Regional haze formation enhanced the atmospheric pollution levels in the Yangtze River Delta region, China: Implications for anthropogenic sources and secondary aerosol formation.

High-time-resolution (3-hour) PM2.5 samples were collected simultaneously from the rural and urban areas in the Yangtze River Delta region during winter. The aerosol samples were analyzed for carbonaceous components, organic tracers, water-soluble inorganic ions and stable carbon (δ13C) and nitrogen (δ15N) isotopic compositions of total carbon and total nitrogen. The values of PM2.5 and secondary organic carbon (SOC) for both sampling sites were observed 2 times higher in haze events compare to those in clear days, implying severe pollution occurred by photochemical oxidation during haze periods. The PM mass of rural samples showed similar temporal trend and significant correlation with the urban PM, reflecting pollution sources or their formation process are most likely identical. Diurnal variations of PM2.5 and carbonaceous components revealed that pollution levels increased at daytime due to the photochemical oxidation. In addition, SOC and OC were influenced by the relative humidity (RH%) and temperature (T °C), indicating that such meteorological factors play important roles in the occurrence of regional air pollution. The concentrations of levoglucosan, polycyclic aromatic hydrocarbons, hopanes, and n-alkanes were 625 ± 456 and 519 ± 301 ng m-3, 32.6 ± 24.7 and 28.7 ± 20.1 ng m-3, 1.83 ± 1.51 and 1.26 ± 1.34 ng m-3, and 302 ± 206 and 169 ± 131 ng m-3 for rural and urban samples, respectively. Levoglucosan is the most abundant organic compounds, exhibited 2-3 times higher in haze than clear days, suggesting biomass burning (BB) emission substantially affects the haze pollution in winter. Furthermore, NO3- was the dominant ionic species followed by SO42-, NH4+, Cl- and other minor species for both sites. The δ13C and δ15N values demonstrate that anthropogenic activities such as fossil fuel combustion and BB are the major sources for carbonaceous and nitrogenous aerosols. This study implies that both the regional anthropogenic emissions and meteorological conditions influenced the regional haze formation, leading enhancement of pollution levels in eastern China during winter.