Observation And Extinction Characteristics Of PM_2.5 In Typical Urban Areas Of North China

In the process of economic construction,China has continuously promoted industrialization and urbanization,which has led to an increase in energy consumption and the problem of atmospheric pollution has become increasingly prominent.As one of the three major economic circles in China,Beijing-Tianjin-Hebei,the increase in energy consumption and motor vehicle holdings has arouse serious air pollution problems,which are manifested by increased concentrations of atmospheric fine particles and frequent regional heavy pollution incidents.The concentration of particles in the atmosphere,chemical composition,and optical properties have different degrees of influence on radiation,extinction,and human health.Realizing the networked observation of regional PM_2.5.5 and studying its main physical and chemical characteristics will help to further explore the weakening of visibility by atmospheric particles.In this study,the mass concentration,chemical composition,and optical properties of aerosols in Beijing-Tianjin-Hebei region?Beijing,Shijiazhuang,Baoding,Tianjin,Tangshan,Xinglong,Xianghe?,and their correlation with each other,and the proportion of extinction of different components were analyzed by using fine particle sampling to elucidate the chemical composition versus optical properties.The impact of this study provides a scientific reference for the control of air pollution.The main findings are as follows:In the autumn and winter,the water-soluble ions of Beijing-Tianjin-Hebei were mainly secondary ions SO₄^2-,NO₃^-,and NH₄⁺,accounting for 66.9-84.2%of the total ion concentration.The ratio of NO₃^-/SO₄^2-is greater than 1.0 in autumn,and it is less than 1 in Shijiazhuang,Baoding and Tangshan in winter,indicating that motor vehicle emissions contribute more to pollution.The average concentration of Organic Carbon?OC?in PM_2.5.5 was between 4.7 and 80.1?g m^-3,and the urban stations and suburban stations were much higher than the regional background stations.The OC/EC ratios at various stations in winter were significantly higher than those at autumn,and the higher the OC and Elemental Carbon?EC?average concentrations,the higher the OC/EC ratio.The OC classification results showed that each site in autumn reflected the characteristics of burning straw.Using the IMPROVE equation to calculate the extinction coefficient of five sites in the Beijing-Tianjin-Hebei area during the autumn and winter of 2016,it was found that as the pollution gets worse,the proportion of extinction of sulfate and nitrate increases,and the extinction effect of fine soil decreases,and the fine soil become the most extinction component of the specific gravity when cleaning.The extinction effect of Coarse Mass?CM?is the weakest,and the change is not significant.Except for the extinction of fine soil in autumn of Tangshan and Tianjin,the main extinction substances in Beijing,Tianjin,and Shijiazhuang in the autumn are ammonium nitrate,extinction contributes 25.6%to 32.2%of the total calculated components.The visibility in winter is mainly affected by SNA?ammonium-sulfate-nitrate?and OM?organic matter?,the relative contribution rate of SNA extinction ability is as high as35.8%⁴6.7%.Tocontrolthecurrentatmosphericpollutioninthe Beijing-Tianjin-Hebei region in autumn and winter,and to improve atmospheric visibility,it is necessary to vigorously control the emission of organics and gaseous precursors such as NO_x and SO₂ from coal-fired and automobile exhaust to reduce the SNA and OM concentrations in aerosols.