Abstract:

Sanya is located at the southernmost tip of the Hainan island, with plenty of tourism resources and ecological reservoir. It is one of the most important cities for building an international tourist island and a national ecological civilization experimental zone in Hainan. To understand the characteristics and meteorological causes of a typical ozone (O₃) pollution event occurred in autumn 2019 in Sanya City, this study analyzed the pollutant concentration data released by the Sanya Municipal Bureau of Ecology and Environment, ground observation data, and the ERA5 reanalysis data (the fifth generation ECMWF reanalysis data) from November 1^st to 6^th. The results informed the development of the O₃ pollution early warning, forecasting, and scientific governance. The correlation analysis and backward trajectory model were also used in the study. Results showed that, the values of O₃-8 h (the maximum 8h O₃ concentration) were 162 μg∙m^-3 and 180 μg∙m^-3 on November 4^th and 5^th and were 101.25% and 112.50% above the standard. The O₃-1 h (the maximum 1h O₃ concentration) reached 203 μg∙m^-3 (101.50%) on the 5^th, exceeding the secondary national air quality standard. High O₃ concentration mainly appeared between 14:00 and 19:00. Meteorological conditions of high temperature, low relative humidity, and low speed wind triggered the O₃ pollution process. By analyzing the weather condition, we found that as low-level cold air moved southward and low-level wind field reversed to northeasterly wind, the polluted air mass was transported from north to Sanya City. Moreover, the backward trajectory analysis indicated that the airflow affected by the pollution period mainly came from the inland areas of China. The airflow passed through the Pearl River Delta of Guangdong Province before arriving at Sanya. Results concerning the physical quantity suggested that the low-level airflow, obstructed by the Wuzhishan Mountain, converged in the region of Sanya City. The value of the convergence center was as high as -12×10^-5·s^-1 during the pollution period. In addition, the horizontal wind speed and vertical shear were too weak for O₃ diffusion to occur in Sanya City.

Key words: ozone, ERA5, meteorological reason, weather situation, external transport, Sanya City

摘要：

三亚市位于海南岛最南端,旅游资源丰富,生态环境良好,是海南建设国际旅游岛和国家生态文明试验区的重要城市之一。2019年秋季三亚市出现的一次臭氧（Ozone,O₃）污染过程,为科学认识三亚市此次O₃污染特征及气象学成因,也为进一步开展O₃污染预警预报和科学治理提供技术支撑,利用2019年11月1—6日三亚市生态环境局对外发布的大气污染物数据,以及地面常规观测数据,结合ECMWF发布的第5代资料（the fifth generation ECMWF reanalysis data,ERA5）,采用相关分析和后向轨迹模型对其进行分析。结果表明,11月4日和5日O₃-8 h（臭氧最大8 h滑动平均）分别为162 μg∙m^-3和180 μg∙m^-3,超标百分比为101.25%和112.50%。5日O₃-1 h（臭氧最大1 h平均）达到了203 μg∙m^-3,超标百分比为101.50%。14:00—19:00是O₃质量浓度高值时段,气温偏高,相对湿度偏小,风速偏弱等气象条件的出现促进了此次O₃污染过程的发生。天气形势特征分析表明,低层冷空气扩散南下,低空风场逆转为东北风,有利于北方污染气团向三亚市输送;后向轨迹分析表明,污染时段的影响气流主要来自中国内陆地区,经过广东省珠三角地区到达三亚市。通过物理量场的计算可知,受五指山山脉的阻挡,低层气流绕山辐合明显,污染时段三亚市上空气流辐合中心值高达-12×10^-5·s^-1,加之10 m风速（v_{10 m wind}）和垂直切变较弱,不利于三亚市O₃的扩散。

关键词: 臭氧, EAR5, 气象成因, 天气形势, 外源传输, 三亚市