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