Carbon nanoparticle structure: implications for environmental impacts, measurement and formation

含碳燃料的燃烧通常会产生碳质纳米颗粒--“碳烟”或“黑碳”，通常是直径为dp~15-40纳米的“初级颗粒”的分形聚集体。柴油发动机、森林火灾或工业过程中产生的烟尘是每年500万至900万空气污染死亡的主要贡献者，也是主要的气候变暖因素。另一方面，故意生产的“黑碳”是最早的纳米结构材料之一，是用于传感器、催化剂载体和能源系统的一系列新材料的一部分，也可能是一种燃料脱碳的途径。碳纳米颗粒的行为取决于颗粒的结构，特征是初级颗粒的尺寸分布、聚集体结构和碳的亚纳米准化学排列(例如，石墨区的大小)。根据这种结构，可以预测这些颗粒将如何与光线相互作用，如何在肺部沉积，或如何被收集在气体清洁设备中。煤烟形成的主流模型是，首先形成初级颗粒，然后布朗凝聚产生包含初级颗粒的聚集体，这些初级颗粒来自燃烧系统的许多部分。我的团队已经取得了一项发现，导致了对这一模型的重大更新，这是这项提案的重点。我们所发现的是，对于大多数燃烧系统，每个烟尘聚集体在其在燃烧室中形成的时间与其被排放到大气中的时间之间并不与其他烟尘颗粒相互作用。因此，排放的烟尘聚集体携带关于装置中燃烧条件的分布的信息，在材料特性和形态上不同。例如，平均而言，大小不同的聚集体似乎来自火焰的不同部分，并且具有不同的初级颗粒尺寸和不同的石墨化程度。由于烟尘颗粒是碳烟初级颗粒大小和性质在聚集体中是一致的，但在聚集体之间非常不同，这种新的碳烟结构模型被称为外部混合假说(EMH)。在接下来的5年里，我的团队将通过开发更好的图像处理方法(需要获得高分辨率的烟尘结构信息)、气溶胶动力学模型(需要将排气后条件与火焰中的条件联系起来)和更好的烟尘测量方法(利用EMH为我们提供了比以前可用的更准确的烟尘结构表示)来探索EMH。这些都是实现定量了解烟尘形成的长期愿景的重要步骤，并开发能够支持环境监测、环境科学和工程纳米颗粒合成的气溶胶测量方法-这些领域不仅将使用这项研究，还将为这里培训的HQP(3名本科生，3名)提供职业机会1名硕士研究生和2名博士生)。

Combustion of carbon-containing fuels often results in carbonaceous nanoparticles - "soot" or "black carbon", typically fractal aggregates of "primary particles" with diameter dp~15-40 nanometers. Soot produced in diesel engines, forest fires, or industrial processes is a major contributor to 5-9 million air pollution deaths annually, and a major climate-warming agent. On the other hand, intentionally produced "black carbon" was one of the first nanostructured materials, part of a family of new materials used for sensors, catalyst supports, and energy systems, and possibly a route to fuel decarbonization.  The behavior of carbon nanoparticles depends on structure of the particles, characterized by the size distribution of the primary particles, the aggregate structure, and the sub-nanometer quasi-chemical arrangement of carbon (eg, size of graphitic domains). Given this structure, it is possible to predict how these particles will interact with light, deposit in lungs, or be collected in gas cleaning devices. The prevailing model for soot formation is that first, primary particles form, then Brownian coagulation produces aggregates containing primary particles drawn from many parts of the combustion system. My team has made a discovery resulting in a significant update to this model, the focus of this proposal. What we have found is that for most combustion systems, each soot aggregate does not interact with other soot particles between the time it is formed in a combustion chamber and the time that it is emitted to the atmosphere.  As a result, the emitted soot aggregates carry information about the distribution of combustion conditions in the device, differing in material properties and morphology.  For example, on average, large and small aggregates appear to come from different parts of the flame, and have different primary particle size and different degrees of graphitization.  Because the soot particles are soot primary particle sizes and properties are uniform within aggregates but very different between aggregates, this new structural model of soot is called the External Mixing Hypothesis (EMH). Over the next 5 years my team will explore the EMH through development of better image processing methods (needed to obtain high-resolution soot structural information), aerosol dynamics models (needed to connect post-exhaust conditions to in-flame conditions) and better soot measurement methods (capitalizing on the EMH which provides us with a much more accurate representation of soot structure than previously available).  These are important steps towards a long term vision of understanding soot formation quantitatively and developing aerosol measurement methods that can support environmental monitoring, environmental science, and engineered nanoparticle synthesis- the fields that will not only use this research but provide career opportunities for the HQP trained here (3 undergraduates, 1 MASc student, and 2 PhD students).