Semisolidity and Reactivity of Atmospheric Organic Aerosol Particles

二次有机气溶胶（SOA）是通过气相或挥发性有机化合物（VOCs）的氧化、转化和冷凝在大气中形成的颗粒相。挥发性有机化合物的来源既可以是生物源的，也可以是人造的。最近的科学研究表明，一些SOA颗粒表现出固体的物理性质，而不是通常期望的气溶胶的液体性质。粘度可忽略不计的硬固体（10^12 Pa s）和高粘度（10^2 Pa s）的粘稠液体的中间行为在过渡范围内被观察到，这里称为半固体。分子在这种半固体中的扩散速度可能比在液体中慢几个数量级，但仍然足够快，可以发生反应化学。在这个项目中提出的一系列问题是调查性的，甚至是推测性的，旨在阐明半固态SOA的机械特性，气溶胶的单个（和批量）特性。第一个目标是量化半固态如何随相对湿度和SOA化学变化。第二个目标是测量化学反应性，包括气相反应物的损失和颗粒相产物的外观，如何随SOA半固态而变化。这项研究将广泛使用一个环境室，在这个环境室中挥发性有机化合物将被氧化。大气中有机半固体颗粒的出现可能对SOA颗粒的气体吸收和随后的化学老化产生重要影响，这反过来又与它们的气候强迫特性及其对公众健康的影响有关。

Secondary organic aerosols (SOA) are particulate phases that form in the atmosphere through oxidation, transformation and condensation of gas phase, or volatile organic compounds (VOCs). Source VOCs can be either biogenic or man-made compounds. Recent scientific investigations have demonstrated that some SOA particles exhibit the physical properties of a solid rather than those of liquids normally expected of aerosol. Intermediate behavior of a hard solid of negligible viscosity (10^12 Pa s) and a thick liquid of high viscosity (10^2 Pa s) is observed in a transitional range, herein termed semisolid. The diffusion of molecules in such a semisolid may be orders of magnitude slower than in a liquid, yet still fast enough that reactive chemistry can take place. The set of questions raised in this project are investigative, even speculative in nature, designed to shed light on the mechanical properties of semisolid SOA, individual (and bulk) properties of aerosols. A first objective is to quantify how semi-solidity varies with relative humidity and SOA chemistry. A second objective is to measure how chemical reactivity, including both the loss of gas-phase reactants and the appearance of particle-phase products, varies with SOA semi-solidity. The study will make extensive use of an environmental chamber in which VOCs will be oxidized.The atmospheric occurrence of organic semisolid particles may have important implications for gas uptake and subsequent chemical aging of SOA particles, which in turn are of interest to their climate forcing properties and their effects on public health.