Study On The Characteristics Of Temporal And Spatial Changes Of PM_2.5in China In 2015 And Sources And Health Risks

In 2015,the China Air Quality Monitoring Network achieved the coverage of all cities in the country for the first time.In order to better understand the distribution and origin of China's PM_2.5,this paper is based on the six types of air pollutant data(PM_2.5,PM₁₀,CO,NO₂,O₃,SO₂)released by China National Environmental Monitoring Center about1494 monitoring stations.Using a variety of statistical methods for data analysis of the spatial and temporal distribution analysis,and performs a correlation model using analytical sources.In order to reveal the possible health risks of PM_2.5 in China,this article collected the concentration values of PAHs and carcinogenic heavy metals in PM_2.5 published in the publicly-published literature from 2011 to 2016 through literature surveys to analyze and assess the health risks resulting conclusion as below:?1?The pollution situation of PM_2.5 in 2015 is still severe in China.From an annual average,only 20%of the cities have met the“Environmental Air Quality Standard”?GB 3095-2012?stipulated in the standard second class?35?g m^-3?.Two cities met the standard level?15?g m^-3?and no city reached the"Air Quality Standard"promulgated by the World Health Organization?WTO?in 2005?10?g m^-3?.From the point of view of the average annual distribution of PM_2.5,the urban clusters in the vicinity of the Taklamakan Desert and north of the Yangtze River are the two areas with the most severe PM_2.5 pollution.?2?In order to find China's"hard-hit area"of PM_2.5 pollution,according to the annual mean value of PM_2.5,Chinese cities were classified using the hierarchjcal cluster method.The results showed that the 35 cities which were located in the North China Plain?including Jing-Jin-Ji,Shandong Province and the northern part of Henan Province?belong to the same category and all have higher PM_2.5 annual averages.Through comparison with satellite data?an annual average aerosol map of MYD08_M3 data from MODIS C6 aerosol products?,the ground observations are in good agreement with the satellite observations.The North China Plain and the Northwestern Taklamakan Desert are the most serious pollution areas.At the same time,satellite observations also show that the concentration of aerosols in the Pearl River Delta region is relatively high,which is inconsistent with the ground monitoring results.In the results of spatial autocorrelation analysis,the high-concentration area starts from the Yanshan Mountains in the north,the Taihang Mountains and the Qinling Mountains in the west,the Yangtze River in the south,and the Yellow Sea and the East China Sea in the east.This area is the impact plain formed by China's two longest rivers?Yellow River and Yangtze River?.The results of various analytical methods all indicate that the North China Plain area is the"hard-hit area"of China's PM_2.5 pollution.?3?The temporal distribution characteristics of 35 PM_2.5 polluted cities obtained by hierarchjcal cluster method were analyzed,and the monthly averages were further clustered.The results showed that the pollution of PM_2.5 in these cities had a very significant time distribution feature.The months of heavy pollution tend to be the central heating season in the north,while in the non-heat season,PM_2.5 pollution tends to be lighter.This shows that atmospheric PM_2.5 pollution in the North China Plain should be closely related to heating activities in this area.?4?The PMF model was used to analyze the characteristics of air pollution in the highest value areas,which were mainly divided into three factors,photochemical secondary pollutants mainly O₃,combustion pollutants and particulate aerosol pollutants.In summer,the photochemical secondary pollutants are the main factors,and in winter,the combustion pollutants and particulate aerosols are the major pollutants,and the contribution rate of particulate aerosol pollutants is greater.?5?The correlation analysis among the pollutants in 35 polluted cities showed that:1)PM_2.5 has a good correlation with CO concentration,and this feature is more obvious in heavy pollution period?R>0.9156?;2)The correlation between PM_2.5 and NO₂ is significantly better than that of SO₂,and this law is even more pronounced during periods of heavy pollution.This status quo shows that with the promotion of SO₂ emission control measures,the type of air pollution in North China has changed from the traditional coal-fired pollution type to the mixed pollution of coal-fired vehicles.At the same time,NO₂ plays an important role in the formation of PM_2.5.?6?PSCF results show that the PM_2.5 concentration in the North China Plain is greatly affected by the origin of the air mass.During the heating period,the air mass basically comes from the inland areas of Inner Mongolia,Hebei,Shandong,Henan,and Anhui which are potential sources of pollution.The air masses during the non-heating period come from the south and coastal areas of the Yellow Sea.In December,where the pollution was most serious,the North China Plain was hardly affected by foreign atmospheric air masses,which also indicated that unfavorable weather conditions were another cause of the higher atmospheric PM_2.5concentration in the North China Plain in December.?7?The order of carcinogenic heavy metal concentrations from high to low was:Pb>Cr>As>Ni>Se>Cd>Co>Be.Pb has a high cumulative value in all cities;the health risk assessment results from PM_2.5 exposure show that:1)through the risk assessment for the intake of heavy metals and polycyclic aromatic hydrocarbons,it was found that the urban population in the north was exposed to PM_2.5.The health risks are much higher than those in the southern cities;2)The highest carcinogenic risk values for PAHs and carcinogenic heavy metals in most cities exceed the prescribed threshold of 1.0?10^-6,indicating that exposure to PM_2.5 has significant cancer risk.3)Cr and As are the carcinogenic elements with the highest health risk.