Reactivity of Organic Radicals in the Atmospheric Aqueous Phase

在化学系环境化学科学项目的支持下，杰西·克罗尔和威廉·绿色教授将对大气中小液滴中活性化学物质的命运进行实验和建模研究。有机（含碳和氢）化合物从各种来源排放到大气中，包括车辆，野火和植物。这些化合物可能对空气质量和气候产生重大影响，因为它们在大气中发生化学反应，形成臭氧和细颗粒物等产品。许多这些反应发生在气相中，但有些发生在悬浮在空气中的液态水滴（云滴，雾滴和细颗粒）中。然而，水滴中发生的有机化学通常知之甚少。因此，本项目致力于液态水中有机自由基（有机氧化反应中的关键活性物质）的化学。实验室研究将涉及自由基的产生和反应产物的测量，计算研究将侧重于预测化学反应的速率和产物。研究生和本科生将参与这项研究，该团队将参加麻省理工学院范围内的研究机会计划，针对传统上代表性不足的群体的学生。 生成的软件将广泛提供。有机过氧（RO 2）和氧（RO）自由基将通过自由基前体的光解在水相中产生，从而允许控制它们的化学结构和浓度。将使用气溶胶质谱法和化学电离质谱法对产品进行真实的实时测量。这些自由基物种的产物已经得到了相当多的研究，尽管主要是在气相和本体有机相中。对气溶胶中这种自由基的化学性质的研究少得多，主要限于使用气相色谱法测量反应产物的脉冲辐解实验。最初的工作将集中在优化技术，以产生这些自由基。随后的化学研究将首先在本体水相中进行，然后在悬浮的亚微米液滴中进行。与此同时，计算工作（速率系数计算和化学动力学建模）预计将提供深入了解潜在的机制，并将有助于将结果推广到更广泛的反应和条件。水相自由基化学可能与气相中的自由基化学有很大不同：液态水的存在会显著影响基元反应的动力学和热力学，并引入气相中无法发生的新反应途径。潮解颗粒的独特化学环境引入了额外的化学效应，与气体-颗粒分配和高离子强度相关。这项工作将调查所有这些影响，通过实验室和计算研究的水相自由基化学，目的是提高我们的基本反应性，大气命运的理解，这些重要的自由基中间体的最终影响。这个奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

With support from the Environmental Chemical Sciences Program in the Division of Chemistry, Professors Jesse Kroll and William Green will pursue experimental and modeling studies of fate of reactive chemical species in small droplets in the atmosphere. Organic (carbon- and hydrogen-containing) compounds are emitted into the atmosphere from a wide range of sources, including vehicles, wildfires, and plants. These compounds can have major impacts on air quality and climate, because in the atmosphere they undergo chemical reactions, forming products that such as ozone and fine particle matter. Many of these reactions occur in the gas phase, but some occur within liquid water droplets suspended in the air (cloud droplets, fog droplets, and fine particles). However, the organic chemistry occurring in water droplets is generally poorly understood. Therefore, this project addresses the chemistry of organic radicals (key reactive species in organic oxidation reactions) within liquid water. Laboratory studies will involve the generation of radicals and measurements of their reaction products, and computational studies will focus on predicting rates and products of the chemical reactions. Graduate and undergraduate students will be involved in this research, and the team will participate in MIT-wide research opportunity programs aimed at students from traditionally underrepresented groups. The software generated will be made widely available. Organic peroxy (RO2) and oxy (RO) radicals will be generated in the aqueous phase by the photolysis of radical precursors, allowing for control of their chemical structure and concentration. Products will be measured in real time using aerosol mass spectrometry and chemical ionization mass spectrometry. The products of such radical species have received considerable study, though primarily in the gas phase and bulk organic phase. The chemistry of such radicals in aerosols has received substantially less study, mostly limited to pulse radiolysis experiments that used gas chromatography to measure reaction products. Initial work will focus on optimizing techniques to generate these radicals. Subsequent studies of the chemistry will be carried out first in the bulk aqueous phase and then within suspended submicron droplets. In parallel, computational work (rate coefficient calculations and chemical kinetic modeling) is expected to provide insight into underlying mechanisms and will help generalize results to a wider range of reactions and conditions. Aqueous-phase radical chemistry may be substantially different from that in the gas phase: the presence of liquid water can dramatically affect the kinetics and thermodynamics of elementary reactions, as well as introduce new reaction pathways that cannot occur in the gas phase. The unique chemical environment of deliquesced particles introduces additional chemical effects, associated with gas-particle partitioning and high ionic strengths. This work will investigate all these effects, via laboratory and computational studies of aqueous-phase radical chemistry, with the aim of improving our understanding of the fundamental reactivity, atmospheric fate, and ultimate impacts of these important radical intermediates.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.