. Secondary sources (SS), coal and biomass burning (CBB), vehicle exhaust (VE), crustal dust (CD), and industrial emission (IE), were identified as major sources using the PMF model, their contributions to PM2.5 were 28.6-38.1%, 17.3-20.1%, 21.1-23.5%, 10.9-14.2%, and 4.0-10.3%, respectively. The contributions of dust source and coal combustion in Tianjin are decreasing, while that of motor vehicles is gradually highlighted. The contribution of secondary sources is maintained at a high level in recent years. Source contributions from the directions 1-3 (SW, NW, NE) for SS (16.8%, 8.5%, 4.0%), CBB (10.1%, 8.5%, 2.0%), VE (8.7%, 7.9%, 3.2%), CD (7.3%, 7.0%, 0.9%), and IE (4.2%, 3.8%, 1.4%), were observed at TG site. Source contributions from the directions1-4 (SW, WNW, NNW, NE) for SS (16.5%, 9.7%, 5.9%, 6.3%), CBB (8.0%, 5.0%, 2.5%, 1.9%), VE (8.5%, 6.8%, 3.5%, 3.3%), CD (5.9%, 3.2%, 2.0%, 1.0%), IE (2.0%, 0.9%, 0.6%, 0.6%), were observed at FK site. The contributions of major sources from SW direction were higher than other directions.