大气水溶性有机碳气溶胶的14C和13C同位素来源解析及光吸收特性研究

Water-soluble organic carbon (WSOC) is an important constituent of the total organic carbon aerosol. Since its light absorption shows similar characteristics with brown carbon, WSOC exhibits significant influences on atmospheric chemical processes, radiative forcing and climate change. However, so far there is a lack of awareness of light-absorbing properties of WSOC and the affecting factors. Moreover, the sources of WSOC are still less well-constrained. Therefore, in this project we perform a year-round sampling of ambient aerosols in the typical city Nanjing in the Yangtze River Delta (YRD) in Eastern China. Sources of WSOC with their relative contributions in urban region in YRD will be accurately quantified by the dual carbon isotope signature (radiocarbon 14C and stable carbon 13C) of WSOC. Seasonal variations of sources of WSOC will be revealed. Besides, seasonal variations of WSOC in PM1.0, PM2.5 and PM10 will be characterized. Light-absorbing properties of WSOC in aerosols with different sizes as well as the key affecting factors will be also clarified. In addition, the impacts on light-absorbing properties and source contributions of WSOC under high biomass burning emission will be obtained by the dual carbon isotope, organic tracer and air mass backward trajectory analysis. The potential findings of this project will not only help to better understand the radiative forcing of organic aerosols with its impact mechanism on atmospheric chemical processes and evaluate the contribution to aerosols’ environment and climate effects from different human activities, but also provide a scientific basis for aerosol reduction and control strategy.

水溶性有机碳(WSOC)是有机碳气溶胶的重要成分。由于光吸收表现出棕色碳的特征，WSOC对大气化学过程、辐射强迫与气候变化具有重要影响。然而，目前对WSOC光吸收特征的研究较为缺乏，对WSOC来源的定量研究也有待深入。因此，本项目选择长三角典型城市南京作为研究区域开展为期一年的气溶胶采集，利用双碳同位素(13C和14C)联用技术，定量识别长三角典型城市WSOC的来源权重并揭示及其季节变化规律；明确不同粒径气溶胶(PM1.0、PM2.5和PM10)中WSOC的季节分布特征，阐明各季节不同粒径WSOC的光吸收特性及关键影响因素；结合双碳同位素联用技术、有机物示踪和气团后向轨迹模式，揭示高生物质燃烧排放对大气WSOC光吸收特性与来源的影响。研究成果将有利于深入认识有机气溶胶的辐射强迫及其对大气化学过程的影响，帮助准确评估不同人类活动对气溶胶环境气候效应的的贡献，为有效控制气溶胶污染提供科学依据。

大气水溶性有机碳（WSOC）作为有机气溶胶的重要成分，其光吸收表现出明显的波长依赖性特征，是一类典型的棕色碳，对大气化学过程、辐射强迫与气候变化具有重要影响。项目执行期间，我们研究了城市大气气溶胶的光吸收特性及其昼夜和季节变化规律，评估了大气棕色碳光吸收的贡献，揭示了生物质燃烧对棕色碳光吸收的影响；采集了城市和背景地区大气气溶胶的四季样品，定量研究了WSOC的浓度及其季节变化规律，发现南京地区PM2.5中的WSOC的平均浓度为6.2±2.6 µg/m3；测定了WSOC的碳同位素特征，分析了气溶胶的化学组成，解析了其来源；定量分析了WSOC和甲醇可溶有机碳（MSOC）的紫外-可见吸收光谱，阐明了WSOC和MSOC的吸收系数、质量吸收效率、吸收波长指数等光吸收特性及其季节变化规律，发现南京地区平均Abs365,WSOC为5.38±3.57 Mm-1，MAE365,WSOC为0.84±0.28 m2/g，AAEWSOC为7.93±1.97，Abs365,MSOC平均值为11.05±7.39 Mm-1；分析了棕色碳光吸收与其化学组成的相关关系；基于高分辨液相色谱-质谱联用技术分析了气溶胶中典型的棕色碳分子组成—硝基酚类化合物的分子组成、浓度和季节变化特征，估算了其光吸收能力及对棕色碳消光的相对贡献，并利用正交因子矩阵（PMF）源解析模型解析了典型棕色碳成分的来源，揭示了生物质燃烧和二次生成等对棕色碳的影响，发现南京大气硝基苯酚类化合物的平均浓度为8.4±7.5 ng/m3，365 nm处硝基苯酚类化合物的光吸收贡献主要由NCs类、NSAs类和NPs类产生，秋冬季NCs类的光吸收贡献有所增大，NSAs类的光吸收贡献有所降低。项目研究成果有利于对有机气溶胶的辐射强迫及其环境气候效应的认识，为控制大气气溶胶污染提供科学依据。