Atmospheric Chemistry of Methylated Selenium Compounds and Physicochemical Properties of the Resulting Aerosols

本项目涉及大气硒的命运和分布的研究。环境室将用于量化含硒有机化合物产生的二次有机气溶胶，并使用一套在线和离线仪器确定产生的主要气体和气溶胶产品。从该项目获得的结果将提高对长期接触有机硒化合物的理解，特别是在美国西部农业山谷等富硒土壤和沉积物地区，可能会对公众健康产生负面影响。系统研究几种甲基化硒化合物在不同氮氧化物水平下的气相和水相氧化，使用不同的氧化剂（OH， NO3和O3）和氧化时间尺度。本研究的目的是进一步了解由选定甲基化硒的气相和水相氧化形成的二次气溶胶，并提高对由此产生的气溶胶的化学和微物理性质的认识，这些气溶胶控制对人类健康和环境化学的影响。假设包括：(1)所选有机硒化合物的光氧化和硝酸盐自由基氧化导致了显著的二次气溶胶形成，且形成量依赖于nox；在高NOx存在下，硝酸盐氧化途径的产率与光氧化途径相似；(2)长氧化时间导致产品的显著破碎，因此减少了二次气溶胶质量；(3)低NOx条件下甲基化Se中间氧化产物的水相氧化导致含Se的二次气溶胶种的形成和氢过氧化物浓度的升高，从而导致活性氧的产生增加。这项工作包括培训和指导几名研究生和本科生，并包括在当地高中和初中开展外联和教育活动。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。

This project involves the study of the fate and distribution of atmospheric selenium (Se). An environmental chamber will be used to quantify the formation of secondary organic aerosol from selenium (Se)-containing organic compounds and determine the major gas and aerosol products generated using a suite of online and offline instrumentation. The results obtained from this project will improve the understanding of how long-term exposure to organic Se compounds, especially in areas with Se-rich soils and sediments such as agricultural valleys in the western US, might negatively influence public health.Systematic studies of gas and aqueous phase oxidation of several methylated Se compounds will be conducted under variable nitrogen oxide levels using various oxidants (OH, NO3 and O3) and oxidation time scales. The objectives of this research are to develop an improved understanding of secondary aerosol formation from gas and aqueous phase oxidation of selected methylated Se species and improve knowledge about the chemical and microphysical properties of the resulting aerosols that control the impacts on human health and environmental chemistry. The hypotheses include the following: (1) Photooxidation and nitrate radical oxidation of the selected organoselenium compounds lead to significant secondary aerosol formation and the formation yields are NOx-dependent; The yield of the nitrate oxidation pathway is expected to be like that of photooxidation in the presence of high NOx; (2) Long oxidation times lead to significant fragmentation of the products and, therefore, a reduction in secondary aerosol mass; and (3) Aqueous phase oxidation of methylated Se intermediate oxidation products under low NOx conditions leads to formation of Se-containing secondary aerosol species and a higher concentration of hydroperoxides, which results in the increased production of reactive oxygen species.This effort involves the training and mentoring of several graduate and undergraduate students and includes outreach and educational activities at local high schools and middle schools.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.