Improved measurements of soot using new particle morphology models

气溶胶（包括“烟灰”）对气候的影响很大，但也有很大的不确定性。如果不能减少对气候有影响的排放，可能会迫使人类在大气中分散光散射粒子，以防止失控的全球变暖。要进行这种“地球工程”，就需要对气溶胶在气候中的作用有一个精确的认识。****颗粒是造成与空气污染有关的死亡的最大因素，发动机产生的黑碳可能毒性特别大，但尚不清楚颗粒的哪种化学或物理特性会导致这种毒性。许多设备的颗粒排放受到管制，这些规定可能会变得更加复杂，对排放测量设备提出新的要求。粒子结构使这些测量复杂化。****气溶胶仪器对非球形气溶胶的响应方式取决于测量原理（质量、迁移率、停止距离、光散射、吸收、计数），粒子形态和材料特性影响测量结果。几十年来，聚集的气溶胶（如烟灰）被建模为由直径为dp的“初级颗粒”组成的分形，分形维数为Df~1.8。粒子之间的接触和短程构型在“分形前因子”kF中被捕获。这个3参数几何模型是一个非常有用的近似值，但可能已经走得太远了。研究人员长期以来观察到（基于透射电镜）初级颗粒没有统一的大小，但大小的变化被认为是随机分布在气溶胶种群中。最近，我们首次展示了原生粒度随骨料粒度的系统趋势。实际上，来自真实燃烧系统的烟尘是一种近似理想的分形聚集体的“外部混合物”，其原始颗粒直径非常不同。这些变化可能很重要，因为重要的气溶胶物理特性通常是主要颗粒直径的非线性函数：在模式中使用单一平均主要颗粒直径将导致对物理特性的不正确预测（或气溶胶测量值的不正确反演）。挑战在于开发一个能够捕捉关键变化的简单模型——这是拟议研究的核心目标。我们计划使用我们广泛的TEM图像数据库，并通过SMPS， CPMA，光散射和吸收测量进行相应的测量。****更好的结构模型为粒子形成的物理过程打开了一扇新的窗口。燃烧条件和颗粒形态之间的关系将在两个受控实验活动（一个模型气体火炬和一个光学发动机）中进行研究，并通过一个新的颗粒形成模拟来解释。建议拨款将利用其他拨款资助3个高质素的博士项目。**

The effect of aerosols (including "soot") on climate is large but also has a large uncertainty.  Failure to reduce climate-active emissions may force humanity to disperse light-scattering particles in the atmosphere to prevent runaway global warming. A precise knowledge of the role of aerosols in climate will be needed to do this "geoengineering".****Particles are the largest contributors to air-pollution-related deaths, and black carbon from engines may be particularly toxic, but it is not known which chemical or physical characteristics of particles cause this toxicity. Particle emissions from many devices are regulated and the regulations may become more sophisticated, placing new requirements on emission measurement equipment. Particle structure complicates these measurements.****Aerosol instruments respond to non-spherical aerosols in different ways depending on the measurement principle (mass, mobility, stopping distance, light scattering, absorption, count), and the particle morphology as well as material properties affect the measurement. For decades, aggregate aerosols (such as soot) have been modeled as fractals composed of "primary particles" of diameter dp, with a fractal dimension of Df~1.8. The contact between particles and short range configuration is captured in the "fractal prefactor" kF. This 3-parameter geometric model has been a very useful approximation but may have been taken as far as it can go. Researchers have long observed (based on TEM) that primary particles do not have a uniform size but the size variations were assumed to be randomly dispersed through the aerosol population. Recently we have shown, for the first time,  systematic trends of primary particle size with aggregate size. Effectively, the soot from real combustion systems is an "external mixture" of nearly ideal fractal aggregates with very different primary particle diameters. These variations can be important because the important aerosol physical characteristics are typically non-linear functions of primary particle diameter: the use of a single average primary particle diameter in models will result in an incorrect prediction of physical properties (or incorrect inversion of aerosol measurements). The challenge is to develop a simple model that can capture key variations - the core objective of the proposed research. We plan to do this using our extensive TEM image database with corresponding measurements by SMPS, CPMA, light scattering and absorption measurements.****A better model of structure opens a new window onto the physical processes of particle formation. The relation between combustion conditions and the particle morphology will be studied in two controlled experimental campaigns (a model gas flare and and an optical engine) and interpreted through a new simulation of particle formation.  The proposed funding will leverage other funding to support 3 high-quality PhD projects.**