Understanding the Burst of Hydroxyl Radicals (OH) in Newly Formed Cloud Droplets

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Aerosol particles and aerosol-cloud interactions remain one of the least constrained aspects in global climate modeling and prediction efforts. To help increase current understanding, the PI seeks to characterize reaction mechanisms in aerosol particles that have shown recently to produce light-induced initial bursts of the most oxidizing species, hydroxyl radical (OH). Focus will be on trace metals and organic peroxides, latter of which represent a new class of molecules to be studied in this context. Results from ambient aerosol analyses, laboratory simulations and chamber experiments will inform parametrization of OH production for incorporation into larger scale climate models. The project aims at increasing understanding of mechanisms of atmospheric production of OH in cloud droplets. The work is motivated by the PI’s observation of an initial and substantial burst in OH production when exposing aerosols to near-UV radiation. Identifying new OH sources in cloud droplets has important and potentially transformative implications on many chemical and physical atmospheric processes that affect global climate and human health. The three-pronged experimental approach consists of measuring OH production in (i) collected and chemically analyzed ambient aerosols of various types; (ii) controlled laboratory experiments using a series of synthesized (hydro)peroxides, trace metals, and varying pH, conductivity, and wavelength; and (iii) chamber generated aerosol particles. A new semi-portable instrument (direct-to liquid OH analyzer) is sought to be developed that allows aerosols to grow to droplets that are collected and analyzed for OH formation on the time scale of tens of minutes to hours. Chemical kinetic modeling of results from all components of the experimental approach will be used to derive rate constants and parametrization for implementation in larger scale models. Two graduate students will receive training through this project, and a number of undergraduate students from underrepresented populations will be recruited from existing programs on the PI’s campus.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.