Spatial And Temporal Variation Characteristics Of Air Quality In Lanzhou City Based On Micro-Station Data During The Control Period And Analysis Of The Impact Of Pollution Sources

In recent years,although Lanzhou City has achieved the stage victory of"Lanzhou Blue"by a series of strict measures,fine particulate matter(PM_2.5)pollution has not been fundamentally controlled,while ozone（O₃）,nitrogen dioxide（NO₂）and other pollution factors have gradually become the focus of current pollution control.Therefore,it is important to accurately grasp the spatial and temporal distribution characteristics of ambient air quality and the influencing factors to develop effective pollution prevention and control measures.the COVID-19 swept the world since 2020,in order to stop the spread of the epidemic,Chinese government took a series of emergency control methods,and during this period,human activities were restricted,indirectly reducing the emissions of human pollution sources,which became the best for exploring the influencing factors of environmental air quality"conditions".This study takes the three emergency control periods occurred in Lanzhou City since 2021 as the study period.According to the data from 5 national control points and350 atmospheric environment gridded monitoring points in the main urban area of Lanzhou.The characteristics of changes in air quality index（AQI）and concentrations of six pollutants(PM_2.5,PM₁₀,SO₂,CO,NO₂,O₃)during the control period of human activities are analyzed in time and space,and the effects of main pollution sources on air quality in representative areas during the control period were studied,by using data statistics,characteristic radar analysis,correlation analysis,and spatial statistical analysis methods.The results of the study showed that:（1）From the perspective of time variation,AQI and PM_2.5,PM₁₀,NO₂ and SO₂concentrations were significantly reduced in the main urban area of Lanzhou during the three times of human activities control;PM₁₀ decreased more significantly than PM_2.5,by more than 30%;NO₂ declined by as much as 37.04%during the strict third control period in which motor vehicles were banned;but the rise in O₃ concentration occurred during the first and second control periods.From the air pollution type,the main urban area of Lanzhou City is dominated by complex-type pollution（accumulated and mixed by pollutants emitted from human sources such as restaurants,industries and motor vehicles）before and after the control,and the proportion of vehicle-type pollution significantly decreased or even disappeared due to motor vehicle control.In addition,humidity in winter and temperature in spring and summer are important weather elements affecting the concentration of pollutants in the main city of Lanzhou.（2）From the perspective of spatial changes,During the control period,Significant decrease in AQI in Chengguan District and Anning District;PM_2.5 at restaurants and construction densities dropped,and the PM₁₀ high concentration area changed to low value area with the building construction stopping;O₃ was spread in the main urban area,and the concentration was increased in the whole area;NO₂ concentrations form a high value area in traffic-dense areas,and its concentration drops to a low value area due to human activity control;the control of human activities reduced the area of SO₂high concentration,but had no noticeable effect on the spatial distribution of CO.AQI and air pollutants of all streets in the main urban area of Lanzhou show significant spatial agglomeration before and after human activities control.（3）Based on the change characteristics of air quality in the representative areas of the main pollution sources during the period of control,the treatment of air pollution in Lanzhou from the source should be carried out in several aspects:for particulate matter pollution,the emission of motor vehicles and construction dust should be mainly regulated,while the influence of cooking fumes and industrial emissions should be considered appropriately;For NO₂ and CO,start with motor vehicle and industrial emissions.For SO₂,industrial emissions should be considered.O₃ pollution needs to consider comprehensively the comprehensive effects of cooking fume,motor vehicle emissions and industrial emissions.The cooperation of the target street and the neighboring streets should be considered when making treatment plans for the streets.