Chromophoric organic compounds in the atmosphere, termed ‘brown carbon’ (BrC), impact both air quality and radiative forcing in the climate. Recent studies have shown that aqueous reactions of dicarbonyls such as glyoxal and methylglyoxal with amines leads to the formation of colored products indicating a role in the production of atmospheric BrC. These reactions generate a variety of products including nitrogen-containing organic chromophores and high molecular weight oligomers, however there are still many aspects of the chemical structure and properties that remain unknown.&lt;span style="font-size:10.8333px"&gt; &lt;/span&gt;Excitation-emission matrix (EEM) spectroscopy is a technique commonly used in characterizing chromophoric dissolved organic matter (CDOM) in terrestrial water samples. This method provides insight into the optical properties of these samples as well as a means of classifying spectral features and their molecular origin. Consequently, it is now beginning to see increased usage in studies of both laboratory and environmental BrC samples making the overlap of these two fields particularly important.  Towards this goal, experimental results investigating the photochemical properties of BrC generated from reactions of glyoxal and methylglyoxal with ammonium sulfate and methyl amine using EEM spectroscopy will be presented. These results show significant differences in properties across the actinic UV including mass absorption coefficients, photolysis rates, and fluorescence quantum yields for samples generated from either glyoxal or methylglyoxal. The presented results will also focus on comparison to previous work on CDOM with this type of spectroscopy. In addition, the chemical composition of these samples is also investigated using electrospray ionization mass spectrometry (ESI-MS).

Photochemical studies of atmospheric brown carbon using excitation-emission matrix spectroscopy

2019 Fall National Meeting

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