Chromophoric organic matter referred to as brown carbon (BrC) directly impacts radiative forcing in the atmosphere and drives aerosol photochemistry through radical formation and excited state-sensitization reactions. Secondary formation of BrC in atmospheric water and aqueous secondary organic aerosols (aqSOA) has been indicated as an important source of BrC, however, the chemical formation and photochemical aging is poorly understood. In aqueous aerosols or cloud droplets, reactions of dicarbonyls involving ammonium (NH<sub>4</sub><sup>+</sup> ) ions can form nitrogen-containing aromatics such as imidazole and pyrazine compounds. Many of the products formed from these secondary reactions have absorption extending into the near UV and visible parts of the solar spectrum making their photochemical properties of fundamental importance in understanding the role of aqueous BrC in the atmosphere. The presented research will characterize the molecular identity and spectroscopic properties of synthetic BrC compounds derived from glyoxal and pyruvic acid reactions with ammonium sulfate. The synthesized BrC samples were irradiated with a solar simulator to analyze changes in their spectroscopic properties and determine their atmospheric half-lives with respect to direct photolysis and OH oxidation.

Photochemical properties of aqueous brown carbon derived from dicarbonyls and ammonium

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