Simulation Study On Impact Of "2+26" Residential Coal Combustion On PM_2.5 In Beijing During Autumn And Winter

In the consumption structure of rural living energy in northern China,in addition to straw and firewood,civil bulk coal is an important part.In order to promote the adjustment of rural energy structure and improve the air quality of Beijing-Tianjin-Hebei region,especially with the acceleration of the clean transformation of rural heating in winter,such as"coal to electricity"and"coal to gas"in Beijing in recent years,The problems of environment and health caused by the combustion of household coal in rural areas in northern autumn and winter heating season have been effectively solved.In order to evaluate the improvement of PM_2.5 pollution and sulfate concentration in this region,especially in autumn and winter of Beijing,the air quality model was used to simulate the five heavy pollution events in autumn and winter of 2018-2019 in Beijing,and the results indicated that the high concentration area of PM_2.5 in"2+26"city is located in the western part of Hebei Province and southwest of Shandong Province,and it’s distributed in the north-south direction scattered or sheet.The simulation results of the combustion control scenario show that the maximum pollution concentration of PM_2.5 in the region is 324μg/m³ then reduced to 251μg/m³,the drop rate is 23%,while the PM_2.5 concentration in Beijing down to 124μg/m³,the decrease rate is 11%,which indicates that the alternative measures of civil coal make the heavy pollution weather in the area be effectively controlled;Sulfate is an important component of PM_2.5,SO₂ produced by rural residents’coal emission has a significant impact on the sulfate concentration in Beijing.The results show that the distribution of sulfate is similar to that of PM_2.5 in the basic scenario.The sulfate is distributed as the form of point,and high in the south while low in the north,indicating that the sulfate have a great contribution to PM_2.5.With the significant decrease of SO₂ concentration in the simulated area,the sulfate concentration has been improved greatly in each city,and the maximum sulfate concentration decreased by 4.70μg/m³ in the region,the drop ratio is 9%,while the sulfate concentration decreased by 4.68μg/m³ in Beijing,the drop ratio 24%.The influence and contribution of sulfate concentration in Beijing under control scenarios,such as transport,diffusion,aerosol chemistry and emission are further discussed.The results show that the formation of sulfate was significantly affected by physical process in the five heavy pollution cases in Beijing,horizontal advection and vertical diffusion are the main processes that affect the sulfate concentration in Beijing,but the contribution of horizontal advection process with different heavy pollution is different.After control,the physical process leading to sulfate formation remained unchanged but the intensity decreased in Beijing,and the contribution of concentration in vertical diffusion removal process decreased 34%,while that of aerosol secondary conversion decreased by 25%.However,the proportion of horizontal advection in the total absolute values of the four physical processes has increased significantly,with an average increase of 7%,indicating that the formation of sulfate is affected by external transport,and the absolute importance of the influence increased in Beijing.In order to explore the regional and industrial contribution and influence of SO₂and sulfate concentration formation in the target cities in Beijing-Tianjin-Hebei,combined with ISAM particle source tracing technology of air quality model,the article analyzes the source of SO₂,sulfate in the five heavy pollution processes in autumn and winter.The analysis of SO₂ source indicated that the contribution of civil sources has decreased significantly when the source category is considered under the control scenario,and the SO₂ concentration was mainly affected by industrial process sources（65%）in Beijing,indicating that the control of bulk coal has achieved results,and industry is the key department in Beijing and surrounding cities.The analysis of regional sources indicated that SO₂ mainly contributed from the nonlocal,accounting for 55%in Beijing.Hebei Province contributed 43%to Beijing on average,8 cities in Hebei Province played an important role in the formation of sulfate in Beijing,of which Baoding contributed 19%;The analysis of sulfate sources showed that the sulfate concentration is mainly affected by industrial process sources（82%）,and the regional sources analysis results showed that the sulfate was mainly contributed from the nonlocal in Beijing,which was consistent with the process analysis results.Hebei Province has the largest contribution in the nonlocal contribution,with an average contribution of 56%.The largest contribution of 8 cities in Hebei Province was Baoding,with an average contribution of 17%.It is suggested that Beijing should pay more attention to the emission control of pollution sources in its surrounding cities.