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

本项目通过对氧化有机物光化学老化的实验室研究来解决有机气溶胶（OA）的化学演化问题。光化学老化被定义为粒子在数天的大气氧化中所经历的质量和成分的变化，在OA形成的实验室研究中通常无法准确模拟。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的限制。在这个项目中，老化研究将在一个环境室中进行，允许气体-颗粒分裂和其他关键过程发生在与大气相似的程度，但具有升高和持续的氧化剂浓度，因此可以访问更长时间的氧化剂暴露。计划实验的重点是低挥发性、多功能、氧化物质的化学性质，这些物质占OA的很大一部分。由这些氧化有机物组成的颗粒（无论是单一模型化合物还是更复杂的混合物）将被引入腔室并暴露于高浓度的羟基（OH）自由基中。有机气溶胶光化学老化的三种不同途径将被研究：冷凝相有机物的非均相氧化，半挥发性物质的气相氧化和水溶性物质的水相氧化。测量颗粒大小和组成作为氢氧根暴露的函数，可以确定氢氧根质量和氧化程度的变化，以及这些反应的动力学。这些研究的结果可以直接用于模拟氧化老化过程中大气OA变化的模型。更广泛的影响：这项研究的结果将为气溶胶-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公立学校实施新的教育计划，参与实验室研究的本科生和研究生的培训，促进学生在各个层次上的科学发展。罗克斯伯里（波士顿一个经济落后的社区）的一所K-8学校将开发并实施一项针对6 -8年级学生的“天气与污染”推广计划。这将建立在一个现有的成功的中学生外展项目的基础上，在这个项目中，首席研究员（PI）小组的成员开发并运行了学校的第一个科学博览会项目，以及一个课后科学俱乐部。该项目最初将作为一所学校的试点项目实施，目标是通过教师培训扩展到波士顿公立学校系统的其他学校。这项工作也将促进本科和研究生水平的教育。本科生将通过麻省理工学院的本科生研究机会计划（针对麻省理工学院的学生）和麻省理工学院的暑期研究计划（针对来自其他学院传统上代表性不足的群体的学生）直接参与研究，其中PI是导师。拟议的研究将占研究生博士培训的很大一部分，研究生也将通过在拓展项目中发挥主要作用并为本科生提供建议而获得教育经验。研究结果将被纳入PI的本科和研究生水平的课堂教学。

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.