| Ozone is a kind of light blue gas with special odor.It is an important trace component of atmosphere.Its main source is troposphere transport and tropospheric photochemical reaction.When the near-surface ozone exceeds a certain concentration,it will harm to people and other organisms exposed to the environment for a long time。Since the photochemical event happened in Los Angeles in the 1950s,the study of tropospheric ozone has been started.The study of ozone in China started in the 1980s and mainly concentrated on the eastern coast and inland cities.According to the results of monitoring data released in recent years,the city ambient air quality days ratio above 90%.A variety of factors such as global climate change,urbanization city cause ozone pollution obviously.Ozone has replaced PM100 to influence Lhasa air quality days proportion of main pollutants.As provincial capital city of Tibet,it is great significance for improving atmospheric environmental quality in Lhasa that,Studying the spatial and temporal distribution of near-earth ozone and its precursor,put forward effective prevention.Based on the real-time monitoring data of six automatic monitoring stations of national controlled atmospheric environment in Lhasa from 2013 to 2019,combined with the data of precursor analysis and detection collected in different years.Analyzing the spatial and temporal distribution of ozone in Lhasa,evaluate the correlation between ozone pollution with the spatial and temporal variation trend of the precursor,other environmental meteorological factors influence and contribution to ozone pollution.The following conclusions are drawn:First,The number of days in which ozone was the primary pollutant was much higher than that of particulate matter in 7 years,Lhasa atmospheric pollution appeared a total of 106 days,the number of days with ozone for primary pollutants for 58 days,accounting for 54.7%of the total pollution days,Ozone has obviously become the main factor affecting the proportion of days with good ambient air quality in Lhasa.Second,the trend of inter-annual variation of ozone content in Lhasa is not obvious,and the overall ozone content remains between 130 and 150μg/m3,which is lower than the second-level standard concentration limit（160μg/m3）.The ozone concentrations from 2013 to 2019 are 146,134,142,151,128,136 and 129μg/m3.The concentration fluctuated less in other years except 2016.Third,the ozone content in Lhasa changes obviously with the seasons,and the high ozone value is mainly concentrated in the spring and summer.The order of ozone concentration from high to low is spring,summer,autumn,and winter.In terms of months,the high values are mainly concentrated in April to June.The daily variation of ozone concentration showed a single-peak trend,the lowest concentration appearing at9 am.With the increase of sunshine and temperature,the ozone concentration also increased,and the peak was concentrated from 17 to 19 PM,the highest concentration appearing at 19 pm.With the sunset,the solar radiation weakened and the temperature dropped,and the ozone concentration also decreased.Fourth,from the spatial distribution characteristics of ozone content in Lhasa,the observation point with most days exceeding standard is Lhasa railway station,in order,Bakuojie,District monitoring station,Municipal Environmental Protection Bureau,Tibet University and District radiation station.The ozone concentration of other cities in our province is Shigaze,Lhasa,Shannan,Ali,Changdu,Linzhi,and Naqu from high to low.However,the ozone concentration in Lhasa city is lower than that in Namcuo area and lower than the national average level,but higher than that in Harbin City in high latitude area,which is equivalent to that in Xining City,which is also a plateau city.Fifth,precursors have important influence on the change of ozone concentration,there was a significant negative correlation between ozone concentration and NO2,CO in Lhasa,but no significant correlation between ozone concentration and particulate matter.The composition VOCs in the ambient air of Lhasa is mainly composed of aromatic hydrocarbons,under the influence of atmospheric diffusion conditions,the effect of VOCs on ozone generation is not obvious.Sixth,environmental meteorological factors such as temperature,humidity,wind direction and atmospheric pressure have important influence on the variation of ozone concentration in the near-surface atmosphere.There is a significant positive correlation between ozone concentration and air temperature,a significant negative correlation with relative humidity and air pressure,and no significant correlation with wind speed. |
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