Study On The Characteristics Of Ozone Pollution In Chengdu And Its Relationship With Meteorological Factors

Near-ground ozone was a secondary product of a series of photochemical reactions of nitrogen oxides,carbon monoxide and volatile organic compounds in the atmosphere.Therefore,ozone pollution was closely related to meteorological factors as well as precursors.Based on the monitoring data of ozone concentration at nine environmental air quality monitoring stations in Chengdu from 2015 to 2017,this paper studied the temporal and spatial distribution characteristics of ozone pollution.Combined with the meteorological monitoring data of the same period,the influence of meteorological factors such as solar radiation intensity,temperature,relative humidity,wind direction,wind speed on ozone concentrations was qualitatively analyzed by statistical analysis method.The third generation air quality model Models-3/CMAQ was used to simulate ozone concentrations in summer and winter in typical seasons of Chengdu.The sensitivity of ozone concentrations to main meteorological factors in summer and winter in Chengdu was quantitatively analyzed by scenario analysis method,and the meteorological factors that played a dominant role in ozone pollution in Chengdu were evaluated in order to provide theoretical basis for ozone pollution prevention and control in Chengdu.The main results are as follows:The diurnal variation of ozone concentrations in urban and suburban areas of Chengdu showed a single peak pattern,but the time of peak ozone concentrations appears has obvious regional differences.The peak time of ozone in urban areas in spring,summer,autumn and winter ranged from 16:00 to 17:00.The peak time of ozone in suburban areas in spring,summer and autumn usually occured around 19:00.In winter,the peak time of ozone in urban and suburban areas was about 16:00.The monthly variation trend of ozone concentrations in Chengdu was single peak.O₃ concentrations were higher from May to October,peaks in August.The monthly variation trend of CO and NO₂ concentrations were opposite to that of O₃concentrations.The seasonal variation characteristics of ozone concentrations were as follows:summer>spring>autumn>winter.The spatial distribution of ozone concentrations in Chengdu showed a decreasing trend from north to south,with the lowest concentrations in central urban areas.The spatial distribution of ozone concentrations was mainly caused by photochemistry reaction of ozone precursors emitted from local industrial parks to generate ozone,which migrates and diffuses with the wind direction.Ozone concentrations was positively correlated with total radiation.When the total radiation intensity was greater than 800w·m^-2 the hourly average ozone concentrations was the highest.The ozone concentrations increased with the increase of temperature,and the high value mainly occured in the period when the temperature was higher than 30?.When RH was less than 40%,the hourly ozone concentrations increased slightly with the increase of RH;when RH was more than 40%,the hourly ozone concentrations decreased with the increase of RH.There was a negative correlation between ozone concentrations and atmospheric pressure.The high ozone concentrations in Chengdu mainly occured in the period when the total radiation intensity was greater than 600w·m^-2,the temperature was higher than 30?,the relative humidity was between 40%and 50%,the wind direction was northeast.The sensitivity of average daily maximum 8-hour ozone concentrations to temperature,absolute humidity,atmospheric pressure,wind speed and cloud liquid water content in Chengdu in summer and winter were 0.6271ppb·K^-1 and 0.1624ppb·K^-1,-0.0326ppb·%^-1and-0.0014ppb·%^-1,-0.00335ppb·%^-1 and-0.0016ppb·%^-1,0.00016ppb·%^-1and 0.000156ppb·%^-1,-0.8×10^-5ppb·%^-1 and-0.00117ppb·%^-1,respectively.The sensitivity of ozone concentrations to meteorological factors in summer was as follows:temperature>absolute humidity>atmospheric pressure>wind speed>cloud liquid water content;the sensitivity of ozone concentrations to meteorological factors in winter was as follows:temperature>atmospheric pressure>absolute humidity>cloud liquid water content>wind speed.The spatial distribution of ozone concentrations in Chengdu was uneven in response to the disturbances of various meteorological factors.When the atmospheric temperature increased by 5K,ozone concentrations had the highest response in regions with high pollutant emissions.When the absolute humidity increased by 20%,the average daily maximum 8-hour average ozone concentrations decreased in most areas of Chengdu in summer and winter.When the atmospheric pressure increased by 20%,the average daily maximum 8-hour average ozone concentrations in summer and winter decreased in most areas of Chengdu.When the wind speed increased by 20%,the average daily maximum 8-hour average ozone concentrations in summer and winter in Chengdu increased in some areas and decreases in some areas.When the cloud liquid water content increased by 20%,the average daily maximum 8-hour average ozone concentrations decreased slightly in most areas of Chengdu,but increased slightly in the northern and western parts of Chengdu.