How Do Particle Chemical Properties Affect Aerosol Chemical Reactions?

研究了以大气粒子为代表的有机分子的氧化动力学和氧化机理。总体目标是了解缩合相基质如何影响化学反应的产物、速率和机理。这些信息对于理解和量化大气粒子的老化过程至关重要。最近对大气颗粒中有机分子抵抗臭氧和羟基自由基攻击的寿命的研究导致了实验室研究和现场测量之间的差异，后者表明化学成分的寿命明显更长。这个项目的假设是矩阵效应是造成明显差异的原因。例如，假设将油酸掺入二次有机气溶胶（SOA）中，与气相臭氧反应缓慢，因为臭氧必须克服SOA基质中的扩散屏障才能到达油酸的活性双键。此外，反应机制和由此形成的产物被假设取决于反应基质的性质。要进行的实验需要产生不同基质组成的气溶胶颗粒，并加入活性有机分子作为次要成分。为此，将在新的哈佛烟雾室中生成几种组合的SOA，并将目标有机分子纳入SOA中。将产生不同扩散率、粘度和酸度的SOA。无机基质对种子颗粒组成的影响也将通过硫酸铵、硝酸铵和氯化钠的变化来探讨。在所有情况下，将通过改变相对湿度来分析含水量的作用。反应性有机分子包括油酸、油酸甲酯、亚油酸、异丙酸、石油硒酸及其铵盐。实验将采用新获得的Aerodyne飞行时间气溶胶质谱仪（TOF-AMS）作为臭氧分解过程中活性有机分子的实时监测。还将收集颗粒，用于色谱法的离线产品分析。这项工作将提供关于大气气溶胶的重要信息，这将提高我们对云成核特性的基本理解，以及颗粒物对健康的潜在影响。该奖项将为研究生和本科生提供培训机会。

The oxidation kinetics and mechanisms of organic molecules incorporated as minor constituents inside particles representative of atmospheric particles will be studied. The overall goal is to understand how the condensed-phase matrix affects the products, rates, and mechanisms of chemical reactions. This information is essential to understanding and quantifying the aging processes of atmospheric particles.Recent studies of lifetimes of organic molecules in atmospheric particles against attack by ozone and hydroxyl radical have resulted in a discrepancy between laboratory studies and field measurements, the latter indicating significantly longer lifetimes of the chemical constituents. The hypothesis of this project is that matrix effects are responsible for the apparent discrepancies. Oleic acid incorporated in secondary organic aerosol (SOA) is, for example, hypothesized to react slowly with gas phase ozone because the ozone must overcome a diffusion barrier in the SOA matrix to reach the reactive double bonds of oleic acid. Moreover, the reaction mechanisms and hence products formed are hypothesized to depend on the nature of the reaction matrix.The experiments to be conducted require the generation of aerosol particles of different matrix compositions and the incorporation of reactive organic molecules as minor constituents. For this purpose, SOA of several compositions will be generated in the new Harvard Smog Chamber, and target organic molecules will be incorporated in the SOA. SOA of different diffusivity, viscosity and acidity will be produced. The effect of inorganic matrices will also be explored by variation of seed particle composition among ammonium sulfate, ammonium nitrate, and sodium chloride. In all cases, the role of water content will be analyzed by varying relative humidity. The reactive organic molecules will include oleic acid, methyl oleate, linoleic acid, vaccenic acid, petroselinic acid, and their ammonium salts. The experiments will employ a newly acquired Aerodyne Time-of-Flight Aerosol Mass Spectrometer (TOF-AMS) as a real-time monitor of the reactive organic molecules during ozonolysis. Particles will also be collected for off-line product analysis by chromatography.This work will provide important information on atmospheric aerosols that will improve our basic understanding of cloud nucleating properties, as well as potential health effects of particulate matter. The award will provide training opportunities for graduate and undergraduate students.