基于前向小角度散射的气溶胶单粒子形态分类

Morphology (size and shape) of Airborne particles plays a majoy role in the climate effects, atmosphere physical and chemical processes, human health and radiation transfer through atmosphere. Measuring spatial angular-resolved elastic scattering is the most popular method for obtaining morphological information of particles. Because of the extremely complicated scattering patterns the inversion process is too tough to obtain a unambiguous morphology, not mention measuring speed. Particle mophology relates to its source and chemical composition, and has the potential application for characterizing, classifying, and identifying. The purpose of this proposal is of developing a method for rapid classifying airborne particles. And the objective is of rapid mophology classification for individual aerosol particles. This project is focusing on the relationship between single particle's mophorlogy and light scattering intensity distribution. A experimental setup is going to established with the ability of simultaneously measuring aerodynamic size and scattering intensity at small forward angles of single particle in-flight. Based on experiment upon aerosol samples composed of known particle size and shape s, statistic analysis method is going to be used to exploring the inversion algorithm and discrimination ability. This research will provide a noval tool for atmosphere science and aerosol science. The techniques developed in this project have great potential in the application of aerosol monitoring and identifying due to the characteristics of continuous, rapid and in-situ measurment, and the integration ability with other optical investigation methods, such as laser induced-fluorescence.

大气颗粒物的形态（尺寸与形状）在气候效应、大气物理化学过程、人类健康以及大气辐射转移中都起着关键性作用。空间角分辨弹性散射光测量是获取颗粒物形态信息的主要方法，但由于散射强度图样的复杂性使得形态反演非常困难，难以获取理想的形态参数和测量速度。颗粒物形态与其来源或化学组分密切相关，有潜力用于大气颗粒物的种类识别。本项目以发展大气颗粒物快速识别方法为目的，以实现气溶胶单粒子快速形态分类为目标，深入研究单粒子形态与光散射空间强度分布的关系，建立可同时测量气溶胶单粒子近前向角分辨光散射分布和空气动力学直径的实验装置，实验研究已知形态颗粒物的光散射性质，基于统计分析方法，探索颗粒物形态特征的反演算法及甄别能力，为大气科学与气溶胶科学等领域提供新的研究手段。本项目研究的技术方法，具有连续、快速以及在线检测的特点，并容易与激光荧光等其他光学探测技术集成，在大气颗粒物监测与识别方面具有很大的应用潜力。

基于形状与尺寸的光散射技术广泛用作颗粒分类的工具。气溶胶粒子的尺寸与形状决定了它们在空气中的行为，包括产生与消失、输运与沉降，有助于追溯其来源或评估污染程度。快速测量尺寸与形状的方法可以用于从背景气溶胶中识别冰晶、灰尘、纤维及生物气溶胶等。.为了快速获取气溶胶粒子尺寸与形状特性的目的，研制了能够同时测量单粒子空气动力学直径和形状参数的实验装置（可称为气溶胶动力学尺寸和形状分析器）。颗粒物形状通过三个光电倍增管对间隔120度方位角的近前向散射光响应的差异值获取，空气动力学直径由粒子通过双激光束的飞行时间获取。.为了获得更好的粒子计数效率和形状识别能力，研究了两种气溶胶进样结构和多种光学结构（参数）。实验测量了球形、立方形和细长形的气溶胶颗粒物样本，初步结果表明实验装置具有较好的区别球形与不规则形状粒子的能力，如从球形液滴中识别结晶NaCl的灵敏度和特异度分别达0.85和0.86，空气动力学直径有助于识别粒子的形状。.尝试进行了若干生物气溶胶的测试实验，如大肠杆菌，枯草芽孢杆菌，都可以较好地与球形粒子区别。初步测量了多种气候条件下室内、室外环境大气气溶胶粒子，观察到各种情况下的非球形粒子数量具有差异，暗示了颗粒物的组成与大气水汽含量的关系。.基于实验装置的光学结构，计算了三个近前向探测器的响应强度与粒子尺寸、折射率、取向以及形状特征的关系。结果表明，该实验装置适合区分直径大于1.0 微米的球形和长形粒子。.若干种类气溶胶粒子的计算分析显示，结合空气动力学粒径，枯草芽孢杆菌、类鼻疽伯克氏菌等生物气溶胶颗粒可以被区分。对长形结晶核黄素颗粒的散射图样计算进行了分析，显示了与实验结果很好的相似性。.实验装置有很大的潜力发展为大气气溶胶监测应用仪器，因为形状与尺寸信息的结合可以更好地区别颗粒物种类。如应用于云层研究中的水滴与冰晶区别，及大气生物气溶胶监测等。