Characteristics And Sources Apportionment Of Size-Segregated Atmospheric Particles In Lhasa

Due to special climate regime and different energy consumption structures,the atmospheric environment in Lhasa is unique and low environmental tolerance.Therefore,the characters of atmosphere pollution in Lhasa is different from other cities and worthy of further study.Size distribution and composition(e.g.metal elements and carbonaceous aerosol)of atmospheric particular matter(PM)decide the qualitative and quantitative effects on human health and environment.The samples of atmospheric particular matter in urban area of Lhasa were collected from August 2018 to May 2019 by STAPLEX large-flow grading sampler(96 sets).The mass concentration of size-segregated organic carbon(OC)and elemental carbon(EC)were analyzed by the DRI-2001A;and qualitative analysis of secondary organic carbon(SOC).The concentrations of metal elements in atmospheric particular matter were analyzed by the ICP-MS;the characteristics of size distribution and seasonal variation,enrichment factors,correlation analysis were studied with meteorological conditions.Source analysis of seven carbonaceous components and metal elements in Lhasa was performed using the Principal component analysis(PCA).Results showed that the mass concentration of size-segregated OC and EC was bimodal.The highest level of OC mass concentration appeared in the particulate matter smaller than 0.49μm,and the second highest one existed in the particulate matter with the size ranging from 1.5 to 3.0 μm(winter)and from 3.0 to 7.2μm(expect winter).EC was mainly distributed in the particulate matter smaller than 0.49 μm.The correlation between OC and EC was good(<0.49 μm and 0.95-1.5 μm);The correlation between OC and EC was poor(0.49-0.95 μm,1.5-3.0 μm,>7.2μm and 3.0-7.2 μm),which suggested that OC had other sources.Besides combustion sources,biological emissions and organic matter converted from gas to particles were sources of OC.Furthermore,the OC/EC mass ratios at various particulate sizes(10.3～21.1)indicating that there was the pollution of SOC in Lhasa.The mass concentration of size-segregated Na,Mg,Al,Ca,Pb,Ti,Mn,Fe,Cr and Zn presented bimodal(<0.49 μm and>7.2 μm);In PM3.0,the crustal elements of Al,Mg,Ca,Fe,Mn had significantly strong correlations(r>0.7);Ni and V existed Strong correlations;the correlations of Cu and Zn was weak(r=0.148).In PM3-10,the correlations between Ca and Al,Mg,Fe,Mn were general.The correlations of Pb,Al,Mg,Fe and Mn were strong(r>0.7);Cu and Zn had a significantly strong correlations(r>0.7).According to the values of EFs,the elements were divided into three groups:slightly enriched elements including Ca,Ti,Mg,Fe,Mn,Mg;moderately enriched elements(Ni、V、K、Na、Co、Cr);highly enriched elements(Cu、Zn、Pb).Source analysis of seven carbonaceous components and metal elements in Lhasa was performed using the Principal component analysis(PCA).The results showed that the main pollution sources of carbonaceous particulate matter in Lhasa are coal burning,motor vehicle exhaust,biomass combustion and soil dust.Biomass combustion and soil dust are the main sources of OC;coal and motor vehicle exhaust are the main sources of EC.In PM3.0,the main sources of atmospheric particulate matter were combustion emissions and floating dust,followed by traffic emissions(wear of tires and brake pads,etc.).In PM3.0-10,the main sources of atmospheric particulate matter were floating dust,building dust and copper mine.