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.
