西安市大气棕碳污染特性及发色团种类

Pollution Characteristics and Chromophore Types of Brown Carbon in Xi’an

为探究西安市大气棕碳(BrC)的光学特性及化学组成,利用大气颗粒物采样器和吸附剂同时采集了颗粒相和气相大气样品,并运用紫外-可见分光光度计和三维荧光光度计测定了样品中BrC的吸光和荧光特性,基于平行因子分析(PARAFAC)法解析三维荧光光谱得到BrC的种类和组成信息.结果表明,在波长为365 nm时,颗粒相和气相BrC的吸光度分别为(13.8±7.9) Mm_(-1)和(8.0±3.1) Mm_(-1),两者占比分别为63%和37%.本研究并未发现气相和颗粒相BrC吸光度之间有显著的相关性.PARAFAC结果表明,西安市大气BrC含有类腐殖质发色团、类酚类发色团和类蛋白发色团,而它们分别在气相和颗粒相BrC中的占比是不同的,类腐殖质发色团和类蛋白发色团在颗粒相中分布较多,分别为41%和36%,而气相中主要包含酚类发色团,其占比为78%.本研究结果揭示了气相BrC也可能是贡献大气正辐射强迫的重要因子,以及参与大气光化学反应的重要大气组分,将来的研究需要给予足够重视和关注.

To explore the optical characteristics and chemical composition of atmospheric brown carbon(BrC) in Xi’an,particulate phase and gas phase atmospheric samples were collected using an atmospheric particulate sampler and adsorbent,and the samples were analyzed using an ultraviolet-visible spectrophotometer and a three-dimensional(3D) fluorescence photometer.The absorption and fluorescence properties of BrC were analyzed using the parallel factor analysis(PARAFAC) method to obtain type and compositional information.The results show that at a wavelength of 365 nm,the absorbances of the BrC particulate and the gas phases were(13.8 ±7.9) Mm_(-1) and(8.0 ± 3.1) Mm_(-1),with proportions of 63% and 37%,respectively.No significant correlation was found between the absorbance of the gas and particulate phases.PARAFAC results show that in winter,atmospheric BrC in Xi’an is composed of humiclike and protein-like chromophores, with different proportions in the gas and particulate phases.Humic-like and protein-like chromophores are dominant in the particulate phase(41% and 36%,respectively),while the gas phase mainly contains phenolic chromophores(accounting for 78%).These results reveal that gas phase BrC may be an important factor contributing to positive radiative forcing in the atmosphere as well as an important atmospheric component that participates in atmospheric photochemical reactions.