北京地区重霾过程气溶胶颗粒密度分布及形貌因子演化的观测研究

Aerosol particles have important effects on air quality, human health, climate, regional visibility, and the deposition of acidic and toxic substances. The properties of aerosol particles with respect to each of these issues are strongly affected by particle size distribution, morphology, and chemical composition. All of these properties may vary depending on the source and aging history of particles. For these complex properties of aerosol particle, the particle density can act as a good predictor and receive more and more concern recently. However, the majority of published work focuses on laboratory generated aerosols and obscuring a deeper understanding of the ambient particles. Atmospheric particulate pollution of Beijing is a major concern. Due to the industrial pattern and urbanization of Beijing, there are complex sources of primary aerosols which contain abundant chemical composition with great varying range. This project will first setup a comprehensive field experimental system coupled with laboratory experiments for studying the complex atmospheric transfer and evolution of aerosol particle during heavy haze pollution episodes in Beijing. Based on the measured physical and chemical characteristics of aerosol particles, the density and morphological evolution model will be constructed through numerical simulation. The density evolution of aerosol particle under multi-factor such as gaseous pollutants and meteorological parameters will be investigated. Relationship between density evolution and its morphology transformation will be explored based on the morphology model and some assumption, which are then used to determine the relative contribution of organic and inorganic components to the rapid formation of secondary aerosol during the heavy haze pollution episodes. This project will provide effective experimental data and theoretical support for understanding the aging mechanism of aerosol particle and its role in affecting light extinction in air pollution complex, and provide scientific guideline and theory evidence for policy makers to introduce suitable strategy under haze weather.

气溶胶颗粒密度是连接其物理和化学特性的重要纽带，其形貌特征亦对其在大气环境的演化过程具有重要表征作用。申请项目拟以重霾污染过程为研究背景，基于外场观测和可控实验，构建气溶胶颗粒密度分布及形貌因子的拟合算法，定量表征城市大气复合污染条件下气溶胶颗粒表观密度及形貌因子演化过程和变化规律及其与气态前体物和气象要素的关系。进一步揭示气溶胶颗粒表观密度和形貌因子与其化学成分、粒径分布以及老化程度的内在关系，剖析重霾污染过程有机/无机成分对二次气溶胶颗粒形成的相对贡献，阐述重霾污染过程颗粒物快速增长的物理过程和化学机制，探索气溶胶颗粒形貌演化对其消光特性的影响，为制定霾污染调控策略和治理措施提供科学依据。

气溶胶颗粒的密度分布对其在大气环境的演化过程具有重要的表征作用。然而目前相关的工作仍集中在实验室研究，关于实际大气环境中气溶胶颗粒密度分布的认识仍然十分有限。为揭示城市复杂大气环境中气溶胶颗粒密度分布的变化特征及其影响因素，本项目在北京地区针对大气颗粒物的数浓度谱分布、质量浓度和成分组成等理化参量进行了常规外场观测与可控实验相结合的中长期观测，结合构建的气溶胶颗粒及形貌因子表征方法，系统分析了该地区气溶胶颗粒密度分布的季节/日变化规律，发现气溶胶颗粒密度呈现明显的季节变化特征（冬春高、夏秋低），与气象要素和颗粒物成分的季节演变密切相关。气溶胶颗粒密度的日变化受局地一次排放和二次生成影响，即气溶胶颗粒密度低值出现在早晚交通高峰时段，而高值出现在中午光化学反应最强的时间段。细颗粒物形貌因子的年均值接近1；表明北京地区气溶胶颗粒整体接近球形，气溶胶老化程度较高。从形貌因子的季节分布来看，春季和秋季气溶胶老化程度相对较高；而夏季和冬季气溶胶颗粒主要为形状不规则的非球形，受局地排放源的影响更大。利用实验室可控实验研究了单分散气溶胶粒子表观密度，发现50nm和200nm的气溶胶颗粒呈现独特的双峰型分布，并且进一步根据表观密度辨识为两种来源的气溶胶粒子群，即含碳粒子群（ρapp=1.0 g/cm3 ）和二次无机气溶胶粒子群（ρapp=1.8 g/cm3），揭示了一次排放的颗粒物和二次生成/区域输送的颗粒物在城市大气环境中的演化过程。在获取单分散气溶胶粒子表观密度随粒径变化的响应关系上，进一步探讨了重霾污染过程不同粒径气溶胶粒子形貌因子的演变规律，揭示了有机和无机组分对颗粒物快速增长的相对贡献。项目发表SCI论文4篇，在国内外学术会议作报告4次，培养博士后和研究生5人，博后出站和博士毕业2人。研究成果有助于深入理解重霾污染事件中颗粒物快速增长的物理过程和化学机制，并为后续制定霾污染调控策略和治理措施提供数据基础和技术支撑。