Compositional Variations of Primary Organic Aerosol Tracers of Pm2.5 in Shanghai During the 2019 China International Import Expo

Changes in the characteristics of the primary organic aerosol (POA) tracers in PM 2.5 are closely related to the changes in the corresponding pollution sources. Seven groups of PM 2.5 -bound POA tracers in urban Shanghai were analyzed before (BP), during (CIIE) and after (AP) the second China International Import Expo (October 28-November 17, 2019). Based on the diagnostic ratios of Levoglucosan (Levo) and its correlation with benzo[b]fluoranthene (B[b]F) and benzo[k]fluoranthene (B[k]F), Levo in PM 2.5 came from a mixed source of biomass burning (BB) and coal combustion. Low-molecular-weight n-alkanes (LMW-n-alkanes) were predominantly derived from anthropogenic emissions, while high-molecular-weight n-alkanes (HMW-n-alkanes) showed characteristics of plant-derived emissions. Plant wax n-alkanes (WAX C n ) correlated well with primary sugars (PSs) and sugar alcohols (SAs). The proportions of polycyclic aromatic hydrocarbons (PAHs) with different rings exhibited distinct diurnal variations. The increase in the proportion of HMW-PAHs at night was related to the increase in diesel vehicles. During CIIE, the air quality improved significantly and the concentrations of POA tracers showed a downward trend, but the proportion of POA tracers in PM 2.5 increased. Compared with the period before and after CIIE, the relative concentrations of POA tracers to element carbon (EC) increased by 26.2% and 19.2%, respectively. The proportion of HMW-PAHs increased slightly after CIIE, indicating the recovery of traffic. The percentage change of less than 0 for the relative concentration of SAs was by the dust episode. Among all the compounds measured, the most obvious increase was found in the relative concentration of n-alkanes during CIIE, though the relative concentration of WAX C n decreased, showing that the concentration of n-alkanes from other sources increased significantly. The results suggested that variations in POA tracers can reflect the changes during pollution episodes. While paying attention to the decrease in PM 2.5, it is also necessary to pay attention to the compositional changes in organic aerosols