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 (O) and secondary organic aerosols. Understanding the relationship between AHs and O is essential for formulating targeted O 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 O in support of O control strategies. The average total mixing ratio of AHs was 6.95 ± 0.51 ppbv during the observation. On O episode days, AHs were 44.1 % higher than on non-O 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 O episode days compared to non-O episode days. Three O sensitivity types were identified based on relative incremental reactivity (RIR) and empirical kinetic modeling approach (EKMA) analyses for O episode days. Anthropogenic VOCs with the top RIR-weighted concentration were toluene, m/p-xylene, and o-xylene during both O and non-O episode days. The analysis of various reduction schemes for three O sensitivity types indicate that either AHs or NOx reductions can lead a rapid short-term decline in O level, while NOx-focused control strategies offer sustained O reduction under minimum collaborative reduction schemes of AHs and NOx in the long-term.