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During winter 2013, extremely high concentrations (i.e., 4–20 times higherthan the World Health Organization guideline) of PM2.5 (particulate matterwith an aerodynamic diameter < 2.5 μm) mass concentrations (24 h samples) werefound in four major cities in China including Xi'an,Beijing, Shanghai and Guangzhou. Statistical analysis of a combined data setfrom elemental carbon (EC), organic carbon (OC), 14C andbiomass-burning marker measurements using Latin hypercube sampling allowed aquantitative source apportionment of carbonaceous aerosols. Based on14C measurements of EC fractions (six samples each city), we found thatfossil emissions from coal combustion and vehicle exhaust dominated EC witha mean contribution of 75 ± 8% across all sites. The remaining25 ± 8% was exclusively attributed to biomass combustion, consistentwith the measurements of biomass-burning markers such as anhydrosugars(levoglucosan and mannosan) and water-soluble potassium (K+). With acombination of the levoglucosan-to-mannosan and levoglucosan-to-K+ ratios, the major source of biomass burning in winter in China issuggested to be combustion of crop residues. The contribution of fossilsources to OC was highest in Beijing (58 ± 5%) and decreased fromShanghai (49 ± 2%) to Xi'an (38 ± 3%) and Guangzhou(35 ± 7%). Generally, a larger fraction of fossil OC was fromsecondary origins than primary sources for all sites. Non-fossil sourcesaccounted on average for 55 ± 10 and 48 ± 9% of OC and total carbon (TC),respectively, which suggests that non-fossil emissions were very importantcontributors of urban carbonaceous aerosols in China. The primarybiomass-burning emissions accounted for 40 ± 8, 48 ± 18,53 ± 4 and 65 ± 26% of non-fossil OC for Xi'an, Beijing,Shanghai and Guangzhou, respectively. Other non-fossil sources excludingprimary biomass burning were mainly attributed to formation of secondaryorganic carbon (SOC) from non-fossil precursors such as biomass-burningemissions. For each site, we also compared samples from moderately toheavily polluted days according to particulate matter mass. Despite asignificant increase of the absolute mass concentrations of primary emissionsfrom both fossil and non-fossil sources during the heavily polluted events,their relative contribution to TC was even decreased, whereas the portion ofSOC was consistently increased at all sites. This observation indicates thatSOC was an important fraction in the increment of carbonaceous aerosolsduring the haze episode in China

Fossil vs. non-fossil sources of fine carbonaceous aerosols in four Chinese cities during the extreme winter haze episode of 2013