Analysis On The Causes Of Atmospheric Pm_2.5 Pollution In Xingtai During Autumn And Winter And Research On Control Measures

In recent years,there have been frequent regional and large-scale heavy pollution incidents of particulate matter,especially atmospheric fine particulate matter(PM_2.5),especially in northern cities.Xingtai City is one of the air pollution transmission channels in the Beijing-Tianjin-Hebei region.Heavy pollution occurs frequently in autumn and winter,and the air pollution problem is severe.Therefore,this study took Xingtai City as the research area,carried out intensified observations in autumn and winter,analyze particle concentration and chemical composition,and combined with the online data of conventional pollutants to discuss and study the air quality characteristics,PM_2.5concentration changes and composition of Xingtai City.It is divided into components and comprehensively uses the chemical mass balance model（CMB）and positive matrix factor model（PMF）to identify the key sources of PM_2.5 in Xingtai City;at the same time,through the analysis of typical heavy pollution incidents,analyze the characteristics and causes of heavy pollution,in order to formulate targeted The scientific and scientific air pollution control countermeasures provide the necessary scientific basis.The main conclusions are as follows:（1）The air quality in Xingtai City has been improving year by year,and various pollutants have dropped significantly,especially SO₂（74.7%）,but the concentration level of particulate matter is still high,and the over-standard situation is significant,especially PM_2.5,and the phenomenon of exceeding the standard in autumn and winter is still not ignored.（2）During the observation period,the average concentration of PM_2.5 in Xingtai City was112.9μg/m³,which exceeded 2.22 times of the secondary standard of"Ambient Air Quality Standard"（GB3095-2012）,the highest concentration reached 339.4μg/m³,and the maximum exceeding multiple was 8.7.The PM_2.5concentration is at a relatively high level;the spatial distribution is Shahe City>Neiqiu>Xingtai No.1 Middle School.（3）The PM_2.5 component analysis results during the observation period showed that the secondary components,organic matter and crustal elements accounted for a relatively high proportion,and the OM and nitrate concentrations increased significantly during the pollution aggravation stage.（1）Water-soluble ions:PM_2.5 is dominated by secondary components,and the concentration of secondary ions will increase significantly under severe and above polluted weather.The secondary ions NO₃^-,SO₄^2-,and NH₄⁺account for a high concentration,and the three account for more than 80%of the total water-soluble ions,and there is a significant upward trend with the increase of PM_2.5 concentration.Secondary ions under severely polluted weather levels and above The concentration is significantly higher than that on a clean day.（2）Carbon component:The average concentration of OC and EC are 19.03 and 7.39μg/m³,respectively.The concentration is the highest in January and the lowest in October.The concentration level in the heating season is twice higher than that in the non-heating season;the variation range of OC/EC is Between 2-3,the average ratio is 2.76,which preliminarily indicates that OC and EC in PM_2.5 in Xingtai City may be jointly affected by motor vehicle exhaust and coal-burning emissions;during the sampling period,the SOC concentration varies in the range of 0.01-38.17μg/m³,with an average The concentration is 8.02μg/m³,which accounts for about 41.3%of OC;the SOC concentration level in autumn and winter is significantly different,and the concentration level in winter is significantly higher than that in autumn.（3）Inorganic elements:The average concentrations of Si,Ca,Fe,K,Na,Al,Mg,Ti,and Zn are 3.55,1.56,1.41,1.72,0.89,1.42,0.19,0.14,and 0.07μg/m³,respectively.（4）PM_2.5concentration reconstruction results show that OM and nitrate are the most important chemical components in PM_2.5,accounting for 26.9%and 17.7%respectively,followed by crustal material（12.3%）sulfate（8.5%）and Ammonium salt（8.1%）has significant secondary pollution characteristics.（4）The analysis results of PM_2.5 sources show that the main contributing sources of PM_2.5in Xingtai City are coal-fired sources,secondary sources,dust sources and motor vehicle sources.（1）From the perspective of regional transmission,the simulation results based on the backward airflow trajectory model（Hysplit）show that the short-distance transport air masses in some cities in the southern province and surrounding cities outside the province have a greater impact on the concentration of pollutants in Xingtai City while the air masses from the north correspond to relatively low levels of particulate matter.The impact is relatively small.（2）The PM_2.5 source analysis results show that the results of CMB and PMF are relatively consistent.During the observation period,the main sources of PM_2.5 were coal soot,fugitive dust,nitrates and secondary.In the CMB results,the contribution of various pollution sources is coal soot（26%）>nitrate（19%）=fugitive dust（19%）>sulfate（9%）>motor vehicle（10%）=SOC（10%）>Others（5%）>Metallurgical dust（2%）.The analysis results of PMF method show that the contribution of the category sources is coal-fired source（28.1%）>secondary source（21.5%）>dust source（19.7%）>motor vehicle source（15.0%）>biomass combustion（9.8%）>industrial source（5.9%）.To sum up,although the ambient air quality in Xingtai City is improving year by year,the concentration of main pollutants is still high,and the phenomenon of exceeding the standard is significant.Air pollution is mainly caused by the combined effect of internal and external factors.The heavy pollution process in autumn and winter is dominated by secondary pollution,followed by the impact of dust and motor vehicles.Therefore,it is necessary to carry out strict management and control from the emission of precursors.The main control sources are coal-burning sources,dust sources,motor vehicle exhaust gas and industrial sources,etc.,and strict control is carried out.The focus of control includes deepening control of industrial industries and total coal Measures such as control,civil bulk coal combustion control,"vehicle oil road"overall management,and comprehensive dust control measures.