典型污染天气黑碳气溶胶混合形态、表面结构、光吸收性质及其关系

The study on the climate effects of aerosols is focused currently in the forefront fields of atmospheric chemistry and the related areas. This project will take the typical fog-haze pollution of atmosphere as the research background, and take the Yangtze River delta as an example. Single-particle aerosols will be characterized though the coupling of aerosol time-of-flight mass spectrometer (ATOFMS), single particle soot photometer (SP2), and electron microscope (TEM/SEM), to understand distribution characteristics of particle sizes, mixing states, chemical compositions, and surface structures of black carbon aerosols, as well as key components in the different types of atmospheric pollution. Aerosol extinction and scattering coefficient will be measured online with a cavity ring-down laser spectrometer (CRDs) coupled with a nephelometer. Absorption coefficient, single scattering albedo (SSA), and ångström exponent (å) of aerosols can be then calculated precisely. On this basis, single-particle characterization, the information of total particle phase and optical parameters will be considered synthetically, to analyze light absorption properties of aerosols in the pollutant days, and to clarify the influence laws of mass concentrations, mixing states and surface structures of black carbon aerosols on light absorption intension. The smooth implementation of this project will help to assess direct radiation force value of aerosols in the Yangtze River delta region, and to clarify comprehensively the essential relations among aerosols, climate change and regional atmospheric pollution in this region, both of which will provide new clues and evidences for forecasting climate change on the globe.

气溶胶的气候效应是当前大气化学及相关领域的研究热点和前沿课题。本项目以典型雾、霾污染天气为背景，以长江三角洲为例，基于气溶胶飞行时间质谱（ATOFMS）、单颗粒黑碳测量仪（SP2）、电子显微镜（TEM/SEM）等先进技术表征单颗粒气溶胶，理解黑碳气溶胶及关键成分在不同类型污染天气的粒径、浓度、形态、结构等分布特征。利用光腔衰荡激光光谱仪（CRDs）、三波长浊度计（Nephelometer）在线测量气溶胶消光和散射系数，准确计算光吸收系数、单次散射反照率和折射指数。在此基础上，综合单颗粒物表征、总颗粒物相信息及气溶胶光学参数，分析污染大气气溶胶光学特性，阐明黑碳气溶胶质量浓度、混合态、表面结构对气溶胶光吸收强度的影响规律。本项目的顺利实施，有助于准确评估长三角地区气溶胶直接辐射强迫值，全面剖析长三角地区气溶胶、气候变化及区域大气污染之间的本质联系，可为预测全球气候变化提供新的理论线索和依据。

气溶胶光学性质与气溶胶的气候效应密切相关，与气溶胶的尺寸、形态及混合状态密切相关，相关研究是大气科学的热点和前沿。本项目采用TEM-EDX，及NEXAFS等单颗粒分析手段，气溶胶可以分为，S-rich, N-rich, K-rich, soot, metal particles, fly ash, mineral dust, organic particles等，发现雾霾污染天气与清洁天气各类气溶胶颗粒占比显著不同。在分析单颗粒形态的基础上，采用光腔衰荡光谱仪结合三波段浊度计，对比北京城区清洁、雾和霾污染天气状况下气溶胶混合态，光学特性及其内在关系进行了研究。结果表明，清洁天气气团从北方引入少量矿尘颗粒物。当大雨发生过后，矿尘等大颗粒物被大部分雨除，使颗粒物平均尺寸减小（GMD~0.5 μm）。清洁天颗粒物浓度低，且主要处于外混状态，导致光吸收和散射较低。相对的，灰霾和雾期间有更高的颗粒物浓度，更大的平均粒径（GMD~1 μm）和更低的能见度，AOD值最高可达清洁天的7倍。从工厂排放的金属和飞灰颗粒等污染物在稳定大气条件下聚积。在观测后期，气团经过密集的南方秸秆燃烧区域进入采样点，携带了大量生物质燃烧颗粒物，如黑碳和富K颗粒物，导致长时间的严重灰霾。气溶胶光散射和光吸收性能由于黑碳的内混态以及粒径分布增大而大大增强，与清洁天相比光吸收能力增强的倍数是黑碳浓度增加的8倍多。在雾天气条件下，41%的黑碳包含在硫酸盐、硝酸盐及有机物中。硝酸盐和硫酸盐等非吸光物质的聚焦作用，使气溶胶颗粒的光吸收能力显著增强。当前研究表明气溶胶混合态显著影响气溶胶光学性质，及其主导的气候效应。