[Photochemical Mechanism and Control Strategy Optimization for Summertime Ozone Pollution in Yining City]

To explore the formation mechanism of the ozone （O₃） and emission reduction strategy in a northwestern city， an extensive field campaign was conducted in summertime in 2021 in Yining City， in which the 0-D box model incorporating the latest explicit chemical mechanism （MCMv3.3.1） was applied for the first time to quantify the O₃-NO-VOCs sensitivity and formulate a precise O₃ control strategy in this city. The results showed that： ① the three indicators ［i.e.， O₃ formation potential （OFP）， ·OH reaction rate （k_·OH）， and relative incremental reactivity （RIR）］ jointly indicated that alkenes， oxygenated volatile organic compounds （OVOCs）， and aromatics were the highest contributors among anthropogenic volatile organic compounds （AVOC） to O₃ formation， and the contribution of biogenic volatile organic compounds （BVOC） also could not be ignored. Additionally， the results based on RIR calculation implied that that the acetaldehyde， ethylene， and propylene were the most sensitive individual VOCs species in Yining City. ② The in-situ photochemical O₃ variations were primarily influenced by the local photochemical production and export process horizontally to downwind areas or vertically to the upper layer， and the reaction pathways of HO₂·+ NO and ·OH + NO₂ contributed the most to the gross O photochemical production （60%） and photochemical destruction production （53%）， respectively. Hence， the reduction in local emissions for O₃ precursors was more essential to alleviate O₃ pollution in this city. ③ The outcome based on RIR（NO） / RIR（AVOC） and EKMA jointly suggested that the photochemical regime in this city can be considered a transitional regime that was also nearly a VOCs-limited regime. Detailed mechanism modeling based on multiple scenarios further suggested that the NO and VOCs synergic emission reduction strategies was helpful to alleviate O₃ pollution. These results are useful to provide policy-related guidance for other cities facing similar O₃ pollution in northwest China.