Study On Source Apportionment And Control Countermeasures Of PM_2.5 In "2+26" Cities During The Heating Season

PM_2.5 is one of the primary pollutants in many cities in China.The emission intensity of pollutants in“2+26”cities in Beijing-Tianjin-Hebei region and its surrounding areas is far higher than the national average.During the winter heating season,PM_2.5 pollution is serious,and the interaction between cities is significant.It is of great significance to carry out research on the characteristics and source apportionment of PM_2.5 components in this region for in-depth understanding of the causes of pollution,fine treatment of air pollution and coordinated control among cities.This paper takes“2+26”cities in Beijing-Tianjin-Hebei region and its surrounding areas as the research area,study time is on November 1,2016 to March31,2017,during the heating period,the observation data were used to analyze the concentration and components characteristics of PM_2.5,the CAMx-PSAT model was used to analyze the source apportionment of PM_2.5 and its main components in the heating season and three pollution episodes with different degrees during December16-23,2016,February 1-7,2017 and March 2-6,2017.Different emission reduction schemes are designed for three pollution episodes and the numerical simulation and effect evaluation are carried out with the model,combined with the above research,“2+26”cities pollution control countermeasures are also proposed.The main research results are as follows:Firstly,the concentration and component characteristics of PM_2.5 during the heating season were studied based on the observation data.Through the analysis of PM_2.5 concentration data,it is found that the average number of pollution days are97 days,accounting for 64.36%.The average PM_2.5 concentration of all the cities exceeded 75?g/m³ during the heating season,the maximum hourly concentrations of all cities exceeded 350?g/m³ and even reached 816?g/m³ in Handan,the overall pollution is serious.The components with the highest content of PM_2.5 are OC,NO₃^-,SO₄^2-,NH₄⁺and EC,with an average proportion of 19.27±2.67%,17.06±1.86%,14.31±1.46%,9.94±0.71%and 2.65±0.41%,respectively.The average proportion of undetermined components such as water and insoluble substances is 25.85±2.16%.In the pollution period,except the EC proportion decreased by 0.20%,the proportion of other four major components and undetermined components increased by 0.11%,1.14%,2.51%,0.41%and 1.61%,respectively.The remaining less abundant components accounted for more than 10%of the total,among them,elements Mg,Ca,Ba,Ti,V,Fe,Al,Sc,P and Si are mainly from the crust,elements Na,K,F,Cr,Mn,Co and Ni are both from anthropogenic natural sources,while elements Cl,Cd,Sn,Cu,Zn,As,Se,Pb and S are mainly from anthropogenic emissions.Secondly,the source apportionment study of PM_2.5 and its major components was carried out by using the CAMx-PSAT model during the heating season and pollution episodes.The contribution of local PM_2.5 emissions in“2+26”cities is 13%-52%,that of non-local emission is 16%-63%,and that of peripheral regions outside“2+26”cities is 14%-50%.Local emissions contribute the most to PM_2.5 of Shijiazhuang and Tangshan,nonlocal emissions contribute the most to cities like Beijing,Tianjin and Hengshui,peripheral emissions contribute the most to cities like Taiyuan,Zibo and Jining.In the case of heavy pollution the local contribution of each city tends to decrease,the interaction within“2+26”cities is more significant.The contribution of residential,industrial,agricultural,transportation and power sources to PM_2.5 is 41.38%±5.93%,30.50%±5.20%,9.62%±0.85%,9.59%±1.69%and 6.15%±1.46%,respectively.SO4^2-is mainly from industrial and residential sources,with an average contribution of 45.46%±5.71%and 41.14%±6.25%,respectively;the contributions of industrial sources to NO3^-are 35.20%±1.88%,transportation sources 23.23%±3.23%,power sources 15.06%±1.68%,and civil sources 14.05%±2.87%;NH₄⁺is mainly contributed by agricultural sources,accounting for 86.40%±4.63%;EC comes from residential,industrial and transportation sources,with an average contribution of 54.66%±5.75%,26.76%±6.55%and 18.50%±3.96%,respectively;OC is mainly contributed by residential sources,accounting for 81.07%±5.75%;the other components are mainly from industrial and residential sources,with an average contribution of 43.13%±6.72%and45.04%±7.05%,respectively.Except for NO₃^-,the regional contribution of other PM_2.5 components is close,the local contribution of NO₃^-is 4%-26%,significantly lower than that of other major components.During the three pollution episodes,December 16-23,2016,February 1-7,2017 and March 2-6,2017,the average maximum daily concentration of PM_2.5 in“2+26”cities is 367?g/m³,197?g/m³ and112?g/m³,respectively.The study area as a whole achieved severe,serious and mild pollution levels.The relative contribution ratio of PM_2.5 sectoral sources in the three pollution cases is relatively consistent,all of which are residential sources>industrial sources>agricultural sources and transportation sources>power sources,agricultural sources and transportation sources contribute roughly the same amount.The residential sources contributed the most and were 2.76%,8.20%and 6.21%higher than the average level of heating season.The contribution of local sources is24.82%±9.27%,26.68%±10.29%and 30.87%±9.04%,respectively.With the aggravation of pollution,the local contribution of PM_2.5 in most cities decreased,and the interregional interaction is even more pronounced.Finally,different control schemes were designed for three PM_2.5 pollution cases,the results of PM_2.5 concentration improvement after adopting control measures were analyzed,and suggestions for pollution control countermeasures were put forward.The simulation results showed that the average PM_2.5concentration of the three pollution cases decreased by 38.19%±9.26%,36.84%±5.97%and 11.88%±3.07%respectively.In case 1 and case 2,the overall pollution level decreased by 1 level,in case 3,the PM_2.5 concentration decreased but the overall pollution level did not change.This suggests that for mild PM_2.5 pollution,more stringent control measures are needed to achieve the goal of reducing pollution level.Beijing,Tianjin and cities of Hebei and Henan provinces in“2+26”cities is prone to accumulation of pollutants and the emission intensity of pollutants is significantly higher than that of other regions,so it should be the key area for pollution control.With the increase of PM_2.5 concentration,the local contribution tends to decrease,and the interregional interaction is even more pronounced.Only by adopting inter-city joint prevention and control,and taking more precise control measures for key region and sectoral sources,can the ideal effect be achieved.Residential and industrial sources contribute the most,and the concentration of PM_2.5 can be effectively reduced by focusing on controlling these two sources.Based on the analysis of observation data,this paper reveals the concentration and component characteristics of PM_2.5 during the“2+26”cities heating season.The CAMx-PSAT model was used to quantify the source contribution of PM_2.5 and its major components during the heating season and pollution episodes.The PM_2.5pollution control scheme was designed,the results of PM_2.5 concentration improvement after adopting control measures were evaluated and analyzed,and suggestions for pollution control countermeasures were put forward.The results of this study can provide certain reference for the control of PM_2.5 pollution in“2+26”cities in Beijing-Tianjin-Hebei region and its surrounding areas.