成都平原城市群夏季臭氧污染天气形势与潜在源分析

Objective Weather Classification and Potential Source Analysis of Ozone Pollution during Summer in Chengdu Plain Urban Agglomeration

通过分析成都平原城市群8个城市2015-2019年夏季地面臭氧污染特征表明,近5年夏季平原O_(3)污染区域呈扩大趋势,成都市O_(3)_8 h第90百分位浓度和超标日数均为最大,雅安、绵阳浓度较低但上升趋势显著。利用PCT客观天气分型方法,对近5年夏季成都平原及周边的位势高度场进行分型研究,结果表明:(1)700 hPa臭氧污染天气形势为高压型,500 hPa为西风槽后和平直纬向型,100 hPa为南亚高压中部和东部型;(2)近5年夏季典型O_(3)污染过程的高低空天气形势为西风槽后部、高压发展和高压控制型,污染过程期间成都平原多受到西风槽后西北气流或副热带高压脊线附近下沉气流的影响;(3)污染天气型具有高温低湿,小风强辐射,白天混合层高的特征。气流下沉增温和局地环流的作用抑制了污染物向高层扩散,促使边界层上部O_(3)下传并堆积于成都平原地区。采用HYSPLIT后向轨迹模式和潜在源贡献法(PSCF),探讨了不同天气型影响下成都平原O_(3)浓度输送的轨迹聚类和潜在源区。结果表明,本地和盆地城市之间的输送对臭氧污染有重要贡献。最主要的臭氧潜在源区位于本地城区,成都、眉山和资阳臭氧潜在源区还集中在川南北部和重庆西部,德阳集中在成都、眉山一带。西风槽后和高压发展型影响下臭氧区域输送表现比较明显,高压控制天气型臭氧呈本地积聚性较显著。

The analysis of the surface ozone pollution in 8 cities in the Chengdu Plain urban agglomeration during the summer of 2015 to 2019 showed that the O_(3)pollution area in plain has expanded in the summer of the past 5 years.The 90th percentile concentration of O_(3)_8 h and O_(3)over-standard days in Chengdu are both the largest,Ya'an and Mianyang have lower concentrations but a significant upward trend.Using PCT objective weather classification method,the geopotential height field of different layers over Chengdu Plain and its surrounding were objectively classified in the summer for the past five years,the results showed that:(1)The 700 hPa ozone pollution weather classification was the high pressure system type,and the 500 hPa was the rear of the westerly trough and the flat vertical zonal type,and the 100 hPa was the central and eastern of asia high type;(2)The high and low altitude weather conditions of the typical ozone pollution process in the summer of the past 5 years are divided into the rear of the westerly trough,high pressure development and high pressure control type.During the pollution process,Chengdu Plain is mostly affected by the northwest airflow behind the westerly trough or the sinking airflow near the ridge of the subtropical high pressure;(3)The polluted weather pattern had the characteristics of high temperature and low humidity,strong radiation in small winds,and high mixed layer during the day.The effects of airflow subsidence and warming and local circulation inhibit the diffusion of pollutants to upper layers,and promote the downward transmission of O_(3)in the upper boundary layer and accumulation in the Chengdu Plain.Using HYSPLIT backward trajectory model and potential source contribution analysis(PSCF),explored the trajectory clustering and potential source areas of different weather patterns that affect the O_(3)concentration in the Chengdu Plain.The results showed that the local and transportations among cities in the Sichuan Basin contribute to the ozone pollution.The most important potential source of ozone is located in the local urban area.The main potential source areas of Chengdu,Meishan and Ziyang are also concentrated in northern Sichuan and western Chongqing,while the main source of Deyang is concentrated in Chengdu and Meishan.The rear of the westerly trough and high-pressure development,the regional transport of ozone is more obvious,and high-pressure control type shows significant local accumulation.