Chemical characteristics and source apportionment of PM2.5 in Wuhan, China

Continuous online measurements of fine particulate matter mass (PM2.5) and its chemical composition were carried out at an urban monitoring site in Wuhan from March 2017 to February 2018. The PM2.5 mass concentration ranged from 6.3 to 223 μg/m3, with the highest in winter and the lowest in summer. Water soluble ions (WSIs) were the most abundant component in PM2.5 (28.8 ± 22.9 μg/m3), followed by carbonaceous aerosol (11.9 ± 10.4 μg/m3) and elements (5.5 ± 6.7 μg/m3). It is noteworthy that six episodes of sustained high PM were observed during the study period. Five major contributors of PM2.5 were identified by positive matrix factorization (PMF) to be the iron and steel industry, fugitive dust, secondary photochemistry, traffic-related emission and biomass burning, contributing 26.3%, 5.5%, 29.5%, 29.2% and 9.6% to PM2.5, respectively. Furthermore, conditional probability function (CPF), trajectory analysis and potential source contribution function (PSCF) were used to identify the influences of local activities and regional source. Local sources mainly include Wuhan iron and steel group, construction sites and urban trunk roads, etc. Three pollution transport pathways of PM2.5 in Wuhan were identified to be northwest, east and south pathway, with the relative contribution of 40%, 17% and 43%, respectively. Western Henan, northern Shaanxi and southwestern Shanxi were identified to be the major potential source regions of PM2.5 in Wuhan.