| The Yunnan Plateau（YP）is located in a remote area in Southwest China with relatively clean atmospheric environment.Due to the YP’s unique geographical location connecting to Southeast Asia and the development in recent years,the urban atmospheric environmental problems in the YP are gradually becoming prominent.Therefore,in order to protect the good ecological environment in the YP,the changes of air quality and its influencing factors need to be studied urgently.In this paper,the atmospheric composition observation data of PM2.5,PM10,O3,SO2,NO2 and CO from the environmental monitoring stations in the YP from 2016to 2018 were comprehensively analyzed,the atmospheric chemistry model WRF-Chem and the trajectory model HYSPLIT are used to simulate and analyze the changes of urban atmospheric environmental capacity and atmospheric pollution events for estimating the differences of atmospheric environmental capacity in strong and weak monsoon years in Mengzi city,a border city in the southern YP,and investigating the cross-border transport of air pollutants from Southeast Asia during a springtime particle pollution period in Xishuangbanna City.The objecties of study are to fully understand the variations of urban air quality in the Yunnan Plateau,the influence of Asian monsoon on the interannual variation of urban atmospheric environmental capacity in Yunnan,and the impact mechanism of air pollutants from biomass burning in Southeast Asia on regional air pollution through the transboundary transport of air pollutants.The main contents of this thesis are summarized:1.The Changes of Urban Air Quality over the YP in Recent Years under the Background of Clean Atmospheric EnvironmentFrom 2016 to 2018,the proportion of clean days in all cities of YP reached more than95%.No pollution incidents occurred in Lijiang and Diqing in Northwest Yunnan,while the southern cities of Honghe,Dehong and Xishuangbanna had the lowest proportion of clean days.The number of pollution days in spring is largest in the Yunnan Province,which is more than 2.5 times as that in winter,and the number of pollution days in summer is smallest.The spatial distribution of air quality over the YP is divided into three types:1)the southern region with frequent air polluation;2)Kunming,Zhaotong and Qujing in the northeast YP with moderate air pollution,and 3)the clean northwest region.Over recent years,the ambient concentrations of PM2.5,SO2and CO showed the significant downward trends,with the average annual concentration in 2018 decreased by 10.25%,24.86%and 6.93%respectively compared with 2016,while the O3 concentrations presented an increasing trend year by year,with an annual concentration of 13.26%higher in 2018 than in 2016.The regional average concentrations of PM2.5,PM10,O3,SO2,NO2 and CO concentrations in Yunnan Province are23.75,43.64,54.67,11.70,16.63 ug?m-3 and 0.79 mg?m-3 respectively,presenting the relatively cleaner air environment comparaed with other regions in China.The spatial distribution of air pollutant concentrations and the number of days of pollution are relatively consistent,with higher concentrations in the southern border cities and the central and eastern YP,and lowest concentrations in the northwest YP.The concentrations of air pollutants in northeast and southern YP are the lowest in summer,with the concentrations of PM2.5,PM10,SO2,NO2 and CO highest in winter in northeast YP and highest in spring in south YP（SO2 in autumn）.The concentrations of O3 in both regions are bimodal,with the highest values existing in spring.2.Influence of Anomalous Asian Monsoon Climate on Interannual Variation of Urban Atmospheric Environmental Capacity in YunnanAtmospheric environmental capacity is an important index reflecting the self-purification ability of the atmosphere and the carrying capacity of air pollutants in a certain area.The air quality model WRF-Chem was used to simulate for estimating the atmospheric environmental capacity in Mengzi of the YP influenced by Asian monsoon climate change.We chose 2005 and 2015 respectively as the strong and weak monsoon years according to the normalized South-Asian Monsoon Index.The concentrations of major atmospheric pollutants at all seasons（represented by January,April,July and October respectively）of 2015 and summer（represented by July）of 2005 were simulated,the atmospheric environmental capacities of CO,NO2,SO2,PM2.5 and PM10 in Mengzi were estimated with 120.31、1.127、1.875、1.267、1.688(×104t?a-1),respectively.The atmospheric environmental capacity of major air pollutants was the smallest in winter and the largest in spring excepting PM10.the PM2.5 emissions in winter reached saturation.Compared with the2015 summer with weak monsoon,the atmospheric environmental capacities of CO,NO2,SO2,PM2.5 and PM10 increased respectively by 4.81%,3.86%,12.6%,18.4%and 8.7%in2005 summer with strong monsoon,and the PM2.5 increased most.The interannual variation of the Asian monsoon could exert an important impact on regulating the air quality and atmospheric environmental capacity of the YP.3.Simulation on a Springtime Fine Particle Pollution Period in Xishuangbanna and the Influence of Cross-border transport of Air Pollutants from Southeast AsiaXishuangbanna,on the border of Yunnan Plateau,is close to Southeast Asian.In March2017,a fine particle pollution period occurred,the surface concentrations of PM2.5 observed rose sharply with the daily average concentration exceeding 115ug?m-3.This pollution period in Xishuangbanna was simulated with the air quality model WRF-Chem to analyze the regional transport of air pollutants.The results showed that the cross-border transportof PM2.5emitted from biomass burning in Southeast Asia was the main source of this atmospheric fine particle pollution.In the stage of air pollution formation,air pollutants were mainly imported from Xishuangbanna’s west and south borders.In the ending stage of pollution,air pollutants were exported from the north and east borders.The maximum transport rates in the north and east borders were higher than those of the south and west borders.Through backward trajectory modeling and PSCF analysis,it is concluded that air pollutants were mainly transported from the central and eastern parts of Myanmar.According to the sensitivity test and the statistical characteristics of air mass,the contribution of local emission in this pollution process was only 8.07%.Emissions from northern Myanmar,central and eastern Myanmar,western Laos and northern Vietnam contributed respectively 5.58%,74.01%,10.59%and 1.75%to the air pollution in the YP. |
