Wintertime aerosol chemistry in Beijing during haze period: Significant contribution from secondary formation and biomass burning emission

Air pollution in north China is still severe, although Chinese government has exerted great efforts to cut down pollutant emissions in the past decade. To understand the chemistry and sources of the haze particles in north China, PM_2.5 aerosols were collected in Beijing from January 7 to February 27, 2014, during which two haze episodes (haze I and haze II) occurred. The samples were analyzed for water soluble inorganic ions, trace elements, sugars, n-alkane, polycyclic aromatic hydrocarbons (PAHs), fatty acids, dicarboxylic acid, EC (elemental carbon) and OC (organic carbon). Our results showed that relative abundances of primary species such as sugars, PAHs and EC were more abundant on the clean days and the haze I period in Beijing, while secondary aerosols especially secondary inorganic aerosol (SIA)were more abundant in the haze II period. Source apportionment further showed that emissions from cooking (21.6%), road-dust (19.4%), coal combustion (17.8%) and biomass burning (15.4%) were the main sources of PM_2.5 during the clean days, while biomass burning (20.1%) and coal combustion (17.1%) were the main sources during haze I period. For the haze II period, vehicle exhausts (26.9%), secondary aerosol formation (26.6%) and industrial emission (19.1%) were the dominant sources of PM_2.5. Our work suggests that it is indispensable to reduce the emissions from biomass burning and vehicle exhaust in Beijing in order to further mitigate the haze pollution.