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

Abstract

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 O3 pollution area in plain has expanded in the summer of the past 5 years.The 90th percentile concentration of O3_8 h and O3 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 O3 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 O3 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.

Keywords

• ozone pollution
• weather classification
• back trajectory cluster analysis
• potential source contribution
• chengdu plain