Spatiotemporal Variations and Source of PM<sub>2.5</sub>in the Sichuan Basin at Nanchong City, China

To evaluate the pollution level, spatial and temporal variations and sources of fine particulate matter (PM 2.5 ) in Nanchong, a city in the Sichuan Basin, China, the trace element concentrations in PM 2.5 were measured.The sources of PM 2.5 were analyzed by the potential source contribution function (PSCF), enrichment factor (EF), and principal component analysis (PCA) methods from December 2014 to April 2016.The results showed that the mean concentrations of PM 2.5 and the analyzed trace elements at the urban sites during the sampling periods were 58.89-63.03g m -3 and 2.81-3.43g m -3 , respectively, and that those at the rural site were 60.134.28g m -3 and 2.55 g m -3 , respectively.There were no significant differences in the mean concentrations of PM 2.5 or the analyzed trace elements between the urban area and the rural area.The seasonal variations in PM 2.5 and the analyzed trace elements in the urban and rural areas were similar, with the order summer<spring<fall<winter. The PSCF analysis showed that the PM 2.5 in the urban area of Nanchong City mainly originated from surrounding areas.The crustal elements K, Ca, Al, Na, Fe, Mg, and Ti were the dominant metals in the urban and rural areas of Nanchong, accounting for more than 93% of the total concentration of the analyzed trace elements.The EF of K was close to 20, indicating that it was derived mainly from anthropogenic sources.The EFs of Ca, Al, Na, Fe, Mg, and Ti were less than 10, indicating that these elements were derived mainly from natural sources.In contrast, although the concentrations of the trace elements Cu, Zn, As, Cd, Se, Ni, Pb, Ba, and Cr were relatively low, the EFs of each of these elements were much higher than 20, suggesting that these elements were mainly derived from anthropogenic sources.The EF and PCA results showed that the PM 2.5 in Nanchong City mainly originates from natural sources, such as soil dust, and anthropogenic sources, such as biomass burning, construction dust, vehicular emissions, firework burning, etc.