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

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