Formation and Evolution of Atmospheric Brown Carbon from Nitrate Radical Initiated Oxidation of Heterocyclic Volatile Organic Compounds

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Brown carbon (BrC) particles in biomass burning plumes affect climate through their interaction with radiation and Earth’s energy budget, yet, little is known about their formation and radiative characteristics. In this multi-PI project, atmospheric formation and transformation processes of BrC particles are studied in systematic laboratory experiments using sophisticated analytical tools. Resulting new mechanistic information will aid in the interpretation of field observations and inform predictive climate models. The project aims at increasing understanding of mechanisms of atmospheric oxidation of heterocyclic volatile organic carbons (VOCs) as sources of brown carbon (BrC) secondary organic aerosols (SOA). Systematic laboratory chamber and flow reactor experiments will be carried out that mimic nighttime conditions in which relevant VOCs are oxidized initially with nitrate radical (NO3) and subsequently aged diurnally with NO3 and hydroxyl (OH) radicals. A suite of on- and off-line state-of-the-art instruments will be employed to characterize particles’ physical and chemical properties, including size, optical parameters, molecular composition, and functional groups. In addition, a multiphase kinetic model will be developed with the data obtained from compositional measurements. The outcome of this work will aid in the interpretation of observations made in complex real biomass burning systems and provide fundamental mechanistic information that can be incorporated into larger scale climate models. Three graduate students will carry out the bulk of the laboratory work, and a number of undergraduate students from underrepresented populations will be recruited from existing programs on the PIs campus. Outreach activities include engagement with local high schools.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.