Seasonal and spatial differences in source contributions to PM_2.5 in Wuhan, China

Fine particle (PM_2.5) samples were collected in 2011 and 2012 simultaneously at three sites in Wuhan in an industrial area (ID), downtown Wuhan (DT), and the Wuhan botanical gardens (BG). The annual average concentration of PM_2.5 was highest in the industrial area at 180μgm^-3 and lowest in the botanical gardens, with an average of 93μgm^-3. The average downtown PM_2.5 concentration was 113μgm^-3. All sites had concentrations well above the World Health Organization (WHO) guidelines and the Chinese air quality standard. The concentration of major constituents of PM_2.5 varied seasonally across all sites; specifically, sulfate, nitrate, and organic carbon varied most strongly during spring, followed by summer and fall. Organic carbon varied the most across sites for all seasons, which is attributable to large differences in local source emissions. The major primary sources contributing to OC were vehicle emissions (38.1±8.3%), coal combustion (7.0±6.2%), meat cooking (3.0±1.6%), and biomass burning (3.0±1.0%). All these sources had large seasonal variations across the three sites. Biomass burning had the largest impact at BG, mobile sources had the largest impact at DT, and coal combustion had the largest impact at ID. Mineral dust was a major contributor to PM_2.5 (average 16.8±9.6μgm^-3) and had very homogenous concentrations across the sites during springtime due to regional dust storms, but had much higher concentration at ID during the summer and fall. The results demonstrate the need for both regional and local air pollution control strategies to reduce air pollution in Wuhan. This research contributes to the field of particulate matter studies by providing information about seasonal and regional fluctuations in PM_2.5 in large urban areas, which helps advance understanding of the sources responsible for urban haze.