Sources of secondary organic aerosols in the pearl river delta region in fall: Contributions from the aqueous reactive uptake of dicarbonyls

1) CMAQ model performance enhanced with addition of dicarbonyl SOA source. 2) 75% of total SOA was biogenic for the PRD in fall and isoprene was the most important precursor. 3) The irreversible uptake of dicarbonyls by aqueous particles was an important SOA formation pathway in the PRD in fall. We compared our model findings regarding the SOA sources in the PRD in fall with previous SOA source studies based on measurements in the PRD. Hu et al. found that 80%-90% of summertime SOA in Hong Kong was biogenic, but they found much larger contributions from monoterpenes and β-caryophyllene than from isoprene. This may be due to their samples collected in Hong Kong in summer experiencing stronger emissions of monoterpenes and β-caryophyllene. Ding et al. found aromatics to be the dominant source of the identified SOC in central PRD in summer, fall, and winter. Both Hu et al.²⁰ and Ding et al. ²¹ were based on SOA chemical tracer analyses. A main uncertainty in such analyses is that the ratio of a specific chemical tracer mass relative to total SOA (or SOC) mass is assumed constant, which may not be valid under all conditions (e.g., low- or high-NO_x, at low or high OA concentrations and acidity). Hu et al. ²² and Ding et al. ²¹ pointed out that biomass burning emissions contributed significantly to SOA in the PRD. We also found this to be the case through the comparison between simulated SOA and observed OOA (Fig 2), although our model was unable to capture the spatiotemporal variability of biomass burning emissions and their full contribution to SOA.