Collaborative Research: Heterogeneous Photocatalytic Transformation of Isoprene: Relevance to Secondary Organic Aerosol Formation

本项目拟检验的假设是，大气中异戊二烯的多相光催化作用可能在二次有机气溶胶(SOA)的形成中起重要作用。将调查过渡金属颗粒半导体在异戊二烯光化学氧化为低挥发性产品过程中的大气相关性。光催化剂将包括与大气相关的过渡金属氧化物颗粒、沙漠沙和火山灰，尺寸在0.1至10微米之间。液-固光催化反应将从有机底物(异戊二烯和异戊二烯气相光化学氧化的初级产物、甲基丙烯醛和甲基乙烯基酮)、牺牲电子供体的存在(例如醋酸酯)、氧气浓度和pH等方面进行研究。将研究异戊二烯(一种二烯)和一系列相关的亲双烯化合物之间发生光化学Diels-Alder反应的可能性，然后分析低聚产物。这项研究将由加州理工学院和橡树冠科学研究所的高级研究人员监督。这些研究将通过指导未来的雾霾室内研究、识别异质光氧化途径的化学标记以及调查聚合产物，潜在地推动气溶胶研究领域的发展，这些聚合产物可能占到SOA质量的很大一部分。这项研究将由一名博士后学者和一名加州理工大学的研究生，以及社区大学生和高中教师通过橡树冠与高中生组成团队进行。这些努力将有助于扩大代表人数不足的群体对科学研究的参与。

The hypothesis to be tested in this project is that atmospheric heterogeneous photocatalysis of isoprene may play an important role in secondary organic aerosol (SOA) formation. The atmospheric relevance of transition metal-based particulate semiconductors in the photochemical oxidation of isoprene to low volatility products will be investigated. Photocatalysts will include atmospherically-relevant transition metal oxide particles, desert sand, and volcanic ash in the 0.1 to 10 micrometer size range. Liquid-solid photocatalytic reactions will be studied in terms of the organic substrate (isoprene and the primary products of isoprene gas-phase photochemical oxidation, methacrolein and methyl vinyl ketone), the presence of a sacrificial electron donor (e.g., acetate), oxygen concentration, and pH. The potential for photochemical Diels-Alder reactions to occur between isoprene (a diene) and a range of relevant dienophiles will be investigated, followed by analysis for oligomeric products. The research will be overseen by senior investigators from CalTech and the Oak Crest Institute of Science.These studies will potentially advance the field of aerosol research by guiding future smog chamber studies; identifying chemical markers characteristic of heterogeneous photooxidation pathways; and investigating the polymerization products, which may account for a significant portion of the SOA mass. The research will be carried out by a post-doctoral scholar, and a graduate student at Caltech, as well as community college students and high school teachers working in teams with high school students via Oak Crest. These efforts will help to broaden the participation of underrepresented groups in scientific research.