The Change Of Air Pollution Characteristics In Recent Years In Handan, China

In this study we collected the major air pollutants data from the National Control Site of Hebei Province from 2013 to 2017 to analyze the interannual and seasonal variations of conventional pollutants in Hebei Province.Using the chemical composition data of the offline sampling of PM_2.5 in Bengbu City in 2013 and 2017,the chemical composition changes in the atmosphere in Bengbu City from 2013 to 2017 were analyzed.Finally,the WRF-Chem model was used to calculate the surrounding cities according to the scenario simulation method.The main conclusions are as follows:（1）In addition to ozone,the pollutants in the city of Hebei Province showed a downward trend.In 2017,the concentration of PM_2.5 in Chengde and Zhangjiakou has reached the national two.The standard is 35μg·m^-3.The SO₂ concentrations in all cities of Hebei Province have reached the national secondary standard（60μg·m-3）.The effect of NO₂ improvement was not as obvious as that of SO₂.The concentrations of Hengshui,Chengde,Zhangjiakou and Qinhuangdao reached the national secondary standard(40μg·m^-3).The concentration of O₃ is on the rise in the past three years,and the pollution is gradually increasing.（2）In addition to Zhangjiakou and Chengde in Hebei Province,the PM_2.5 concentrations in other cities have obvious seasonal variations.That is,the winter concentration is the highest,the fall is second,the spring is better,the summer is the lightest,and the overall trend is downward.The seasonal concentration change of O₃ is the highest in summer.As far as the over-standard rate is concerned,except for O₃,the seasonal variation characteristics of the over-standard rate of each city are obvious,the highest rate exceeds the standard in winter,the second in autumn,the third in spring,and the lowest in summer.（3）The total chemical composition of Handan City showed a downward trend from 2013 to2017,and SO₄^2-,NO₃^-and NH₄⁺decreased most significantly.The decrease rates of OC and EC were 9.4%and 37.1%respectively.The seasonal variation of chemical components in PM_2.5 is higher in autumn and winter than in spring and summer.By comparing NOR with SOR,NOR in2013 was greater than SOR,indicating that the conversion of gaseous NO₂ to NO₃^-was more intense in Handan than that of SO₂ to granular SO₄^2-in most of the time,and the conversion rate in2017 was opposite to that in 2013.SOC/OC in 2017 was lower than that in 2013,and POC was higher than that in 2013,indicating that the secondary organic pollution in Handan City in 2017was reduced.Comparing the ratio of NO₃^-/SO₄^2-,In 2017,the ratio of NO₃^-/SO₄^2-increased significantly,all above 1,indicating that the impact of mobile sources was gradually increasing.（4）According to the analysis of the sources of pollutants in Handan,the main source of winter pollution in Handan is the local and short-term transport with surrounding Xingtai,Shijiazhuang and other cities,and the contribution rate of the surrounding transmission has increased.As far as the contribution rate of surrounding cities to Handan’s air pollution is concerned,In Hebei Province,the contribution rate of emissions（including Handan local）to Handan is 60.5%.The local emissions contribution rate to Handan is 46.2%.The contribution rate of central and southern cities（Shijiazhuang,Langfang,Baoding,Hengshui,Xingtai）to Handan is12.4%.The contribution rate of other surrounding cities to Handan is all the same.Less than 5%.