Organic Aerosol Dynamics: Molecular Interactions, Single Particles and Modest Driving Forces

细颗粒物在大气化学中起着关键作用，影响着人类健康和天气。细颗粒的物理和化学性质是控制其行为的关键。这些颗粒的性质与液体或固体有很大的不同。典型的颗粒直径约为300纳米，包含大约1000万个单个分子。这些分子中有一半以上是有机（含碳）化合物，甚至一个粒子往往包含数十万种不同的有机分子，其中大多数从未被化学家分离或合成过。这些有机分子附着在微小的颗粒上，而不是离开颗粒，漂浮（挥发）到空气中。有些有机化合物类似于沥青或复合糖。这项研究促进了对与能源生产有关的燃烧过程和产品如何影响人类健康的基本理解。卡内基梅隆大学的Neil Donahue教授和他的研究生研究了许多模型系统的行为，使用复杂的质谱仪，可以测量单个300纳米粒子的组成，以及互补的化学电离质谱仪，可以测量气体和粒子相中的单个分子。他们制造出与大气中氧化程度逐渐升高的有机颗粒相似的有机颗粒，通过直接测试半挥发性有机物是否能扩散到颗粒中，以及两种最初不同的具有半挥发性成分的颗粒是否因混合而相互演化，来观察颗粒是否变得更粘稠。研究人员在相对湿度条件下进行了这些实验，因为大气中的湿度变化很大，而且众所周知，湿颗粒的粘性要小得多，扩散性更强。通过与西北大学的同事合作，他们使用含有稳定碳同位素13C的合成分子，使用质谱法从不同的粒子群中干净地分离分子。该项目为博士生的研究生涯做准备。多纳休教授是美国国家科学院创立的科学与工程大使项目的大使。他把重点放在能源使用和环境健康问题之间的耦合。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。

Fine particles play a key role in atmospheric chemistry, and effect human health and weather. The physical and chemical properties of fine particles are critical in controlling their behavior. The properties of these particles are significantly different from liquids or solids. Typical particles are about 300 nanometers in diameter and contain roughly 10 million individual molecules. Well over half of those molecules are organic (carbon containing) compounds, and even a single particle often contains hundreds of thousands of different organic molecules, most of which have never been isolated or synthesized by chemists. These organic molecules stick to the tiny particles rather than letting go of the particle and floating (volatilizing) into the air. Some of the organic compounds resemble asphalt or complex sugars. This research advances fundamental understanding of how combustion processes and products related to energy production may influence human health. Professor Neil Donahue and his graduate students at Carnegie Mellon University study the behavior of a number of model systems using sophisticated mass spectrometers that can measure the composition of individual 300 nm particles along with complementary chemical ionization mass spectrometers that can measure individual molecules in the gas and particle phases. They generate organic particles mimicking those found in the atmosphere with progressively higher degrees of oxidation to see if the particles become more viscous in a way that matters - by directly testing if semi-volatile organics can diffuse into the particles and whether two initially distinct populations of particles with semi-volatile constituents evolve toward each other because of mixing. The researchers conduct these experiments over a wide range of relative humidity conditions as humidity varies widely in the atmosphere and because wet particles are known to be much less viscous and more diffusive. Via a collaboration with colleagues at Northwestern University, they use synthesized molecules containing the stable carbon isotope, 13C, to cleanly separate molecules from different particle populations using mass spectrometry. The project prepares doctoral students for a research career. Professor Donahue is an ambassador in the Science and Engineering Ambassadors Program founded by the National Academies. He brings a focus on the coupling between energy use and environmental health issues.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.