| In recent years,our country’s large urban agglomerations have developed rapidly in terms of economy and industrialization,compound pollution formed by atmospheric particulate matter and ozone has become an important pollution problem in large urban agglomerations.As one of the main urban agglomerations in China,ozone has replaced particulate matter as the primary pollutant in South China.Considering that tropospheric ozone will cause serious harm to human health,ecosystems,and a series of changes in climate warming.Therefore,it is of great significance to carry out this research on the causes and influencing factors of tropospheric ozone pollution in South China.Differential absorption lidar is an active remote sensing technology that detects the temporal and spatial distribution characteristics of atmospheric ozone and aerosols.It can obtain the ozone concentration and aerosol extinction coefficient at the height of the boundary layer.In recent years,because single-point ground-based lidars are subject to regional restrictions,their observation range is also limited.Therefore,differential absorption lidars have evolved from the early single-point ozone monitoring to regional network monitoring,which provides effective data support for the spatial and temporal distribution of regional ozone.In order to understand the vertical change of ozone in South China and its influencing factors,this research is based on the observational data of differential absorption lidar ozone in South China.The seasonal changes of ozone,local pollution and the vertical distribution of regional transmission were analyzed.In addition,the WRF-Chem(Weather Research and Forecasting Model with Chemistry)model was used to retrieve meteorological and ozone precursors,the Shenzhen Meteorological Gradient Tower observed nitrogen dioxide data,and the backward trajectory to explore the cause of ozone pollution.The research shows:(1)The ground-based lidar found that the ozone concentration in autumn in Guangzhou and Jiangmen was significantly higher than that in summer.The high concentration of ozone can reach 1000 m in autumn and 600 m in summer.The daily change of ozone in Yangjiang in summer is not obvious,and the high concentrations of ozone in other cities are mainly concentrated in the afternoon.The average concentration of ozone in summer is the highest in Guangzhou,at 92.57μg/m~3,and the lowest in Dongguan.At the same time,the average ozone concentration in autumn was the highest in Guangzhou,reaching 133.34μg/m~3.In the process of local pollution,high-concentration ozone mainly occurs near the ground.The ozone is evenly distributed above 1500 m.The external transport of ozone mainly occurs at500-1100 m and above 1100 m.The trajectory of the southwesterly airflow is dominant in summer,and the northeast airflow is dominant in autumn.(2)Long-term continuous monitoring of the vertical structure of tropospheric ozone in Guangzhou from January 2017 to September 2018 using differential absorption lidar was carried out.Summer ozone concentration is highest in the four seasons,winter concentration is the lowest,and the difference between spring and autumn is small.In the process of local pollution,high-concentration ozone is mainly concentrated near the ground,and gradually decreases with the increase in altitude.Below 0.7 km,the ozone concentration decelerates faster with the increase in altitude,and the distribution tends to be even at 1.5-2 km.Ozone transmission mainly occurs in the three altitude intervals of 0.3-0.7 km,0.8-1 km,and 1.1 km.(3)Data from September 20 to September 30,2019,lidar,meteorological gradient tower,and WRF model were used to analyzed the temporal and spatial distribution of ozone,the correlation between ozone and extinction coefficient,and the meteorological factors of ozone pollution.The results showed that the daily changes of ozone were significant before the 24th,and there were obvious residual phenomena at night after the 24th,and the concentration of particulate matter in the boundary layer increased significantly.Below 980 m,ozone and the extinction coefficient are negatively correlated,around 290 m-2400 m,both are positively correlated.As the height increases,the concentration of nitrogen dioxide gradually decreases and is accompanied by an increase in ozone concentration.When the temperature is 291.3-301.8 K,the humidity is 19.4%-71.6%,the atmospheric pressure is 903.72-963.1 h Pa,the average wind speed is 4-5.2 m/s,and the main wind direction is northerly,which is beneficial to the high concentration of ozone in Shenzhen.form.The transmission of ozone pollution in Shenzhen this time mainly came from inland cities in the northeast of China,and the contribution from the southeast of Jiangxi Province exceeded 180μg/m~3.(4)The correlation of the city’s near-ground ozone concentration is related to distance.The correlation between adjacent cities(Guangzhou,Jiangmen,Dongguan,Shenzhen)is relatively high.The transmission of atmospheric ozone at vertical height has a higher impact than near-ground ozone transmission.Among them,the overall correlation is highest at 500 m.In summer,the main transmission channels are Ocean–Huizhou–Dongguan–Guangzhou-Jiangmen,Ocean–Yangjiang–Maoming-Southeast of Guangxi Province and Ocean–Chaozhou-Fujian Province.The autumn airflow mainly originates from the inland areas of my country,and the main transmission paths are as follows:the western area of Chenzhou,Hunan–Zhaoqing-Yangjiang,Chenzhou–Qingyuan-Guangzhou-Jiangmen,Jiangxi,Ganzhou–Heyuan–Huizhou-Shenzhen,and atmospheric ozone is transported with the air flow from the western region of Longyan,Fujian Province to Chaozhou.In summer,the transportation volume of Jiangmen City to Guangzhou is higher than that of Shenzhen City,and the maximum transportation flux reaches 1147.82μg/(m~2·s).For Guangzhou and Dongguan,the overall performance below 500 m is conveyed in the direction of Guangzhou like Dongguan.Affected by the northerly airflow in autumn,the horizontal transmission of ozone is from northern cities to southern cities.Guangzhou has a greater impact on the horizontal transmission of ozone in Jiangmen,with the maximum transmission volume of 2752.78μg/(m~2·s). |
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