Composition of photochemical consumed volatile organic compounds and their impact on ozone formation regime: A case study in Zibo, China

Abstract

The transport of volatile organic compounds (VOCs) to the measurement site leads to significant photochemical consumption, directly impacting ozone (O₃) formation. To address this issue, a comprehensive observation campaign was conducted from May 1 to September 30, 2021, in Zibo, China. Using the Framework for 0-D Atmospheric Modeling (F0AM), the impact of photochemical consumed VOCs (C-VOCs) on O₃ sensitivity was evaluated based on initial VOCs (In-VOCs). The results indicate that the average concentration of C-VOCs was 5.8 ± 8.3 ppbv, accounting for 9.5% of the In-VOCs concentration during high-O₃ periods, which was higher than that during low-O₃ periods. Alkenes (including isoprene) contributed 84.6% to the C-VOCs and accounted for 91.0% of the C-OFP (ozone formation potential (OFP) of C-VOCs), followed by aromatics. Isoprene, 1,3-butadiene, m/p-xylene, 1-butene, and propylene were identified as key species contributing to C-OFP. Three methods assessed the impact of including or excluding C-VOCs on O₃ formation. Based on the VOCs/NO_x indicator, the proportion of the NOₓ-limited regime was underestimated by 14%∼21% for the high-O₃ periods and 18%∼21% for the low-O₃ periods without considering C-VOCs. Compared to the results of the measured VOCs (M-VOCs), the relative incremental reactivity (RIR) value of NO_x increased significantly for both high and low-O₃ periods when considering C-VOCs, while the RIR value of anthropogenic volatile organic compounds (AVOC) showed a reverse trend. The RIR(NO_x)/RIR(AVOC) results indicated that the O₃ formation regime shifted from VOC-limited or transitional to NO_x-limited, which is consistent with the result from the empirical kinetic modeling approach (EKMA). Emission reduction modeling suggested reducing AVOC and NO_x at a 1:3 ratio as an effective O₃ mitigation strategy. This work reveals that the NO_x limitation in controlling O₃ generation in this region will be underestimated without considering C-VOCs, emphasizing the importance of C-VOCs in the formulation of O₃ reduction strategies.