城市PM2.5中含氮棕碳气溶胶的特征及环境演化

含氮棕碳(nitrogen containing brown carbon，N-BrC)是棕碳的重要组成部分，其显著的吸光效应和复杂的化学组成对区域雾霾形成、人体健康和辐射强迫有重要的影响。已有研究表明N-BrC是气溶胶颗粒棕色化（Browning）的关键因素之一。而N-BrC来源广泛、结构复杂、二次转化机制多样、分子组成以及分子团簇结构更是尚未清晰界定，无法正确认识N-BrC的分子组成及光学演化特征。本项目通过在西安市开展冬夏季正常天气和污染事件的高分辨率PM2.5观测，利用傅里叶变换离子回旋共振质谱分析其分子组成，揭示光化学反应和水相反应过程N-BrC分子组成变化。同时，利用量子化学计算方法分析N-BrC的分子单体及团簇的光学效应。本项目把观测实验和理论计算相结合，在分子水平上揭示N-BrC在二次反应过程中分子组成，团簇结构及光学性质的演化特征。

Nitrogen containing brown carbon (N-BrC) is an important component of brown carbon. The remarkable absorption effect and complex chemical composition have a profound impact on haze formation, human health, and radiative forcing. It has been reported that N-BrC is one of the key factors in Browning of aerosol particles. N-BrC has a wide range of sources, complex structures, diverse secondary transformation mechanisms, molecular composition, and molecular cluster structure. At present, very limited study was carried to understand the N-BrC formation and its optical properties variations. Therefore, this project investigates the evolution mechanism of N-BrC in the environment by carrying out high-resolution PM2.5 observation of pollution events in winter and summer in Xi'an. The molecular composition will be analyzed by Fourier transform ion cyclotron resonance mass spectrometry, especially the variations between photochemistry and aqueous phase reaction processes. Meanwhile, the optical effect of molecular monomer and cluster of N-BrC will be analyzed by quantum chemistry calculation. Theoretical calculations and experiments are joint in this study to understand the variations of molecular composition, molecular cluster structure, and optical properties of N-BrC during the processes between photochemical and aqueous reaction in Xi'an. The research results will help to better understand the formation, absorption and environmental effects of N- BrC.