| Carbonaceous aerosols are an important component of PM2.5,which have a great influence on the formation of haze,regional climate,and human health.Therefore,it is important to study the pollution characteristics and sources of carbonaceous aerosols for the effective control of regional and urban carbonaceous aerosols.PM2.5 samples in the winter(2017 and 2018)and the summer(2018)and typical emission source particulate matter samples(coal-combustion dust,gasoline vehicle exhaust dust,diesel vehicle exhaust dust,biomass-burning dust,and dust)were collected in Changzhi,and the carbonaceous components(organic carbon-OC and elemental carbon-EC),carbon isotope(δ13C)composition and water-soluble ions were analyzed by thermal/optical carbon analyzer,isotope mass spectrometry and ion chromatography system,respectively.The sources of carbonaceous aerosol in PM2.5 were analyzed by the Positive matrix factorization analysis(PMF)and isotope mixing model,respectively,and compared and validated the results of the two methods.The primary conclusions derived from this research have been:1.During the sampling period,the average concentrations of PM2.5,OC and EC in Changzhi were 63.8±25.6,8.7±3.6 and 3.6±2.3μg/m3,respectively,with consistent seasonal variations of PM2.5,OC and EC,which all showed a seasonal variation of 2017 winter(75.6,12.5,and 6.0μg/m3)>2018 winter(57.8,6.2,and 2.1μg/m3)>2018 summer(47.5,5.6,and 1.4μg/m3).The secondary organic carbon(SOC)concentrations in 2017 winter,2018 summer and 2018 winter were estimated by the minimum correlation coefficient method,which was 6.9±2.8,3.7±1.2 and 3.2±1.4μg/m3,respectively,accounting for 56%,66%and 50%of OC concentrations.2.The source apportionment results of carbonaceous aerosol in PM2.5 in Changzhi were analyzed using the PMF receptor model,which showed that:the main sources of carbonaceous aerosol in 2017 winter were motor vehicle exhaust(42.3%),coal-combustion(32.0%),dust(12.9%),biomass-burning(8.4%),and secondary sources(4.5%).The ranking of the contribution of each source to carbonaceous aerosol in PM2.5 in 2018 winter was consistent with that in 2017 winter:motor vehicle exhaust(48.7%),coal-combustion(28.6%),dust(10.9%),biomass-burning(7.6%),and secondary sources(4.2%).The source apportionment results of carbonaceous aerosol in PM2.5 in Changzhi showed clear seasonal variations in which coal-combustion,biomass-burning and dust were higher in 2017/2018 winter than in 2018 summer(20.3%,4.5%and 7.5%,respectively),while motor vehicle exhaust and secondary sources in 2018 summer(59.2%and 8.5%,respectively)were both significantly higher than in 2017/2018 winter.The analysis of the potential source contribution factors(PSCF)and concentration-weighted trajectory(CWT)of carbonaceous components in Changzhi showed that,in addition to the contribution of local sources,the contributions of OC and EC in 2018 summer were dominated by the contribution of the region around Changzhi,and the pollution of carbonaceous components were more serious in 2017/2018 winter,the contributions of OC and EC were mainly influenced by long-range transmission from the region around Changzhi and from regions such as northern Shaanxi and western Inner Mongolia in the northwest direction.3.The δ13COC values for PM2.5 emissions from coal-combustion,gasoline vehicle exhaust,diesel vehicle exhaust,dust and biomass-burning were-27.45±0.34‰,-24.68±0.37‰,-23.60±0.87‰,-26.35±0.84‰and-16.25±0.61‰,respectively,and the δ13CEC values were-24.49±0.41‰,-26.32±0.25‰,-28.83±0.41‰,-14.22±0.58‰ and-23.50±0.33‰,respectively.The δ13C values were found to be different and could be used for source apportionment of carbonaceous aerosols.4.The δ13COC values exhibited clear seasonal variations in their isotope levels of-23.44±0.64‰ in 2017 winter and-26.81±0.52‰ in 2018 summer,while δ13CEC exhibited no significant seasonal variations in 2017 winter(-25.33±0.74‰)and 2018 summer(-26.37±0.45‰).5.The results of EC source apportionment of PM2.5 in 2017 winter and 201 8 summer in Changzhi obtained using the MixSIAR(Mixture Stable Isotope Analysis in R)model showed obvious seasonal variations,with coal-combustion,biomass-burning,and dust all higher in 2017 winter(22.9%,17.2%,and 6.9%,respectively)than in 2018 summer(14.2%,11.6%,and 4.2%,respectively),and diesel vehicle exhaust in 2018 summer(43.5%)was significantly higher than in 201 7 winter(28.0%).The seasonal variation of gasoline vehicle exhaust was not significant,with contributions of 25.0%and 26.5%in 2017 winter and 2018 summer,respectively.The results obtained by the PMF model were generally consistent with the results of EC source apportionment obtained by using the MixSIAR model mentioned above.The difference could be found in the contribution comparison of some source,like biomass-burning,dust,which was due to the uncertainty of the tests and the methods.Especially,the results of EC source apportionment obtained by the PMF model were affected by source-related tracers during the source identification,which could lead to high uncertainty into the results.Therefore,the carbon isotope approach is more suitable for source analysis of EC than the PMF model.6.Based on the isotope MixSIAR model,the quantitative carbonaceous aerosol analysis method was established to obtain source apportionment results of TC in PM2.5.The results showed that the contribution of sources to TC in PM2.5 in 201 7 winter and 2018 summer were in the same order,in 2017 winter:SOC(26.2%).diesel vehicle exhaust(20.7%),gasoline vehicle exhaust(18.4%),coal-combustion(16.9%),biomass-burning(12.7%),and dust(5.1%);in 2018 summer:SOC(48.4%),diesel vehicle exhaust(22.4%),gasoline vehicle exhaust(13.7%),coal-combustion(7.3%),biomass-burning(6.0%)and dust(2.2%).The results of TC source apportionment obtained by isotope method and PMF model both showd that,except for SOC,the main sources were motor-vehicle-exhaust and coal-combustion,therefore,strengthening the control of motor-vehicle-exhaust and coal-combustion pollution is an important way to reduce carbonaceous aerosol pollution in Changzhi. |
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