西安市冬季PM2.5中WSOC的光谱特性和来源解析

Spectral Characteristics and Source Analysis of WSOC of PM in Winter of Xi’an

利用紫外-可见吸收光谱法、三维荧光-平行因子分析法(EEMs-PARAFAC)和后向轨迹模型等,分析西安市冬季PM2.5中水溶性有机物(WSOC)的光谱特性和来源.结果表明,西安市PM2.5中WSOC的浓度为4.66~14.75μg·m-3.WSOC的E2/E3、E3/E4、S275-295、SUVA254、AAE和MAE365的值分别为2.85~4.32、2.21~3.56、0.0099~0.0127 nm^-1、2.35~3.89 m^2·g^-1、2.66~4.60和1.51~2.60 m^2·g^-1.南郊(西安建筑科技大学)采样点PM2.5中WSOC的E2/E3值、E3/E4值、S275-295和AAE值均较高于北郊(城市运动公园)采样点的,而SUVA254和MAE365值较低.EEMs-PARAFAC模型鉴别出WSOC中主要含有4个荧光组分,C1和C2分别归属为类富里酸和类蛋白,C3和C4均归属为类腐殖质,各荧光组分的荧光强度及其总和与PM2.5、OC、WSOC浓度和A254值呈显著正相关(P<0.01).WSOC的FI、BIX和HIX值分别为1.75~2.12、1.14~1.46和1.18~2.06.监测期间气团传输轨迹以本地西南向短距离传输为主,其轨迹占比超过50%;新疆、内蒙古和甘肃等地区冬季污染物排放对西安也有较明显的贡献.西安市南北郊PM2.5的碳组分含量存在差异较小,南郊(西安建筑科技大学)采样点PM2.5中WSOC的相对分子质量、腐殖化程度和光吸收能力比北郊(城市运动公园)的低,而光吸收强度的波长依耐性相对较强.WSOC主要为生物来源或由生物来源和陆源共同组成,且以自生源为主,陕西省区域输送对冬季PM2.5和WSOC的来源贡献最为显著.

The spectral characteristics and sources of water-soluble organic compounds(WSOC)in PM2.5 in winter were studied by using UV-vis absorption spectroscopy,three-dimensional fluorescence spectroscopy,parallel factor analysis,and backward trajectory model.The results showed that the concentration of WSOC in PM2.5 was 4.66-14.75μg·m-3.The values of E2/E3,E3/E4,S275-295,SUVA254,AAE,and MAE365 of WSOC were,respectively,in the range of 2.85-4.32,2.21-3.56,0.0099-0.0127 nm^-1,2.35-3.89 m^2·g^-1,2.66-4.60,and 1.51-2.60 m^2·g^-1.The E2/E3,E3/E4,S275-295,and AAE values of WSOC at the sampling site in the southern suburb of Xi’an,China(Xi’an University of Architecture and Technology)were higher than those at the sampling site in the northern suburb(sports park),while the values of SUVA254 and MAE365 were lower.There were four fluorescent components in WSOC identified by the EEMs-PARAFAC model:C1 and C2 were fulvic acid-like and protein-like,respectively,and C3 and C4 were humus-like components.The fluorescence intensities and the sum of the fluorescent components were positively correlated with the concentrations of PM2.5,OC,WSOC,and A254 value(P<0.01).The fluorescence index(FI),biological source index(BIX),and humic index(HIX)values of WSOC were 1.75-2.12,1.14-1.46,and 1.18-2.06,respectively.During the monitoring period,the air mass transmission trajectory was dominated by the local southwest of short-distance transmission,and its trajectory accounted for more than 50%.The pollutant emissions from Xinjiang,Inner Mongolia,and Gansu also made significant contributions to the air pollution levels in Xi’an in winter.There was a small difference in the carbon component content of PM2.5 in the northern and southern suburbs of Xi’an.The molecular weight,humification degree,and light absorption capacity of WSOC at the southern suburb sampling site were lower than those in the northern suburb where the wavelength dependence of light absorption intensity was relatively stronger.The WSOC mainly originated from biological sources or both from biological and terrestrial sources.Local transmission had the most significant contribution to PM2.5 and WSOC in winter.