| Particulate matter management in the Pearl River Delta(PRD)has been very effective in recent years,but ozone pollution has shown a significant upward trend,especially in autumn.The important synoptic patterns that cause ozone pollution in PRD region in autumn are subtropical highs and typhoons.The study of the evolution characteristics of ozone pollution under these two synoptic patterns will help to understand the meteorological mechanism of ozone pollution formation and provide a scientific basis for the prevention and control of ozone pollution in the PRD region.This study analyzes the spatiotemporal evolution characteristics of ozone in PRD from 2015 to 2020 based on observational data,and divides the subtropical highs and typhoons into 8 related types and 4 types according to the intensity and location of the subtropical highs and the path of the typhoons.After that,the subtropical high-related type and typhoon type with the greatest impact on ozone pollution in the PRD were compared and identified.Further the WRF-CMAQ numerical simulation method is used to study the meteorological causes of the most severe ozone pollution season(autumn 2019)since the official ozone observation occurred in PRD in 2006.Combined with the process analysis method,the contributions of photochemical and transport processes to ozone pollution in PRD under the influence of a subtropical high and the typhoon Mina were quantified.The main results of this paper are as follows:(1)From 2015 to 2020,the ozone concentration and pollution levels in PRD showed an upward trend year by year with the spatial distribution showing a trend of westward and southward expansion from the central PRD.The overall average value reached its highest in 2019 and then showed a decreasing trend towards the north in2020.There were obvious seasonal variations in the distribution of ozone,with the highest overall concentrations in autumn.Areas of high ozone concentration were mainly concentrated in the southwest,and the seasonal variations of spatial distribution matched the seasonal changes of the prevailing monsoon in the PRD.(2)Regarding the synoptic patterns related to the subtropical highs,the number of polluted days and the number of polluted cities are the highest when PRD is influenced by the ridge type within the range of 5880 geopotential meter(gpm)(IN＿SH＿RIG).The greatest probability of ozone pollution occurs when influenced by the eastern side of the subtropical high(E＿SH).Regarding the synoptic patterns related to typhoons,a total of 63 typhoons occurred in the autumn of 2014-2020,and ozone pollution occurred in PRD during 44 of these typhoons.In addition,during the occurrence of northbound or turning typhoons,the number of typhoons,the number of affected days and the corresponding ozone concentration are the ones that have the greatest impact on ozone pollution in PRD.(3)The results of the WRF-CMAQ numerical simulations show that during the early autumn subtropical high and the influence of Typhoon Mina in 2019,the transition of sea-land breezes at night led to the pollutants from the sea back to land and resulted in an increase of about 5.5～8.4ppb in ozone in PRD.Ozone and its precursors stored in the residual mixing layer at night contributed 34%-50% to the increase in ground-level ozone concentration in the following morning.Photochemical production of ozone is found to be the predominant positive contributor(about 7.2ppb/h)to the ozone budget during the entire ozone episode;while the horizontal and vertical transport fluxes are the dominant negative contributors.Our study propose that the enhanced photochemical production of ozone under the conducive influence of a Pacific subtropical high followed by Typhoon Mina in early autumn 2019 is the major cause of the most severe ozone pollution season since the official ozone observation started in PRD in 2006. |
PDF Full Text Request