Collaborative Research: Humidity and Temperature Effects on Phase Separation and Particle Morphology in Internally Mixed Organic-Inorganic Aerosol

在美国国家科学基金会化学部环境化学科学项目的支持下，加州大学河滨分校（UCR）的James Davies和三一大学的Ryan Davis将研究环境条件下有机-无机混合气溶胶颗粒的相态。气溶胶影响气候，因为它们构成云的基础，并参与散射和吸收阳光。气溶胶还会对空气质量产生负面影响，并为空气传播疾病提供媒介。与气溶胶有关的具体环境影响取决于气溶胶颗粒的化学成分和相态。对有机-无机气溶胶（例如在环境中发现的气溶胶）的相态认识不足，是气候和空气质量模型不确定的一个来源。有机-无机混合粒子可以根据环境条件形成一系列相态；这些包括液相和固相，以及无定形相，如粘性液体、玻璃和凝胶。该项目将探索气溶胶颗粒中非晶态的形成，并描述决定其对环境影响的特性。加州大学河滨分校和三一大学之间的合作将促进两所大学的本科生和研究生研究，并寻求在一系列科学学科中提高对气溶胶化学的理解。为了提高对环境中气溶胶颗粒的认识，该项目是R1公立大学UC-Riverside （James Davies研究小组）和以本科生为主的文科和理科大学Trinity university （Ryan Davis研究小组）的团队之间的合作研究，将研究温度和相对湿度对内部混合有机-无机气溶胶颗粒的相态和相关特性的作用。由于吸湿性相互作用，含有有机和无机化合物混合物的气溶胶颗粒在相对湿度（RH）和温度变化的响应中表现出复杂的相行为。气溶胶颗粒的相形态影响它们与光的相互作用，它们对化学过程的响应，由于粘度的变化，以及它们的冰和云的成核势。本提案将研究暴露于受控RH和温度条件下的内部混合有机-无机气溶胶颗粒的相形态和相关流变特性。主要目标是：(1)系统地表征含有大气相关盐和含氧有机物的颗粒的吸湿性和粘度；(2)确定相分离开始的温度和湿度条件，并与分子组成相关联；(3)探讨粘度和相分离对分子扩散速率的影响。为了实现这些目标，含水含氧有机化合物的单个颗粒和与大气相关的一价和二价盐将使用电动平衡悬浮。光谱学、显微镜和光散射方法将用于鉴定相分离，而新的和已建立的表征方法将用于测量吸湿生长、粘度和扩散输运。这项研究将有助于激励下一代科学家，让本科生和研究生的研究人员在一个与气候科学研究更广泛相关的项目中，对气溶胶进行严格的物理研究和表征。气候科学研究是当今社会非常感兴趣和重要的领域。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With support from the Environmental Chemical Sciences Program in the Division of Chemistry at NSF, James Davies of the University of California-Riverside (UCR) and Ryan Davis of Trinity University will study the phase state of mixed organic-inorganic aerosol particles under environmental conditions. Aerosols influence climate as they form the basis of clouds and are engaged in both the scattering and the absorption of sunlight. Aerosols can also negatively affect air quality and provide a vehicle for the spread of airborne disease. The specific environmental impact associated with aerosols depends upon the chemical composition and phase state of the aerosol particles. Inadequate knowledge of the phase state of organic-inorganic aerosols, such as those found in the environment, represents a source of uncertainty in climate and air quality models. Mixed organic-inorganic particles can form a range of phase states depending on environmental conditions; these include liquid and solid phases, and amorphous phases, such as viscous liquids, glasses, and gels. This project will explore the formation of amorphous phase states in aerosol particles and characterizes the properties that determine their impacts in the environment. This collaboration between UC Riverside and Trinity University will facilitate undergraduate and graduate research across both institutions and seeks to provide for an improved understanding of aerosol chemistry across a range of scientific disciplines.To enhance knowledge of aerosol particles in the environment, this project is a collaborative study between teams at an R1 public university, UC-Riverside--the James Davies research group--and at a predominantly undergraduate liberal arts and sciences university, Trinity University--the Ryan Davis research group--will examine the role of temperature and relative humidity on the phase state and associated properties of internally mixed organic-inorganic aerosol particles. Aerosol particles containing mixtures of organic and inorganic compounds exhibit complex phase behavior in response to changes in relative humidity (RH) and temperature due to hygroscopic interactions. The phase morphology of aerosol particles influences their interactions with light, their response to chemical processing due to changes in viscosity, and their ice and cloud nucleating potential. This proposal will investigate the phase morphology and associated rheological properties of internally mixed organic-inorganic aerosol particles exposed to controlled RH and temperature conditions. The main objectives are: (1) systematically characterize the hygroscopicity and viscosity of particles containing atmospherically-relevant salts and oxygenated organics; (2) determine the temperature and humidity conditions for the onset of phase separation and correlate with molecular composition; and (3) explore the consequences of viscosity and phase separation on the rate of molecular diffusion. To achieve these goals, single particles of aqueous oxygenated organic compounds and atmospherically-relevant mono- and divalent salts will be levitated using an electrodynamic balance. Optical spectroscopy, microscopy and light scattering methods will be used to identify phase separation while new and established characterization methods will be applied to measure hygroscopic growth, viscosity, and diffusive transport. The research will help to motivate the next generation of scientists by exposing undergraduate and graduate researchers to the physically rigorous study and characterization of aerosols in a project that relates more generally to climate science research, an area of great societal interest and importance today.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.