Chemical Composition And Source Apportionment Of Atmospheric Particulate Matter In Lanzhou

Atmospheric particles not only participate in the formation of clouds and rain,reduce atmospheric visibility,change atmospheric radiation and then affect the global climate,but also harm human health.In recent years,the process of industrialization and urbanization continues to accelerate and the problem of particulate pollution in China continues to intensify.As an old industrial city in northwest China,Lanzhou is still suffering from severe pollution.In this study,the panxuan road Campus of Lanzhou University in Lanzhou was selected as the sampling site and the atmospheric particulate matter samples were collected from May 2020 to April 2021.The chemical components of the samples were measured by instruments and the seasonal variation characteristics of the mass concentration of atmospheric particulate matter and chemical components were analyzed.At the same time,the differences of atmospheric particulates and their chemical components under different weather events were compared and analyzed.Finally,the main sources of atmospheric particulates were analyzed by using backward air mass trajectory,potential source region contribution method,weight trajectory concentration method and positive definite matrix factor analysis method.The results show that the mass concentration of atmospheric particulate matter in Lanzhou was higher than that of the 2^th National Ambient Air Quality Standard（NAAQS）,indicating that Lanzhou is still relatively serious air pollution.Atmospheric particles were generally alkaline and their chemical components mainly include organic matter,EC,water-soluble ions and other unknown components,with significant seasonal characteristics of each chemical component.The carbonaceous component showed the seasonal characteristics of high in autumn and winter and low in spring and summer,which was affected by various factors.The secondary carbonaceous component was generated during the whole sampling period.The mass concentration of water-soluble ions in the order of mass concentration was NO₃^->SO₄^2->Cl^-;Ca²⁺>NH₄⁺>Na⁺>K⁺>Mg²⁺.Secondary ions existed in different forms and were important components of water-soluble ions.Both of them showed the diurnal characteristics of high at daytime and low at nighttime.However,the differences of weather events and meteorological conditions in different seasons resulted in different seasonal characteristics.The NO₃^-/SO₄^2-ratio indicated that the atmospheric particles in Lanzhou were mainly from mobile sources.The functional groups in atmospheric particles were mainly composed of organic parts such as hydroxyl group of 3400—3700 cm^-1,ions and inorganic parts related to sand and quartz filter membrane with significant seasonal characteristics.Spectral clustering showed that the samples were mainly from traffic emissions,secondary aerosols and fossil fuel combustion,biomass combustion,dust source and soil source.Under different weather events,the mass concentration and chemical components of atmospheric particulate matter in Lanzhou were significantly different.PMF source analysis confirmed six main sources of atmospheric particulate matter in Lanzhou:traffic source,biomass burning,road dust,soil dust,coal burning and secondary aerosol formation processes.Air agglomeration indicated that the atmospheric particulate matter in Lanzhou mainly came from long-distance transmission in northwest,west and local air mass,the potential source area was mainly the potential contribution zone corresponding to the dust source area and local source,both of which played a great contribution to the atmospheric particulate matter mass concentration in Lanzhou.The above results indicated that air pollution in Lanzhou is still serious,more attention should be paid to the above mentioned sources and regional joint prevention and control when the prevention and control measures are designated,which is of great significance to improve the air environmental quality in Lanzhou.