Simulation Of Atmospheric Environmental Quality System In Jilin City Based On Models-3/CMAQ

With the social progress and economic development,the acceleration of urbanization and the improvement of human living standards,it is inevitable that a series of environmental pollution problems will occur.As the pillar industry area of Jilin Province,Jilin City consumed a lot of resources and therefore generated a large amount of primary or secondary pollutants.At present,the atmospheric environmental pollution problem facing Jilin City is rather severe.In order to explore the characteristics of air pollution in Jilin City,and provide effective reference in the establishment of air pollution prevention and control programs,this paper took Jilin City as the research area,and used Models-3/CMAQ to establish an air quality simulation system suitable for Jilin area.First,this research analyzed the AQI status,the spatial and temporal distribution characteristics of various pollutant concentrations,and the relationship with meteorological factors of Jilin City in 2019 based on the monitoring data.Then,the pollutant simulation plan was determined,the ISAT tool was used to divide the grid of the research area and allocate the inventory,and the WRF-CMAQ simulation system was build,which mainly simulated the concentration of SO₂,NO₂ and PM_2.5in January,April,July and October of 2019 in Jilin City.The simulated and monitored values were evaluated from different dimensions to verify whether the simulation results of the model are meaningful.Finally,combined meteorological factors and backward trajectory to analyze the characteristics of pollutants in December,and set up emission reduction scenarios to simulate the concentration distribution before and after emission reduction.The conclusions are as follows:（1）In 2019,the number of AQI-compliant days in Jilin City was 327,and the number of non-compliant days was 38 days.The air quality was good from May to November.Heavy pollution occurred in January,March,and December.In December,pollution weather occurred for more than one week.（2）Spatial distribution characteristics of pollutants:The overall spatial distribution characteristics of SO₂,NO₂,CO,PM_2.5 and PM₁₀ in Jilin City in 2019 were similar,and the overall trend is gradually increasing from south to north and from east to west.On the other hand,O₃showed a distribution pattern where the concentration in the southeast being higher than in other regions.（3）Temporal distribution characteristics of pollutants:The annual average concentrations of SO₂,NO₂,O₃,CO,PM_2.5 and PM₁₀in Jilin City in 2019 were10.8μg/m³,21.69μg/m³,85.35μg/m³,0.75 mg/m^3,35.37μg/m³ and 59.7μg/m³.Except for the O₃ concentration which was higher in summer,the concentration of other pollutants basically showed the law of higher in winter.The monthly and diurnal variation of O₃ showed a"single peak"pattern,while the remaining several pollutants showed a"double peak"pattern.（4）Analysis of meteorological factors:Different pollutants have different correlations with air pressure,temperature,and customs in different seasons,and temperature and air pressure had a strong correlation with pollutants.The dominant wind directions throughout the year were west-southwest and westerly winds,with wind frequencies of 17.94%and 15.36%,respectively.The dominant wind direction was similar in spring and winter,and the dominant wind direction in summer and autumn was similar.（5）The establishment of the WRF meteorological model in this study can better simulate meteorological variation,and provide more accurate meteorological data for the CMAQ air quality model.The simulated temperature value was slightly higher than the average daily temperature obtained by the weather station,while the simulated pressure value was lower than the actual observed value.Compared with other months,the simulation effect of pressure and temperature was poor,the correlation between simulated values and monitored values was the lowest,while the root mean square error and mean relative error were large in July.（6）The simulated values of SO₂,PM_2.5and NO₂ concentration output by CMAQ were basically consistent with the hourly variation trend of the monitoring data.The simulated value was generally lower than the monitored value.The simulation results of pollutants in January and October were better,while the simulation results in July were relatively poor.The standardized mean deviation and standardized mean error of SO₂ and NO₂ in July were relatively large,and the correlation between the simulation results and the monitored values was relatively small.The high monthly average concentrations of the three pollutants were concentrated in the northwest,southwest and west,while the concentrations in the east and southeast were very low,which was consistent with the spatial distribution of the whole year in 2019.（7）During the period from December 16 to 31,the average wind speed was 1.7m/s,the average temperature was-15.46°C,and the average atmospheric pressure was1028.9hpa.SO₂,PM_2.5and NO₂ had the significant positive correlation with the air pressure and wind speed during this period.The backward trajectory air masses mainly come from the northwest and southwest directions,the concentration of the three pollutants carried by trajectory 7 was the highest,and trajectory 1 has the largest proportion.The distribution of the three pollutants in the research area after emission reduction was basically the same as the concentration distribution before emission reduction.After emission reduction,the areas with large reduction of SO₂ and NO₂concentration were distributed in the southeast direction of Jilin City,while the areas with large concentration reduction of PM_2.5 were distributed in the northwest and southwest direction of Jilin City.