Chemical reactivity of volatile organic compounds and their effects on ozone formation in a petrochemical industrial area of Lanzhou, Western China.

Measurements of ozone (O) and its precursors were performed in the summer of 2019 in Lanzhou, a petrochemical industrial city, to better understand the reactivity of volatile organic compounds (VOCs) and their effects on O production. During the campaign, the daily maximum 8-hour average (MDA8) O, NO, and total VOC (TVOC) concentrations reached 72.2 ± 19.9 ppb, 24.9 ± 10.8 ppb, and 50.8 ± 46.1 ppb, respectively. Alkanes, alkenes, halocarbons, aromatics, and alkynes contributed 45.3%, 24.0%, 16.5%, 10.0%, and 4.2% to TVOCs, respectively. The OH reactivity and relative incremental reactivity (RIR) of VOCs at different times were calculated. The results indicated that alkenes played a predominant role, accounting for an average of 68.5% of the initial VOC reactivity. Compared to other regions, alkenes are relatively more important for O formation in the petrochemical industry area of Lanzhou, while aromatics are relatively less important. Generally, O formation occurred in a VOC-limited regime in the morning and in a transitional regime in the afternoon. The response surface methodology (RSM) combined with a chemical box model was applied to obtain relationships between O and its precursors and determine the most effective way to reduce the O concentration. Reduction in the non-alkene concentration slightly affected the O concentration. In contrast, the effect of nitrogen oxides (NO) was closely related to the alkene concentration, and NO concentration reduction could lead to an increase in the O concentration when alkenes were abated to less than 80% of the present concentration. To mitigate O pollution near the petrochemical industrial area of Lanzhou, reducing the alkene concentration, especially the C4 alkene concentration (1,3-butadiene, cis-2-butene, and trans-2-butene), was the fastest and most effective control strategy. The results of this study serve as a reference for O pollution control in petrochemical industrial areas.