Significant Increase of Aromatics-Derived Secondary Organic Aerosol during Fall to Winter in China

Human activities release large amounts of anthropogenic pollutants into the air, and thereby produce substantial secondary organic aerosol (SOA). Aromatic hydrocarbons (AHs) that mainly emitted from coal combustion, transportation, solvent use and biofuel/biomass burning, are a major class of anthropogenic SOA precursors. At present, there are few field studies focusing on AH-derived SOA (SOA_A) on a continental scale, especially in polluted regions of the world. In this study, a one-year concurrent observation of the SOA_A tracer, 2,3-dihydroxy-4-oxopentanoic acid (C₅H₈O₅, DHOPA) was carried out at 12 sites across six regions of China for the first time. The annual averages of DHOPA among the 12 sites ranged from 1.23 to 8.83 ng m^-3 with a mean of 3.48 ± 1.96 ng m^-3. At all observation sites, the concentrations of DHOPA from fall to spring were significantly higher than those in summertime, and positive correlations were observed between DHOPA and the biomass burning tracer (levoglucosan). This indicated that such a nationwide increase of SOA_A during the cold period was highly associated with the enhancement of biomass burning emission. In the northern China, the highest levels of DHOPA were observed in the coldest months during winter, probably due to the enhancement of biofuel and coal consumption for household heating. In the southern China, the highest levels of DHOPA were mostly observed in fall and spring, which were associated with the enhancement of open biomass burning. The apparent increases of DHOPA and levoglucosan levels during the cold period and the negative correlations of visibility with DHOPA and levoglucosan imply that the reduction of SOA_A amount and biomass burning emission is an efficient way to reduce haze pollution during fall to winter in China.