[Ozone Pollution Characteristics and Formation Mechanism in a Typical Tropical Seaside City]

To investigate the pollution characteristics and formation mechanism of ambient air ozone(O₃) in a typical tropical seaside city, we conducted an observational experiment on O₃ and its precursors at an urban site in Haikou, Hainan Province, from June to October 2019. The O₃ pollution characteristics were analyzed comprehensively; the O₃-NO-VOCs sensitivities and key precursors were determined, and the control strategies for O₃ pollution were carried out. The results were as follows:1 O₃ pollution in Haikou mainly occurred in September and October, with daily maximum 8-h O₃ concentrations in the range of 39-190 μg·m^-3, and the daily variation in O₃ was unimodal, peaking at approximately 14:00. 2 The concentrations of NO₂ and VOCs were higher during O₃ pollution episodes than their respective mean values in Haikou City. The increased O₃ precursor concentrations were an important factor leading to O₃ pollution, whereas O₃ pollution was also influenced by regional transport, with pollutants mainly transported from the northeastern part of Haikou City. 3 O₃-NO-VOCs sensitivity in Haikou City was in the VOCs and NO transitional regime, and the most sensitive precursors in various months were different. O₃ formation in September was sensitive to anthropogenic VOCs the most; however, in October it was sensitive to NO. 4 In the future, the reduction ratio of VOCs to NO should be 1:1-4:1 to control O₃ pollution effectively in Haikou.