Investigating Fundamental Chemical and Physical Processes Affecting Gas-Particle Partitioning Using Levitated Droplet-Mass Spectrometry

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This award is supported by the Environmental Chemical Sciences Program of the Division of Chemistry. Professor Frank Keutsch of Harvard University and his students investigate the fundamental processes involved in separating compounds between the air and the surface of particles (aerosols) in the atmosphere. This portioning between the air and the surfaces of solids that are present in the air is poorly understood however, one phase may be preferred over the other due to incomplete mixing, physical barriers, and/or chemical reactions on the aerosol particles. Laboratory studies are conducted on single aerosol particles to isolate and investigate how and why compounds stick to their surfaces. These experimental studies provide fundamental parameters for improving computer models on aerosol formation and changes in these particles with time (ageing). This research is important as it may ultimately improve regional and global models of aerosols, which are relevant to air quality and human and animal health. Professor Keutsch also designs laboratory experiments to introduce a systems approach to undergraduate education. This approach considers not only individual reactions but the coupled chemical and physical feedbacks that exist between different parts of the whole system (in this case, the gas and solid phases). His students learn about instrumentation design and reactions at and far from equilibrium. In addition, underrepresented high school students at Cambridge, MA high schools are mentored and work in the research laboratory learning to communicate their research to others in the field and gaining confidence in their abilities to participate in scientific fields. A new approach is used to study aerosol partitioning that combines levitation of individual micron-sized particles with mass-spectrometric (MS) detection. This technique allows the measurement of the molecular-level evolution of a droplet over atmospherically relevant time scales. Molecular-level detection is a novel approach that may advances trapped droplet methods. After further optimization of the trapped-droplet MS, specific research questions related to the role of non-ideal mixing, oligomer formation, transition metal complex photochemistry, and aerosol physical properties in gas-particle partitioning are addressed. This research is done in collaboration with chemists and atmospheric sciences. Results are compared with state-of-the-art models which improve the representation of the fundamental chemical and physical processes in the models, and hence, improve predictive capabilities.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.