Analysis Of PM_2.5 Pollution Characteristics And Sources In Shenyang Based On CMAQ-ISAM Model

After entering the twentieth century,China’s urbanization and industrialization process has been accelerating,with the rapid development of the social economy,China’s air quality has continued to deteriorate,and a series of environmental problems have become prominent.Shenyang is the capital city of Liaoning Province,located in the southern part of Northeast China.It is a typical industrial city with a large industrial structure.PM_2.5is one of the main pollutants of air pollution in Shenyang.In 2020,the PM_2.5concentration in Liaoning Province was 39μg/m³,while that in Shenyang City was 42μg/m³.In order to further understand the pollution characteristics of PM_2.5in Shenyang,the WRF-ISAM model was used to analyze the source industries and source regions of PM_2.5in Shenyang.The temporal and spatial distribution characteristics of PM_2.5pollution in Shenyang show that the number of polluted days in Shenyang accounts for 59.5%of the total number of polluted days in the year,with PM_2.5as the primary pollutant.In2020,the hourly value of high PM_2.5pollution in Shenyang was concentrated in January,February,April,November and December,while the concentration was low in other months.The significant seasonal distribution of PM_2.5in Shenyang in 2020 is characterized by winter>spring>autumn>summer.The diurnal variation of PM_2.5concentration showed a"double-peak-double-valley"pattern,and the first valley value appeared at 4:00～6:00,and then the PM_2.5concentration increased.The first peak value appearing around 8:00～11:00,and then the concentration showed a downward trend.After reaching the trough at 17:00～18:00,the concentration gradually increased to the second high value area around 22:00,which was related to the changes of atmospheric conditions and human activities.The spatial distribution of PM_2.5shows that the dominant wind direction in the city was westerly in January,which resulted in heavy PM_2.5pollution in the eastern and northern parts of Shenyang,namely,the concentration of PM_2.5was high in the urban areas of Shenyang,Faku County,and Kangping County.In May,July and September,there is more precipitation and it is affected by wind direction and wind speed.The air movement in the troposphere is more intense than that in January,which is conducive to the diffusion of PM_2.5,so the PM_2.5concentration is lower.The simulation period of the WRF model and CMAQ model were all in January,May,July,and September 2020.Five indexes including correlation coefficients R,MFB,MFE,NMB and NME were selected to evaluate the performance of the simulation results of the model.The meteorological factors evaluated included temperature,wind speed and air pressure.The evaluation index of the WRF model shows that the correlation coefficient of temperature is between 0.84 and 0.91,the correlation coefficient of wind speed is between 0.52 and 0.73,and the correlation coefficient of air pressure is greater than 0.9.Except for wind speed in September,which had an MFE of slightly over 50%,the other factors all had MFB of-30%to30%and MFE of less than 50%.The evaluation index MFB of the CMAQ simulation results is between-30%～30%and MFE is less than 50%.Therefore,WRF and CMAQ models have good simulation performance and can be used for subsequent simulation analysis.The analysis results of PM_2.5source industries in Shenyang show that industrial sources,civil sources and transportation sources are the main contributing sources of PM_2.5concentration in Shenyang,and initial field sources,boundary sources and other unlabeled sources are also important sources of PM_2.5concentration,followed by power sources and agricultural sources.The contribution of PM_2.5from civilian sources varied greatly,with the lowest contribution rate in September and more than25%in other months.Shenyang urban civil sources and transportation sources discharge more,and the eastern industrial park PM_2.5pollution is heavier.The eastern Shenbei New Area is a state-level economic and technological development zone in the Shenzhen-West Industrial Corridor near Shenyang,located in the middle of the Northeast Urban Corridor.There is a dense traffic network here,with Beijing-Harbin Expressway,National Highway 101,National Highway 102 and National Highway203 running through the whole area,leading to significant emissions of traffic sources and civil sources in the northern Shenyang New Area.The high value of PM_2.5pollution is concentrated at the junction of Shenyang and other cities.Therefore,regional joint prevention and control of air pollution are crucial for the air pollution control of Shenyang and its surrounding cities.The regional contribution of PM_2.5sources in Shenyang shows that the local contribution varies little in different months,and the highest contribution rate is16.99%in January.The contribution rate was the lowest in July at 10.16%.The PM_2.5contribution rate of Shenyang’s surrounding sources varied greatly in different months,with the lowest contribution of 16.69%in July.In January,the contribution rate of peripheral sources was the highest,55.01%.The long-distance transmission was the main regional source of PM_2.5in Shenyang in May and July.The regional transmission contribution between cities shows that local emission is the main source of PM_2.5concentration contribution in each city.Besides the local contribution,PM_2.5concentration in Shenyang is greatly influenced by Tieling City’s transmission contribution,and Liaoyang City’s transmission contribution is also relatively large in January and September.In addition,the transmission between other cities varies greatly,and in different months,the transmission between cities also presents different characteristics.