Pollution Characteristics And Source Apportionment Of Fine Atmospheric Particles In Luoyang

In the process of urbanization in China,the increasement of energy consumption andmotor vehicle ownership,the problem of air pollution is becoming more and more seriously.The combined atmospheric pollution,which is dominated by ozone and fine particles,has become a major environmental problem that needs to be controlled in China.Different from gaseous pollutants,the behavior and transformation of atmospheric particulate matter in atmosphere and its effects on climate,environment and human health are not only dependent on its mass concentration,but also related to its particle size,particle spectrum distribution,optical characteristics,chemical composition and atmospheric lifetimes.Therefore,the study in physical characteristics and chemical composition of atmospheric particulate matter is helpful to further study the environmental behavior and climate effect of atmospheric particulate matter.By setting up observation sites in Luoyang,through sampling collection and chemical composition analysis,the interannual variation trend and seasonal pattern of PM_2.5 in Luoyang were systematically explained.The formation mechanism and possible source of atmospheric particulate matter are described.The study drew the following main conclusions:1.303 PM_2.5 samples were collected from April 16 to December 29,2015 to analyze the elements,water soluble inorganic ions,organic carbon and elemental carbon.The annual mean concentration of PM_2.5 was 142.3μg/m~3,and 75%of the daily PM_2.5 concentrations exceeded the 75μg/m~3.The secondary inorganic ions,organic matter and mineral dust were the most abundant species,accounting for 39.6%,19.2%and 9.3%of the total mass concentration,respectively.But the major chemical components showed clear seasonal dependence.SO₄^2-was most abundant specie in spring and summer,which related to intensive photochemical reaction under high O₃ concentration.In contrast,the secondary organic carbon and ammonium while primary organic carbon and ammonium significantly contributed to haze formation in autumn and winter,respectively.This indicated that the collaboration effect of secondary inorganic aerosols and carbonaceous matters result in heavy haze in autumn and winter.Six main sources were identified by positive matrix factorization model:industrial emission,combustion sources,traffic emission,mineral dust,oil combustion and secondary sulfate,with the annual contribution of 24%,20%,24%,4%,5%and 23%,respectively.The potential source contribution function analysis pointed that the contribution of the local and short-range regional transportation had significant impact.This result highlighted that local primary carbonaceous and precursor of secondary carbonaceous mitigation would be key to reduce PM_2.5 and O₃during heavy haze episodes in winter and autumn.2.During the sampling period from 2018 to 2019,the average PM_2.5 mass concentration in Luoyang was 97.0μg/m~3.The number of clean days increased significantly,and the number of days with heavy pollution in autumn and winter decreased significantly.The annual ratios of secondary inorganic aerosols,carbonaceous components and inorganic elements were 40%,20%and 5%,respectively.The dominant species of secondary inorganic aerosol component changed to nitrate.In the four seasons,the formation process of moderate pollution was all caused by the rapid increase of NO₃^-,while in winter,the dominant composition of heavy pollution changes to the carbonaceous aerosol.The results of source apportionment were secondary nitrate（27.7%）,vehicle emission（24.0%）,mineral dust（15.1%）,secondary sulfate（14.0%）,industrial process（12.8%）and combustion（6.4%）.3.Backward trajectory model analysis shows that:During the sampling period of 2015,the air mass mainly came from the Fen-Wei Plain and the Beijing-Tianjin-Hebei region around Luoyang.During the sampling period of 2018,the air mass mainly originated from northwest and northeast in autumn,winter and spring.The source of the dominant air mass has certain seasonal patterns,the dominant air mass in autumn and winter is mainly from the northeast,the air mass from the west is more in spring,and the air mass from the eastern coastal area in summer is worth paying attention to.In 2015,the potential source areas of Luoyang were relatively concentrated,mainly distributed in the northwest and northeast directions.In the autumn of 2018,the potential source region was mainly located in the northwest and southeast,in winter,it was mainly located in the southwest and northeast,in the spring of 2019,it was mainly located in the northwest and south regions,and in summer,it was mainly located in the eastern coastal areas.In autumn and winter,the coverage area is the largest,relatively concentrated,and the contribution of high value areas is significant.In summer,the potential contribution area is the smallest and located to the east.