广州城区秋冬季大气颗粒物中WSOC吸光性研究

Light Absorption Properties of Water-Soluble Organic Carbon(WSOC) Associated with Particles in Autumn and Winter in the Urban Area of Guangzhou

主要对广州秋季(2014年9月)和冬季(2014年12月~2015年1月)大气PM_(2.5)和不同粒径段颗粒物样品中水溶性有机碳(WSOC)的吸光性进行了研究.结果表明,PM_(2.5)上WSOC的光吸收波长指数(AAE_(abs))秋、冬季分别为3.72±0.41和3.91±0.70,低于北京和北美地区测量结果.WSOC在365 nm波长的质量吸收效率(MAE)秋、冬季分别为0.52 m^2·g^(-1)和0.92m^2·g^(-1),两个季节具有明显的差异.冬季WSOC的MAE值呈现随粒径增大而降低的趋势;而秋季所有粒径段颗粒MAE_(WSOC)都比冬季低,特别是<0.95μm粒径段颗粒降低得更多,这表明秋季颗粒物中WSOC二次源的贡献更大一些,而且主要是富集在亚微米级颗粒物上.此外,对比本研究以及文献中报道的元素碳(EC)和WSOC的MAE值,可以发现在颗粒物受一次源排放影响较大的情况下,WSOC对于颗粒消光的贡献是不容忽视的.

Light absorption properties of water-soluble organic carbon（WSOC） were investigated in the urban area of Guangzhou.The fine particulate matter（PM2.5） and size-segregated samples were collected in September and December of 2014 and January of 2015.The variation of absorption with wavelength of WSOC was characterized by the absorption Angstrom exponent（AAE（abs））.The AAE values of WSOC in PM2.5 were 3.72 ±0.41 in autumn and 3.91 ±0.70 in winter,which were lower than those in Beijing and north America.The mass absorption efficiency（MAE） of WSOC at 365 nm wavelength was 0.52 m^2·g^-1 in autumn and 0.92 m^2·g^-1 in winter,exhibiting distinct variations between autumn and winter.In winter,the MAE（WSOC） values exhibited a decreasing trend with increasing particle size,and all size-segregated MAE（WSOC） values in autumn were lower than those in winter,particularly for the particles 0.95 μm,suggesting more contribution of the secondary formation to WSOC.Comparing the MAE values of elemental carbon（EC）and WSOC,it could be found that the contribution of WSOC to the light extinction of particles couldn＇t be ignored when the particles were mainly emitted from primary sources.