| With the economic development of the northeast region in recent years and the increase in environmental protection and remediation efforts,the previous haze-based pollution phenomenon is increasingly reduced,the concentration of particulate matter decreases year by year,but then comes the rise in ozone concentration and particulate matter together with the composite pollution,this change in pollution characteristics urgently requires the government to introduce a new round of pollution prevention and control plan,bring ozone into the key supervision scope and carry out coordinated control with particulate matter.In order to identify the sources of ozone pollution in Changchun and surrounding areas,source apportionment of ozone in Changchun and surrounding cities needs to be carried out.The spatial and temporal distribution of ozone in Changchun shows that the concentration is significantly higher in summer than in other seasons,the monthly average concentration is generally higher in May and July,and the daily variation trend is"single-peak",with the daily peak occurring from 15:00 to 16:00.The spatial distribution results show that the concentrations in suburban areas are generally greater than those in built-up areas,the concentration distribution in Nongan County is generally higher than that in other suburban areas,and the distribution trend in built-up areas is gradually increasing from the center of built-up areas to the periphery.In summer,the concentrations in all areas are generally higher than those in other seasons,ranging from 28 to 40μg/m~3 in built-up areas and 31 to 46μg/m~3 in suburban areas,while in winter,the concentrations in all areas are the lowest,ranging from 13 to 25μg/m~3 in built-up areas and 19 to 31μg/m~3 in suburban areas.The relatively high concentrations in built-up areas in all seasons are in Erdao District and Kuancheng District,while the suburbs are Nongan County and Shuangyang District.In this study,we use the WRF-CMAQ model,together with the Multi-resolution Emission Inventory for China（MEIC）developed by Tsinghua University,to first simulate ozone in Changchun and five surrounding cities in Spring（April）,Summer（July）,Autumn（October）,and Winter（January）of 2019,and also used the ISAM source apportionment module of the CMAQ model to analyze the ozone sources at two aspects and two scales:regional and industry,as well as year-round and four-season.The model evaluation results all indicate that the model fits well,and the correlation between WRF simulations and observations is generally greater than 0.7,and the correlation between CMAQ results is generally greater than 0.6,all of which pass the significance test.Ozone concentration is somewhat underestimated and wind speed is slightly overestimated in most of the time periods,resulting in high absolute values of NMB and NME.However,the time series of simulation results show that the model basically reproduces the daily ozone daily trend,and the simulation results are acceptable compared with previous studies of the same type.The ozone source apportionment results show seasonal differences,and the percentage of ozone concentration in Changchun 2019 is 61%by long-range transport outside the simulation domain,and 52%by long-range transport in summer,which is slightly lower than other seasons.The statistical results of intra-domain transmission in the simulation domain show that the total percentage influenced by cities in the simulation area is between 45%and 49%,and is more influenced by the transmission from Siping and Songyuan in the spring,autumn and winter seasons,while it is more influenced by Jilin and Siping in the summer.The spatial distribution results show that,excluding the influence of local sources,Changchun is dominated by the transmission in the northeast and northwest directions in spring and autumn,while the transmission directions are east and southwest in summer,as well as south and northwest directions in winter.The source apportionment results of each emission source show that industrial and traffic sources are the source sectors of ozone in Changchun,and both have the highest percentage of the four source sectors in summer,5.7%and 6.0%respectively,while the percentage of residential and power plant sources increases by 2.3%and 3.9%respectively in winter,which is related to the heating period in winter.The spatial distribution trend of the concentration contribution in spring,autumn and winter shows a gradual decrease from northeast to southwest,while in summer,the concentration contribution from northwest increases. |
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