Abstract:

In mid-to-late July 2022, there was a large-scale and continuous hot climate anomalies occurred in Fujian Province. The daily maximum temperature in Fuzhou City reached 41.9℃ on July 24^th, breaking the record since 1961. At the same time, there were two ozone (O₃) pollution processes in the coastal areas of Fujian Province occurred from July 11^th to 17^th and July 22^nd to 31^st. Fuzhou had exceeded the standard for 4 days in the first pollution process; In the second process, a 2-day level II and a 3-day level I control measure were implemented due to major social events, but O₃ mass concentration had been over grade II for one day. Based on the hourly environmental monitoring, meteorological observation, and meteorological reanalysis data, we used synthetic comparison, synoptic diagnosis, correlation analysis and backward trajectory simulation to characterize the ozone pollution process and analyze its causes during mid-to-late July 2022 in Fuzhou City. Our results will provide technical support for carrying out warning, forecast and management of ozone pollution in summer in the southeast coastal region of China. The results showed that the maximum daily eight-hour average of ozone in Fuzhou City abnormally increased to 141.2 μg·m^-3, which was 1.7 times of the multi-year average value (84.8 μg·m^-3). The hourly value of O₃ mass concentration was significantly higher than the multi-year average value, and there was a “straight peak” phenomenon between 12:00 and 17:00, when O₃ mass concentration reached the second peak around 17:00 (“tail lifting” phenomenon). The backward trajectory analysis indicated that the airflow affected by the pollution period mainly came from the central and southern regions of Fujian Province. The horizontal transport of ozone and its precursors superimpose on the local ozone was an important reason for the occurrence of “tail lifting”. The cause of abnormal increase of O₃ mass concentration and exceedance days was complex. The extreme high temperature, caused by the continuously increased subtropical high area and intensity. The occurrence of the central La Niña event was conducive to the local generation of ozone. In addition, the vertical sinking dynamic transport of the subtropical high thermal dome and ozone in the boundary layer, the horizontal transport of ozone from the upstream region in the afternoon and adverse meteorological conditions played important roles in the ozone pollution.

Key words: extreme high temperature, synoptic situation, vertical conveying, O₃ exceeds the standard, Fuzhou City

摘要：

2022年7月中下旬，福建省出现了1次大范围、持续性的高温过程，24日福州市日最高气温达41.9 ℃，打破1961年以来的历史记录。与此同时，福建省沿海地区出现了2次臭氧（O₃）污染过程（7月11-17日和7月22-31日），省会福州市在第1个污染过程中出现4 d O₃超标，在第2个过程中因重大社会活动保障期间实施了2 d二级和3 d一级的管控措施，但O₃质量浓度仍维持在高位并出现1 d超标。利用环境监测、气象观测及气象再分析资料等，采用合成对比、天气学诊断、相关分析、后向轨迹模拟等方法，详细分析了2022年7月中下旬福州市O₃质量浓度异常升高及其影响因素，以期为进一步开展中国东南沿海区域夏季O₃污染防治、预警预报及与周边地区联防联控提供技术支撑。结果表明：2022年7月中下旬福州市O₃日最大8 h滑动平均值异常升高达到141.2 μg·m^-3是多年平均值（84.8 μg·m^-3）的1.7倍。O₃质量浓度小时值较多年平均值明显偏高且在12-17时出现了一段“峰顶平直”现象，并在17时前后达到第2个峰值（“翘尾”现象）；后向轨迹分析表明，污染时段的影响气流主要来自福建省中部和南部地区，外来输送的O₃及其前体物叠加本地O₃的累积是“翘尾”现象发生的重要原因。O₃污染过程持续发展的最直接原因是在中部型拉尼娜（La Niña）事件的气候背景下，副热带高压面积持续偏大、强度偏强导致极端高温长时间维持，这有利于O₃的本地生成；副热带高压热穹顶和边界层O₃垂直下沉动力输送、上游区域午后O₃水平输送、不利的气象条件等多种因素都对O₃污染的发生都有着重要影响。

关键词: 极端高温, 天气形势, 垂直输送, O₃超标, 福州市