海风环流对上海一次臭氧污染过程影响的数值模拟研究

The impact of urbanization and sea breeze on an ozone pollution process in Shanghai

本文针对上海2017年夏季的一次臭氧污染过程,利用WRF-Chem模式模拟了海风环流在臭氧输送、聚集和消散过程中所起的作用.结果表明,白天的海风在沿海区域对500 m高度以下的近地面大气起到清洁作用,但海风环流上支离岸气流也会将海风辐合带的高浓度臭氧输送回到近海的边界层中上部,同时,海风环流和热岛环流的加强效应有助于臭氧前体物(VOC和NO2)在辐合带和近海边界层中上部的聚集,从而加快生成臭氧的光化学反应,进一步地加剧臭氧高值区的臭氧污染.在此基础上设计的敏感性实验分析了城市化和海温的贡献.结果发现,城市化会加重上海地区边界层上部的臭氧污染,白天城市热岛环流对海风环流存在正向叠加作用,增强近地面的向岸风;而海温升高会削弱海风,对臭氧的分布产生很大的影响,进一步证明海风环流在臭氧分布的变化中起到了重要的作用.

Based on WRF-chem simulation results, the impact of sea breeze on ozone′s transportation, accumulation and dissipation during an ozone pollution process in Shanghai, 2017 summer was investigated. The results show that sea breeze can help dilute ozone in the coastal area below 500 m during daytime, but the upper offshore air flow of the sea breeze circulation also transports the high concentration ozone in the convergence zone to the upper and middle part of the coastal boundary layer. Meanwhile, the sea breeze circulation and urban heat island circulation can accumulate ozone precursors in the convergence zone and the upper part of the coastal boundary layer, which can accelerate the photochemical reaction to generate ozone and further intense the ozone pollution in the high concentration ozone area. Two sensitivity experiments were designed to analyze the contribution of urbanization and sea surface temperature. Urbanization can aggravate the ozone pollution in the upper part of the boundary layer. During the daytime, there is a positive correlation between the urban heat island circulation and the sea breeze circulation, which enhances the coastal wind near the ground. Increasing sea temperature weakens the sea breeze and has a great influence on the distribution of ozone.