CAREER: Photochemical Aging of Atmospheric Organic Aerosol: Chamber Studies of the Chemical Evolution of Oxidized Organic Species

该项目通过实验室研究氧化有机物的光化学老化来研究有机气溶胶(OA)的化学演化。光化学老化被定义为粒子在几天的大气氧化过程中经历的质量和组成的变化，在实验室对OA形成的研究中通常不能准确地模拟。这在很大程度上是由于实验时间尺度的限制，或将实验条件外推到大气条件。在这个项目中，老化研究将在环境舱中进行，允许气体-颗粒分配和其他关键过程发生的程度与大气中类似，但氧化剂浓度升高和持续，因此可以接触到更长时间的氧化剂暴露。计划中的实验的重点是低挥发性、多功能、氧化物种的化学，这些物种在OA中占很大比例。由这种氧化有机物(单一模型化合物或更复杂的混合物)组成的颗粒将被引入室内，并暴露在高浓度的羟基(OH)自由基中。有机气溶胶的光化学老化有三种不同的途径：凝聚相有机物的非均相氧化、半挥发性有机物的气相氧化和水溶物的水相氧化。测量颗粒大小和组成作为OH暴露的函数，将允许确定OA的质量和氧化程度的变化，以及这些反应的动力学。这类研究的结果可用于直接为旨在模拟氧化老化时大气酸化变化的模型提供信息。广泛影响：这项研究的结果将为有关气溶胶-气候和气溶胶/健康相互作用的政策提供信息。此外，该项目的教育部分旨在通过在当地一所公立学校实施一项新的教育方案，让本科生参与实验室研究和研究生培训，促进各级学生的科学发展。将在罗克斯伯里(波士顿一个经济困难的社区)的一所K-8学校制定并实施一项针对6-8年级学生的外展计划，重点是“天气和污染”。这将建立在现有的针对中学生的成功外联计划的基础上，在该计划中，首席调查员(PI)小组的成员开发并运营了学校的第一个科学博览会计划，以及一个课外科学俱乐部。该计划最初将作为单一学校试点计划实施，目标是通过教师培训扩展到波士顿公立学校系统中的其他学校。这项工作还将促进本科生和研究生的教育。本科生将通过麻省理工学院的本科生研究机会计划(面向麻省理工学院学生)和麻省理工学院的暑期研究计划(针对来自其他大学传统上代表性较低的群体的学生)直接参与研究，PI是该计划的导师。拟议中的研究将占研究生博士培训的很大一部分，研究生还将通过在推广项目中扮演主要角色并为本科生(S)提供建议来获得教育经验。这项研究的结果将被纳入PI的本科生和研究生课堂教学。

This project addresses the chemical evolution of organic aerosol (OA) through laboratory studies of the photochemical aging of oxidized organics. Photochemical aging, defined as the changes in mass and composition that particles undergo over several days of atmospheric oxidation, is generally not simulated accurately in laboratory studies of OA formation. This is largely due to limitations in experimental timescales or extrapolation of experimental conditions to those of the atmosphere. In this project, aging studies will be carried out in an environmental chamber, allowing for gas-particle partitioning and other key processes to occur to a similar extent as in the atmosphere, but with elevated and sustained oxidant concentrations, so that longer oxidant exposures can be accessed. The focus of the planned experiments is the chemistry of low-volatility, multifunctional, oxidized species, which make up a large fraction of OA. Particles made up of such oxidized organics (either single model compounds or more complex mixtures) will be introduced into the chamber and exposed to high concentrations of hydroxyl (OH) radicals. Three different pathways by which organic aerosol may be photochemically aged will be investigated: heterogeneous oxidation of condensed-phase organics, gas-phase oxidation of semivolatile species, and aqueous-phase oxidation of water-soluble species. Measurements of particle size and composition as a function of OH exposure will allow for the determination of the changes to mass and degree of oxidation of the OA, as well as of the kinetics of these reactions. Results from such studies can be used to directly inform models aimed at simulating changes to atmospheric OA upon oxidative aging.Broader Impacts: The results of this research will inform policy on aerosol-climate and aerosol/health interactions. Additionally, the educational component of this project aims to promote the scientific development of students spanning a range of levels, by implementation of a new education program at a local public school, the engagement of undergraduates in laboratory research, and the training of graduate students. An outreach program focused on "Weather and Pollution" for 6th-8th graders will be developed and implemented at a K-8 school in Roxbury (an economically disadvantaged neighborhood of Boston). This will build upon an existing successful outreach program to middle school students, in which members of the Principal Investigator's (PI) group developed and ran the school's first science fair program, as well as an after-school science club. This program will originally be implemented as a single-school pilot program, with the goal of expansion to other schools in the Boston Public School system via teacher training. This work will also promote education at the undergraduate and graduate level. Undergraduate students will be directly involved in the research, via MIT's Undergraduate Research Opportunity Program (for MIT students) and MIT's Summer Research Program (aimed at students from traditionally underrepresented groups from other colleges), for which the PI is a mentor. The proposed research will represent a large fraction of a graduate student's Ph.D. training, and the graduate student will also gain educational experience by playing a major role in the outreach program and advising the undergraduate student(s). Results from the research will be incorporated into the PI's undergraduate- and graduate-level classroom teaching.