Response Of PM_2.5 Concentration To Emission Reduction Of Its Precursors In Winter In China

With the accelerating process of industrialization and urbanization in the past few decades,the emission of pollutants in China has increased significantly,and the problem of air pollution has become increasingly serious.Winter haze is a severe problem in China,which could be caused by anthropogenic pollutant emissions,meteorological and topographical factors.In recent years,the main cause of haze is fine particulate matter(PM_2.5).Particulate pollution has become a frequent air pollution problem in most cities and regions in China.PM_2.5 has caused serious impacts on climate change and people’s health,which has attracted widespread attention from all walks of life.High PM_2.5 concentrations will reduce atmospheric visibility,causing negative effects on air quality and ecosystem.At the same time,toxic and harmful substances such as organics and heavy metals can adsorb on the surface of PM_2.5.Then,these substances will increase the incidence of respiratory diseases,cardiovascular diseases and chronic bronchitis,resulting in the increase of the mortality rate.Given the severe situation of air pollution in China,it is urgent to prevent and control PM_2.5 pollution.The most direct method is to reduce the emission of anthropogenic pollutants.In this paper,WRF-Chem（Weather Research and Forecast Model with Chemistry）model was used to simulate the concentration and spatial distribution of PM_2.5,its components and precursors from 2 to 30 2016 January in China.And the sensitivity of PM_2.5 mass concentration to emission reduction of different kinds and proportions of precursors was also be researched and compared in this model.Since 2013,Chinese governments at all levels have imposed strict limits on PM,SO₂ and NO_X emissions.Most regions have seen a significant reduction in PM_2.5 pollution.However,the results of this study show that PM_2.5 pollution still exists.China’s PM_2.5 concentration still exceeds the World Health Organization’s Phase 2 transitional target of 25μg/m³,and most areas in the heavily polluted winter do not even meet China’s second-level PM_2.5 concentration standard.Due to the dense population and rapid economic development,the areas with the worst PM_2.5 pollution are usually concentrated in the Beijing-Tianjin-Hebei region,the Yangtze River Delta,Sichuan and Chongqing regions,Shandong,Henan,Hunan and Hubei provinces.In addition,PM_2.5 concentrations in winter are higher in southern China than in northern.Not only that,as an important component of PM_2.5,the concentration and distribution of secondary inorganic aerosols are similar to that of PM_2.5.The concentration of secondary inorganic aerosol in southern China was significantly higher than that in northern China.The concentration of secondary inorganic aerosol in Sichuan-Chongqing urban agglomeration was the highest,followed by Guizhou,Hunan,Guangxi,Guangdong and Hubei.The general rule is that with the decrease of latitude,the percentage of PM_2.5 accounted for by secondary inorganic aerosols increases gradually.Therefore,the secondary inorganic aerosol occupied a significant position in PM_2.5.The spatial distribution of secondary inorganic aerosol had a strong correlation with that of NH₃,SO₂ and NO_X.PM_2.5 had uneven sensitivity to the precursors induced by anthropogenic emissions,ranging from strong to weak relationships for NO_X,NH₃ and SO₂.NO_X,which has the most obvious benefits,was chosen for further emission reduction simulation.In the scenario of reducing NO_X,the degree of PM_2.5 concentration reduction was more obvious in the south than that in the north.Therefore,the northern region with less secondary inorganic aerosol content in PM_2.5 can combine with other emission reduction measures.In the southern region,the Sichuan-Chongqing urban agglomeration had the largest response,where the PM_2.5concentration decreased obviously.In addition,there was nonlinear relationship between the reduction of PM_2.5 concentration and the reduction of NO_X emission.The more NO_X emission reduction,the faster decrease in the PM_2.5 concentration.That can lead to increase in the benefit of quantitative targets.Therefore,air pollution control measures are particularly effective when the intensity become relatively strong.The results further confirmed that NO_X control played an important role in the control of PM_2.5 pollution.