Multiphase Chemistry of Urea: Implications for Brown Carbon and Aerosol Mass

Anthropogenic activities have dramatically altered the nitrogen cycle affecting air quality, climate, and ecosystem health. Urea, a form of reactive nitrogen, has previously been detected in aerosols, precipitation, and most recently it has been reported in the gas-phase. Although measurements of urea are scarce, there is emerging evidence that suggests urea could be an unrecognized albeit important contributor to reactive nitrogen. This research investigates the atmospheric chemistry of urea focusing on how multiphase reactions could contribute to aerosol mass and alter optical properties of aerosols. Influenced by the industrial product of urea and glyoxal resins, we investigate the reaction of urea and glyoxal in bulk solutions that mimicked aerosol-like conditions. Experiments were carried out in order to understand if the urea-glyoxal reaction occurs and investigate how evaporation could be involved in this reaction. The reaction's absorption spectra were analyzed in the ultraviolet-visible wavelength region. The measurements indicate the formation of light absorbing organic aerosol. Overall, our findings suggest that reactions of urea with glyoxal in aqueous aerosol particles is a feasible pathway for creating light absorbing organic aerosols and could contribute to aerosol mass.