Developing new laser-based instruments to characterise optical properties of aerosol particles from road traffic

在英国，道路交通仍然是颗粒物(PM)污染的最主要来源之一。随着尾气排放的下降，PM的非废气来源--包括再悬浮的道路粉尘、轮胎和刹车摩擦--变得越来越重要。非排气PM现在被认为是排气源的主导。1影响非排气排放的因素人们知之甚少，因此很难制定减少PM的解决方案，也很难预测随着电动汽车和混合动力汽车变得越来越流行，未来的变化。此外，决定气候和公共健康影响的这些颗粒物的物理特征存在很大的不确定性。光学仪器在高(~1赫兹)时间分辨率的大气气溶胶现场测量中得到了广泛的应用。为了检索有关颗粒大小和折射率的定量信息，通常需要数学模型来反演原始数据。这些模型依赖于假设粒子是球形的(或椭球体)，具有均匀的或简单的核壳组成。该项目将侧重于开发创新的基于激光的仪器，以更准确地描述气溶胶粒子的特性，特别是侧重于提高非球形粒子的测量精度。博士生将开发基于散射光的角度分布(通常称为散射相函数)来测量现场粒子形态的技术。最近才演示了现场气溶胶相函数的直接测量(见图1)，该项目将专注于利用这些新能力来产生与交通相关的PM排放的重要新数据集。2、3这些数据集将减少交通排放对心肺健康、对流层化学和辐射强迫的影响的不确定性。除了提高地面测量能力外，这一研究项目还将改进遥感测量的验证。地面和卫星辐射计的气溶胶数据产品依赖于将仪器相对于太阳的视角联系起来的算法，以确定颗粒的尺寸分布和辐射效应。散射相函数的不准确假设可能会导致气候模型、卫星和地面辐射计之间的一致性较差，尤其是在以非球形颗粒为特征的区域(例如沙漠和城市地区)。4.目标本项目的目标包括：1.开发新型基于激光的仪器，用于现场表征气溶胶颗粒的尺寸和形状；2.将仪器部署到路边空气质量监测点，以测量交通排放；3.将测量的光散射与模型和遥感反演中实施的算法进行比较；4.调查车辆类型和大气过程对交通颗粒物特征的影响。

Road traffic remains among the most significant sources of particulate matter (PM) pollution in the UK. With the decline in tailpipe emissions, non-exhaust sources - including resuspended road dust and tyre and brake friction - of PM are becoming increasingly important. Non-exhaust PM are now thought to dominate over exhaust sources.1 Factors that influence non-exhaust emissions are poorly understood, making it difficult to develop solutions for PM reductions and predict future changes as electric and hybrid vehicles become more popular. In addition, there is a great deal of uncertainty in the physical characteristics of these particles that determine climate and public health effects. Optical instruments have become popular for in situ measurements of atmospheric aerosol with high (~1 Hz) time resolution. In order to retrieve quantitative information on the particle size and refractive index, mathematical models are often required to invert raw data. These models rely on assumptions that the particles are spherical (or ellipsoids) with a homogeneous or simple core-shell composition. This project will focus on developing innovative laser-based instruments to more accurately characterise aerosol particle properties, specifically focusing on improving accuracy in measurements of non-spherical particles. The PhD candidate will develop techniques to measure particle morphology in the field based on the angular distribution of scattered light (commonly referred to as the scattering phase function). Direct measurements of aerosol phase function in the field have only recently been demonstrated (see Figure 1), and this project will focus on leveraging these new capabilities to produce vital new data sets on traffic related PM emissions.2,3 These data sets will reduce uncertainty in the effects of traffic emissions on cardiopulmonary health, tropospheric chemistry, and radiative forcing. In addition to improving ground-based measurement capabilities, this research project will also enable improved validation of remote sensing measurements. Aerosol data products from ground- and satellite-based radiometers rely on algorithms that relate the viewing angle of the instrument relative to the sun to determine the size distribution and radiative effects of the particles. Inaccurate assumptions of the scattering phase function may contribute to poor agreement between climate models, satellites, and ground-based radiometers, particularly in areas characterised by non-spherical particles (e.g. deserts and urban areas).4,5 Objectives The objectives of this project include: 1. Develop novel laser-based instrumentation to characterise aerosol particle size and shape in situ; 2. Deploy instrument to roadside air quality monitoring site to measure traffic emissions; 3. Compare measured light scattering with algorithms implemented in models and remote sensing retrievals; 4. Investigate the role of vehicle type and atmospheric processes on traffic particle characteristics.