Aromatic hydrocarbons during ozone episode in the Pearl River Delta region, China: Insight into ozone control strategies.

Aromatic hydrocarbons (AHs) are both hazardous air pollutants and key precursors of ozone (O3) and secondary organic aerosols. Understanding the relationship between AHs and O3 is essential for formulating targeted O3 episode control, as AHs exhibit the highest mitigation potential among volatile organic compounds (VOCs). Here, we conducted online monitoring of AHs at an urban site in the Pearl River Delta (PRD) region to characterize AHs, identify their sources, and assess their association with O3 in support of O3 control strategies. The average total mixing ratio of AHs was 6.95 ± 0.51 ppbv during the observation. On O3 episode days, AHs were 44.1 % higher than on non-O3 episode days due to elevated nighttime levels. Positive matrix factorization identified solvent use, vehicle exhaust, and biomass burning as the major sources of AHs, contributing 38.1 %, 23.7 % and 19.8 %, respectively. Cutting solvent use emission was found to be the most effective approach for lowing ambient AHs and reactive species levels, as its accounted for 51.5 %, 51.3 % and 70.7 % of elevated AHs, toluene and xylenes levels during O3 episode days compared to non-O3 episode days. Three O3 sensitivity types were identified based on relative incremental reactivity (RIR) and empirical kinetic modeling approach (EKMA) analyses for O3 episode days. Anthropogenic VOCs with the top RIR-weighted concentration were toluene, m/p-xylene, and o-xylene during both O3 and non-O3 episode days. The analysis of various reduction schemes for three O3 sensitivity types indicate that either AHs or NOx reductions can lead a rapid short-term decline in O3 level, while NOx-focused control strategies offer sustained O3 reduction under minimum collaborative reduction schemes of AHs and NOx in the long-term.