RUI: Gas and Aerosol Phase Chemistry of Multi-Generation Isoprene Oxidation Products

挥发性有机化合物（VOCs）的大气氧化影响对流层臭氧和二次有机气溶胶（SOA）的产生，对人类健康和全球气候产生影响。植物释放的异戊二烯是许多环境中的主要VOC。然而，异戊二烯形成臭氧和SOA的潜力仍然不确定。模拟臭氧生产异戊二烯是高度敏感的氮氧化物（NOx）的不确定的机械表示。此外，“自下而上”的异戊二烯排放数据和化学机制的基础上的计算低估了SOA浓度在异戊二烯为主的环境。这些认识上的差距限制了空气污染和气候模型的准确性。虽然OH自由基攻击异戊二烯后的初始反应已经得到了相当好的表征，但这些第一代产品的后续化学加工（也称为多代步骤）的研究却少得多，并且许多所需的关键动力学参数定量预测尚未得到表征。该项目将研究多代异戊二烯氧化产物的气相和颗粒相化学。具体地，将评价（a）作为OH +异戊二烯的第一代产物形成的有机硝酸酯的OH自由基引发的反应的动力学和产物，（B）由OH +异戊二烯形成的二羟基环氧化物的OH自由基引发的反应的动力学和产物，（c）OH +异丁烯醛的产物，包括H原子提取/OH加成分支比，和（d）2-甲基甘油酸和2-硝酸根合-2-甲基甘油酸（先前确定为异戊二烯衍生的第二有机气溶胶的组分）的酯化动力学，以及逆水解反应的酯化动力学。气相实验将利用湍流化学电离质谱技术，该技术允许独立控制OH和NOx水平。颗粒相实验将利用本体溶液/核磁共振技术和气溶胶室/气溶胶洗涤/核磁共振技术，这项研究工作的结果将有助于提高目前对大气化学的预测能力，从而促进就区域空气污染和气候变化的缓解战略作出知情的公共政策决定。该项目还将促进国家科学事业所需人力资源的开发。本科生直接参与原创研究将有助于他们为未来的科学职业做好准备，并有助于奥伯林学院科学经验的跨学科性质。该项目将在一个在本科科学教育和研究领域处于全国领先地位的机构进行，该机构一直致力于增加科学领域代表性不足的学生人数。

The atmospheric oxidation of volatile organic compounds (VOCs) influences the production of tropospheric ozone and secondary organic aerosol (SOA) with consequences for human health and global climate. Isoprene emitted by vegetation is the dominant VOC in many environments. However, both the ozone- and SOA-forming potential of isoprene remains uncertain. Modeled ozone production from isoprene is highly sensitive to the uncertain mechanistic representation of nitrogen oxides (NOx). In addition, "bottom-up" calculations based on isoprene emission data and chemical mechanisms underestimate SOA concentrations in isoprene-dominated environments. These gaps in understanding constrain the accuracy of air pollution and climate models. While the initial set of reactions that follow the OH radical attack on isoprene have been reasonably well characterized, the subsequent chemical processing of these first generation products (also known multi-generation steps) have received considerably less study and many of the key kinetics parameters that are required for quantitative prediction have not been characterized. This project will investigate the gas- and particulate-phase chemistry of the multi-generation isoprene oxidation products. Specifically, it will evaluate (a) the kinetics and products of the OH radical-initiated reactions of the organic nitrates formed as first-generation products of OH + isoprene, (b) kinetics and products of the OH radical-initiated reactions of dihydroxy-epoxides formed from OH + isoprene, (c) products of OH + methacrolein, including the H-atom abstraction/OH addition branching ratio, and (d) the esterification kinetics of 2-methylglyceric acid and 2-nitrato-2-methylglyceric acid (previously identified as components of isoprene-derived secondary organic aerosol), and of the reverse hydrolysis reaction. The gas-phase experiments will utilize the turbulent flow chemical ionization mass spectrometry technique, which allows OH and NOx levels to be controlled independently. The particulate-phase experiments will utilize bulk solution/NMR and aerosol chamber/aerosol scrubbing/NMR techniques.Results of this research effort will help improve current predictive capabilities for atmospheric chemistry and thereby facilitate informed public policy decisions regarding mitigation strategies for regional air pollution and climate change. This project will also contribute towards the development of the human resources necessary for the nation's scientific enterprise. The direct involvement of undergraduate students in original research will help prepare them for future careers in science as well as contribute to the increasingly interdisciplinary nature of the science experience at Oberlin College. The project will take place at an institution that is a national leader in the area of undergraduate science education and research and that has had an enduring commitment to increasing the number of underrepresented students in the sciences.