Characteristics And Influence Mechanism Of Atmospheric Capacity Based On Box Model In Wenjiang District,Chengdu City

At present,China’s environment quality has been generally improved.However,some regions still experienced severe air pollution.In order to further improve the quality of the air environment while ensuring economic development,more reasonable control policies need to be formulated based on the capacity of the air environment.Taking Wenjiang District of Chengdu City as an example,based on the data of air pollution sources,pollutant concentrations and meteorological monitoring data,this study evaluates the ambient air quality index,the primary pollutants and pollutants exceeding the standards.Then the influencing factors of the ambient air quality index are explored based on correlation analysis.Secondly,based on the single box model,this study constructs an assessment system related to the remaining air environment capacity in Wenjiang District,and explores the influencing factors of the remaining air environment capacity.Finally,based on the"13th Five-Year Plan"and"14th Five-Year Plan",this study sets up socio-economic development scenarios to project the atmospheric capacity of Wenjiang District.The results can provide scientific support and suggestions for the future pollution control policies in Wenjiang District.The conclusions of the study are as follows:（1）Wenjiang District emitted 18.49 tons of sulfur dioxide,105.44 tons of nitrogen dioxide,151.54 tons of respirable particulate matter（particle size less than 10 microns）,269.49 tons of carbon monoxide,125.27 tons of fine particulate matter（particle size less than 2.5 microns）,and 8251.97 tons of volatile organic compounds in 2017.During2016-2020,the air quality of Wenjiang District changed from mild pollution to good.While,the primary pollutants in Wenjiang District were mainly PM_2.5and O₃,with a steady increase in the number of days without primary pollutants.The excessive pollutants are mainly PM_2.5and O₃,followed by PM₁₀.（2）Except for SO₂,NO₂,PM₁₀,CO,and PM_2.5showed the steady fluctuation trend from 2016 to 2020,charactered by higher at the beginning of the year,lower in the middle of the year and higher again at the end of the year.O₃showed a opposite change trend,which was lower at the beginning of the year,peaked in the middle of the year and lowered again at the end of the year.The ambient air quality index is highly positively correlated with PM₁₀and PM_2.5and least correlated with O₃.The AQI was negatively correlated with temperature,humidity and wind speed,and positively correlated with air pressure.Except for O₃,all pollutants had positive correlations with each other.（3）During the study period,only the residual atmospheric environmental capacity（RAEC）of SO₂and CO were positive under the daily time scale,and the RAEC of PM_2.5was generally at a low level.The daily average values of RAEC showed a pattern consistent with the pollutant concentrations.Under the monthly time scale,only the RAEC of PM₁₀and PM_2.5had negative values.SO₂and CO were at high levels.NO₂did not have negative values,but its variation was more fluctuating.On the annual timescale,the RAEC of SO₂,NO₂,and CO did not have significant change.PM₁₀and PM_2.5increase year by year,but the total amount of PM_2.5remains low.The RAEC of SO₂had high positive correlation relationships with wind speed and mixed layer height,and low correlation with wind direction and C_P（equilibrium concentration of pollutants in the box model）.The RAEC of NO₂shows the largest negative correlation with its C_Pand high positive correlation with mixed layer height and wind speed.RAEC of PM₁₀also had high negative correlation with C_P.RAEC of CO had the highest positive correlation with mixed layer height,with a correlation coefficient of 0.924^**.RAEC of PM_2.5has the highest correlation with its C_PThe RAEC of SO₂and CO are mainly impacted by meteorological conditions,such as mixed layer height and wind speed,while the RAEC of NO₂,PM₁₀and PM_2.5are mainly impacted by pollutant concentrations,such as background and C_Pvalues.（4）In the scenario analysis,under the baseline development scenario,when the meteorological factors are unfavorable,the RAECs of SO₂,NO₂,PM₁₀,CO,PM_2.5were3675 t/a,1225 t/a,1366 t/a,is 68683 t/a and 660 t/a,respectively.When the meteorological factors are favorable,the RAECs of SO₂,NO₂,PM₁₀,CO,PM_2.5were 15211 t/a,5070 t/a,5655 t/a,is 284279 t/a and 2730 t/a,respectively.When meteorological factors are favorable,none of which has negative values.In a high-speed development scenario,when the meteorological factors are unfavorable,the RAECs of SO₂,NO₂,PM₁₀,CO,PM_2.5were3780 t/a,1241 t/a,1913 t/a,is 72348 t/a and 971 t/a,respectively.When the meteorological factors are favorable,the RAECs of SO₂,NO₂,PM₁₀,CO,PM_2.5were 155,644 t/a,5135 t/a,7920 t/a,is 299447 t/a and 4019 t/a,respectively.When meteorological factors are favorable,none of which has negative values.Meteorological conditions have a significant effect on RAEC under all scenarios.When meteorological conditions are favorable,the RAECs of pollutants are at high levels.However,the RAEC of NO₂,PM₁₀and PM_2.5are all at low levels under the unfavorable meteorological conditions.This indicates that when relatively adverse meteorological conditions are encountered,NO₂,PM₁₀and PM_2.5are all at high risk to induce pollution events.The effort should be given on the reduction of these three air pollutants.