| In order to fully grasp the trend of air pollution changes and the causes of heavy pollution processes in Baoding City in recent years,this study is based on online monitoring of atmospheric pollutants and particulate matter components in Baoding National Control Station from January 1,2013 to March 31,2019.In recent years,Baoding city's major atmospheric pollutant pollution characteristics and trends have been studied,and the regional transmission and potential source regions of air pollution affecting Baoding City have been analyzed to determine the dynamic changes of particulate matter components and potential sources of pollution during autumn and winter and during heavy pollution.Research indicates:?1?From 2013 to 2018,the air quality in Baoding City continued to improve,and the concentration of atmospheric pollutants continued to decrease.In 2018,the average annual PM2.5 concentration in Baoding City was 67?g/m3,a decrease of 20.2%compared with 2017;?g/m3 decreased by 68?g/m3,a decrease of 50.4%.The average concentration of??O3-8h?in 2018 was 193?g/m3,which was an increase of 70.80%compared with 2013.In summer,??O3-8h?rises year by year,and ozone pollution gradually becomes prominent;the type of pollution in autumn is more motorized;the type of pollution in winter shifts from the coal-burning type in 2013-2014 to the coal-burning type in 2015-2018 and incomplete combustion Mixed effects.In the spring of2018,Baoding City was mainly affected by the air masses in the three directions of south,northeast and northwest.The southern air mass from Handan-Xingtai-Shijiazhuang carried higher concentrations of pollutants;in summer,it was affected by the three directions of south,east and northwest.The air mass transmission is affected by the lowest concentration of pollutants in four seasons;the air mass in the two directions is affected by autumn.The air mass in the northwest and the south is similar,but the concentration of pollutants in the southern air mass is higher than that of the northwest air mass;The air masses in the northwest and east directions are affected.The transmission distance of the eastern air masses is shorter,which is greatly affected by the surroundings of Baoding.Concentration weight trajectory analysis?CWT?was used to analyze the potential source area of PM2.5 pollution in Baoding City.The potential source areas affecting PM2.5 in Baoding City were mainly distributed in Handan City,Xingtai City,Shijiazhuang City,and Hengshui City.?2?An analysis of autumn and winter in Baoding City found that the high cumulative concentrations of PM2.5 in autumn and winter in 2016,2017 and 2018accounted for a decrease of 5.56%,6.21%and 2.58%respectively in the same period of 2015,which was the largest decline rate among the six pollutants;followed by PM10;the decrease in SO2 and NO2 is smaller,indicating that the emergency measures have better peak-shaving effects on particulate matter during heavy pollution in Baoding than gaseous pollutants.In autumn and winter,the water-soluble ions in Baoding City mainly consist of secondary ions SNA(SO42-,NO3-,NH4+).The concentrations of SO42-,NO3-and NH4+are?12.15±15.76??g/m3 and?23.36±22.11??g/m3 and?11.38±10.65??g/m3,the SNA concentration accounts for 80.62%of the total water-soluble inorganic ion?WSI?concentration and 46.57%of the PM2.5 concentration.As the degree of pollution increases,the particulate matter becomes more acidic,Cl-plays a smaller and smaller role in the neutralization,and the pollution process tends to be more secondary.In autumn and winter,the mass concentration of total carbon?TC?in particulate matter in Baoding City accounted for 36%of PM2.5,indicating that Baoding City was polluted by carbonaceous aerosol to a certain extent,and organic carbon?OC?accounted for PM2.5 The ratio is 25%.Organic carbon?OC?and elemental carbon?EC?are found by correlation analysis,and they have good homology,mainly from coal combustion and biomass combustion.In autumn and winter,Baoding City has a secondary organic aerosol,but the secondary organic carbon?SOC?/organic carbon?OC?is 33%,which has a small impact.Air pollution in Baoding City in autumn and winter is mainly caused by the combined effects of coal-fired,industrial and motor vehicle emissions.?3?In the heavy pollution incident in the autumn and winter of 2018,the partial coal-fired pollution has increased compared with the autumn and winter season of 2017,indicating that coal combustion is still one of the sources of pollution that Baoding City needs to control.In the process of heavy pollution in autumn and winter,a typical secondary pollution process from January 10 to January 14,2019 is selected as the pollution period,and February 6 to February 10,2019 is the non-polluting period.For two different periods The dynamic analysis of the chemical composition of particulate matter.The concentration and proportion of SNA(SO42-,NO3-,NH4+)in the polluted period were higher than those in the non-polluted period.At the same time,the conversion of SO2 and other gaseous pollutants to SO42-and other PM2.5 secondary components during the pollution period is an important driving force for the rapid rise of?(PM2.5)in Baoding.At the same time,during this pollution process,stable weather conditions are conducive to the accumulation of acid ions and make the particulate matter more acidic.Principal component analysis explained that the main sources of this heavy pollution process are winter heating coal,industrial fossil fuel combustion,biomass combustion and road dust.Through backward trajectory and potential source analysis,in addition to the influence of county concentration in Baoding City,PM2.5potential source areas of Baoding City are mainly distributed in Shijiazhuang City,Shuozhou City,and Hengshui City. |
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