A Study On Characteristics Of Air Pollution And Potential Source Areas Of Particulate Matter In The Key Cities Of Northwest Gansu Province

With the acceleration of China's industrialization and urbanization and large consumption of energy in China,the problem of environmental air pollution is becoming increasingly serious,which has a significant impact on the ecological environment,human health and social and economic development.Air pollution has also become a serious environmental issue that have been drawn much attention and urgently need to be addressed by the government and the public.Jiayuguan,Jinchang and Lanzhou,located in the regions of northwestern China,are the key cities along the ancient silk road and play a vital role in promoting cultural,economic and trade exchanges between the East and the West.Therefore,this paper selected six conventional air pollutants(PM₁₀,PM_2.5,NO₂,SO₂,O₃,CO)in Jiayuguan,Jinchang and Lanzhou from 2014 to 2017 as the air quality evaluation indictors.Based on clarifying and analyzing the pollution characteristics of each pollutant in different time scales,the air quality assessment model was constructed by using the fuzzy comprehensive evaluation method to analyze and evaluate the current status of air quality.In addition,three cities are where sand and dust storms from East Asia pass.Particularly,sand and dust storms that occur frequently during the spring in the arid and semi-arid regions of northwestern China can significantly increase PM₁₀ loadings in the local area and its surroundings.Therefore,in this paper,Hybrid Single Particle Lagrangian Integrated Trajectory model?HYSPLIT?and trajectory cluster analysis?TCA?were used to identify the major transport pathways of PM₁₀,potential source contribution function?PSCF?and concentration-weighted trajectory?CWT?were used to identify the potential dust source areas,and trajectory sector analysis?TSA?was used to quantify regional transported contributions.The particulate air pollution in Lanzhou was more severe than that in Jiayuguan and Jinchang from 2014 to 2017.The polluted days of PM_2.5 in Lanzhou?242 days?were almost 3-5 times that of Jiayuguan and Jinchang,and the polluted days of PM₁₀in Lanzhou?330 days?were obviously higher than those in Jiayuguan?225 days?and Jinchang?212 days?.The concentrations of particulate matter in the three cities were basically higher in spring and winter,but lower in summer and autumn.Due to the impact of sand and dust events,the daily average concentrations of PM₁₀ in Jiayuguan,Jinchang and Lanzhou fluctuated strongly and had large amplitudes,with the range of16-2280?g/m³,10-1789?g/m³ and 23-1398?g/m³,respectively.In terms of interannual changes,the annual average concentrations of particulate matter in Jiayuguan and Jinchang were generally lower than that in Lanzhou,and showed a downward trend,while the upward or downward trend was not obvious in Lanzhou.The concentrations of SO₂,NO₂ and CO were the highest in winter and the lowest in summer in the three cities during 2014-2017,while O₃ showed the opposite trend.The pollutions of CO in Jiayuguan,Jinchang and Lanzhou were relatively lighter,and the days exceeding the secondary standard were only 0,3 and 5 days,respectively.The annual average concentration of SO₂ in each city did not exceed the standard every year,and it showed a continuous downward trend.However,in comparison,the pollution of SO₂ was the most severe in Jinchang,and the polluted days were up to 28 days,while the other two cities were not over the standard.The average annual concentrations of NO₂ in Jiayuguan and Jinchang did not exceed the standard,and continued to decline,while that of the Lanzhou showed a continuous upward trend,exceeding the standard every year and significantly higher than that in Jiayuguan and Jinchang.The pollutions of SO₂ in Jinchang and NO₂ in Lanzhou were the most severe in January and December that were the months needed to be strictly controlled.The annual average concentration of O₃ in Jiayuguan was the highest every year,followed by Jinchang,and Lanzhou was the lowest.The annual average concentration of O₃ in Lanzhou showed a continuous upward trend,and there was no obvious sign of increase trend in the two cities of Hexi.The evaluation level of air quality of the three cities basically belonged to Class II?good?or higher in the evaluation level,but in comparsion,the air quality in Lanzhou was the worse,with the worst in winter and the second in spring.The air quality in Jiayuguan and Jinchang was the worst in spring,followed by summer?Jiayuguan?and winter?Jinchang?,but were generally at the level of grade I?excellent?.The main pollutants in Jiayuguan and Jinchang were PM₁₀,O₃ and PM_2.5 in turn.In addition,the impact of SO₂ on Jinchang cannot be underestimated.The main air pollutants in Lanzhou were PM₁₀,PM_2.5 in turn,and the pollution degree of O₃ and NO₂ were basically similar.The pollution of other pollutants was relatively lighter in the three cities.There were major transport pathways coming from three directions:the northwestern pathways?for Jinchang and Lanzhou?,the western pathways?for Jiayuguan and Lanzhou?,and the northern pathways?for Jiayuguan and Jinchang?.The corresponding potential dust sources for these pathways were the northwesterly sources?the Hexi region and Northern Xinjiang,including Turpan Basin and Gurbantunggut Desert?,the westerly sources?Kumtag Desert,Qaidam Basin?and the northerly sources?the deserts and Gobi in the central and western regions of Mongolia and western Inner Mongolia,including Badain Jaran Desert,Tengger Desert,Ulan Buh Desert,Kubuqi Desert?,respectively.In addition,the northern Tibetan Plateau was another important source affecting Jiayuguan.There were distinct differences among the regional transport contributions from various directions.The PM₁₀ concentrations?percentages?that exogenous dust sources contributed to Jiayuguan,Jinchang and Lanzhou decreased in a sequence from west to east at 47?g/m³?29.8%?,40?g/m³?27.1%?and 26?g/m³?17.3%?,respectively,which were attributed predominantly to the long-range transport of dust sources with the remainder coming from local or nearby emissions.The above decreasing tendency was in accordance with the distance effect from the dust sources to the receptor sites.