AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
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TD-DFT Investigation of the UV-Vis Spectra of Organonitrogen Chromophores in Brown Carbon
JIN CHEN, Emmy Rodriguez, Huanhuan Jiang, Alexander Frie, Haofei Zhang, Roya Bahreini, Ying-Hsuan Lin, University of California, Riverside
Abstract Number: 577 Working Group: Biomass Combustion: Emissions, Chemistry, Air Quality, Climate, and Human Health
Abstract Aerosol’s radiative forcing is one of the most uncertain drivers of climate cooling and warming. Brown carbon (BrC), light-absorbing organic compounds in aerosols, are estimated to account for ~20% of the tropospheric heating. Recent studies have identified nitroaromatics, conjugated systems, and Maillard reaction products as major BrC chromophores. However, light-absorbing properties of these BrC chromophores from various emission sources (e.g., biomass burning) and precursors have not been fully characterized. This is in part due to incomplete knowledge of their molecular structures and lack of authentic standards. In this study, we investigated the light absorption spectra of organonitrogen compounds as potential BrC chromophores by utilizing computational chemistry approaches. The time-dependent density functional theory (TD-DFT) combined with pure or hybrid functionals (e.g., PBE or B3LYP) was used to compute the excited state molecular geometry and light absorption spectra of tested organonitrogen compounds. In addition, basis sets such as 6-311++G** was incorporated to include diffusion and polarization functions. To explore the solvent effects on the light absorption, the UV-Vis spectra of tested compounds were predicted in gas phase and methanol environment. Calculated UV-Vis spectra were compared with experimental data measured from authentic standards to evaluate the accuracy of our computational predictions accounting for functionals, basis sets and solvent effects. Results from this study will have important implications in identification of potential BrC chromophores and their light absorption properties.