使用偏振激光技术针对我国华北地区沙尘颗粒与人为污染物混合演变过程的观测研究

Mineral dust aerosol, one of the most abundant component in the atmosphere, has long been the hottest topic in the aerosol sciences due to its strong environmental and climate effects. In China, mineral dust particles usually mix with substantial amount of pollutants during transport, resulting in large uncertainties in model simulations due to significant changes in its physical, chemical and morphological properties. Till now, numerous of achievements have been reported about the mixing state of polluted dust on the basis of electron-microscopy technique; however manual selection and inspection of single dust particles lead to high-operating cost and a poor statistics. The polarization feature of scattering light is a good surrogate to indicate the change of non-sphericity of dust particles quantitatively with high temporal resolution. Such kind of study is just beginning. In this proposal, an optical particle counter with an advanced laser polarization module is adopted to investigate the evolution of size distribution and polarization characteristics of mineral dust particles during both dust-dominant and pollution-dominant periods. With a combined analysis of chemical compositions, we attempt to quantify the coating effects of water-soluble secondary inorganic matters on the morphological change of dust particles, as well as heterogeneous processes and chemical dynamic mechanics of internally mixed dust particles, in particular the formation of spherical dust particles. This study will provide the scientific basis for improving numerical simulation of climate effects of Asian dust and promotion of environmental management by Chinese government.

沙尘是大气气溶胶的主要组成，具有很强的环境和气候效应，一直是国际气溶胶科学研究领域的热点。在我国，矿物气溶胶在传输过程中可吸附大量污染物，其理化特性和外部形貌的改变使其气候效应的评估存在巨大的不确定性。到目前，科学家使用电镜技术对沙尘气溶胶的混合状态的研究取得了大量成果，但该方法需人工对单个颗粒物进行甄别和观察，分析成本较高。颗粒物散射光的偏光率可表征其外部形貌的改变，具有实时和定量化的优点，国际上相关研究刚刚起步，系统性的成果还比较匮乏。本研究拟采用最新的单颗粒偏振激光检测技术研究沙尘和灰霾污染生消过程中，不同粒径沙尘气溶胶散射光偏光率的动态演变特征，结合化学成分定量分析不同气象条件下硝酸盐等可溶性二次无机物对沙尘外部形貌的影响，探讨沙尘气溶胶和人为污染内部混合的非均相化学反应及其相应的动力学机制。为我国沙尘气溶胶气候效应数值模拟和环境治理提供科学依据。

本课题对中国北部典型沙尘输送通道城市上，大气边界层沙尘气溶胶颗粒物理化特性、混合状态演变及环境效应进行了研究，取得的科研成果主要包括：（1）利用单颗粒检测偏振激光技术，结合搭载偏振激光雷达的卫星（CALIOP）遥感技术，在东亚地区开展长期的大气气溶胶退偏性质观测研究，对东亚气溶胶输送过程中沙尘颗粒物混合状态的演变特征以及气象相互作用进行了系统表征，分析陆地典型污染城市气溶胶浓度和偏光性质的粒径谱分布、季节变化趋势等，明晰东亚地区环境大气总体颗粒物的形貌和混合状态特征。（2）准确识别典型沙尘过程、人为污染过程以及二者（沙尘与人为污染物）的混合污染过程，利用后向轨迹模式、天气形势分析等识别典型沙尘污染时段的污染物来源，探讨沙尘颗粒物在东亚污染城市大气边界层内，与人为污染物发生内部混合的必要气象和污染条件。系统分析了东亚自然源-人为气溶胶混合过程对区域空气质量的影响，拓宽了对沙尘气溶胶生态环境效应的认识。（3）基于单颗粒偏光性质的探测结果，为未来激光雷达气溶胶种类的精确识别提供指导，同时可帮助优化沙尘传输模式在沙尘过程模拟方面的表现。