偏低气温下的O3污染特征及其主要气象成因

针对2013~2019年上海地区气温相对偏低（25℃及以下）的一类O₃污染事件，从时间分布特征、天气系统类型、气象成因等方面进行了深入分析.结果表明：上海近7a偏低气温下的O₃污染按小时标准和日标准分别出现45h和19d，占各自O₃污染总次数的5.0%和7.3%，在春季则上升至20.6%和20.0%，是上海春季主要O₃污染现象之一.当气压介于1010.1~1017.1hPa、风速介于2.1~3.2m/s、湿度介于40.0%~54.0%、辐射介于0.5~2.7MJ/m²，较易出现偏低气温下的O₃污染；与高温下的O₃污染相比，出现偏低气温下的O₃污染时，气压、PM_2.5和NO₂浓度分别偏高了10.0hPa、26.0μg/m³和24.9μg/m³，辐射偏低了0.5MJ/m².造成偏低气温下的O₃污染天气类型可以分为弱高压前部、弱高压控制和海上高压后部3种.3个典型污染个例分析显示，上游输送、本地静稳辐合和垂直逆温条件分别是这3种类型的主要气象成因.

Characteristics and main meteorological causes of ozone pollution under relatively low temperature conditions

The temporal distribution, weather system types and meteorological causes of ozone (O₃) pollution events under relatively low temperature (below 25℃) were analyzed in Shanghai from 2013 to 2019. The results show that O₃ pollution under relatively low temperature occurred 45hours and 19days, respectively according to the hourly and daily standard in Shanghai in recent seven years, accounting for 5.0% and 7.3%, respectively of the total O₃ pollution. The percentage increased to 20.6% and 20.0% in spring, indicating that the O₃ pollution under relatively low temperature was one of the main O₃ pollution phenomena in Shanghai in spring. The O₃ pollution under relatively low temperature was more likely to occur with pressure of 1010.1~1017.1hPa, wind speed of 2.1~3.2m/s, relative humidity of 40.0%~54.0%, and radiation of 0.5~2.7MJ/m². Compared wieh the O₃ pollution under high temperature, the air pressure, PM_2.5 and NO₂ concentrations were 10.0hPa, 26.0μg/m³ and 24.9mg/m³ higher, and the radiation was 0.5MJ/m² lower when the O₃ pollution under relatively low temperature occurred. The O₃ pollution under relatively low temperature can be mainly attributed to three weather system types:the front of weak high pressure, the control of weak high pressure and the rear of offshore high pressure. Analysis of three typical pollution cases showed that upstream transport, local static convergence and vertical temperature inversion conditions were the main meteorological causes of these three types of pollution respectively.