Composition Characteristics And Source Analysis Of Organic Components In PM_2.5 In Baoding City In Winter

As one of the important cities in the Beijing-Tianjin-Hebei region,Baoding City has many heavy pollution processes in winter.Particulate matter is the major pollution and the organic components in particulates account for a large proportion of its composition.Therefore,this study carried out PM_2.5 manual sampling at Baoding Reception Center（downtown）and Zhuozhou Vocational Education Center（county）from February 1st to March 10th,2019.DRI MODEL2001A and GC-MS were used to analyze the carbon components and organic components in the samples.Combining with online OC,EC data and meteorological data from state-controlled sites,using carbonaceous aerosol characteristic ratio method,PMF model,backward trajectory and potential source model to analyze the concentration changes of organic components in fine particles,and explore the main sources of changes in the concentration of organic components.To provide a scientific basis for the prevention and control of heavy air pollution in Baoding City in winter.The results show that:（1）During the sampling period,Baoding City experienced two heavy pollution,and the number of days when the air quality reached severe pollution or above was 9days in total.The average concentration of PM_2.5 in urban areas and districts and counties were 123.98±68.82μg/m³ and 108.68±53.62μg/m³,respectively.The average relative humidity reaches more than 50%,and the average wind speed is below 1.5 m/s.It is a state of high humidity and low wind and provides good conditions for the reaction and accumulation of pollutants.（2）During the sampling period,the concentration of OC and EC in the study area were 23.55±10.53μg/m³,3.90±2.17μg/m³ and 18.12±6.95μg/m^3,2.77±1.51μg/m³,respectively.The correlation of OC and EC is good,which indicates they have a certain degree of homology,and the OC/EC ratios of the downtown and county were 6.04 and6.54,respectively,that indicated the source of pollution in Baoding during the sampling period was mainly coal-burning emissions.In the pollution periods Z1 and Z2,the char-EC and soot-EC ratios of the downtown and county were 24.91,24.71,21.14,and 34.76,respectively,which further indicated that the carbon component in the sample was greatly affected by the combustion source.（3）The characteristic ratio method and PMF model were used to analyze the sources of organic components.The results showed that during the sampling period,the ratio ofρ（Flu）/ρ（Pyr）,ρ（Ant）/ρ（Ant+Phe）,andρ（Ba A）/ρ（Ba A+Chr）in PAHs in downtown and county were 1.18,0.25,0.40 and 1.29,0.30 and 0.32,respectively.The source of PAHs was mainly affected by the burning of coal and biomass.The highest sugar in samples from downtown and county were both levoglucan,their concentrations were 140.15 ng/m³ and 139.49 ng/m³,respectively.The L/M/ratio results indicated that the biomass combustion during the sampling period was dominated by hardwood combustion.The results of malonic acid/succinic acid and C₁₈/C₁₆ showed that the combustion source and the traffic source had a certain influence on the sampling site.The estimation of the SOC found that the secondary source accounts for 30-40%of the organic carbon,indicated that PAHs,sugars,organic acids and SOA precursors undergo more secondary conversion during the sampling period.The results of the PMF model show that during the sampling period,Baoding City was not only heavily affected by combustion sources,but also by pollution sources such as traffic sources and dust sources.（4）The analysis of backward trajectories and potential sources of airflows at different altitudes showed that the external transmission of Baoding’s atmosphere during the sampling period was mainly affected by the short-distance transmission of air masses from the south（40%-60%）and east（20%-40%）.The analysis of potential sources shows that at the heights of 10 m,50 m,and 100 m,the air pollution in Baoding City during the sampling period was mainly concentrated in the local area and its southern and eastern regions.At the height of 500m,Baoding City was more affected by external transmission.As the altitude increases,the influence of external transmission on the study area gradually becomes larger.