Brown carbon (BrC) aerosols are made up of molecular chromophores which absorb in the visible to near-ultraviolet regions, dramatically influencing the aerosol optical properties. These aerosols play an important role in the solar energy exchange in Earth’s atmosphere, as well as having dramatic impacts on human health. Despite previous studies having characterized the main functional groups of BrC chromophores, there remain unanswered questions regarding the molecular-level absorption outcomes following exposure to solar radiation. To address this knowledge gap, we leveraged a suite of conformation-specific techniques such as resonant two-photon ionization (R2PI), ultraviolet hole-burning (UVHB), and resonant ion-depletion infrared spectroscopy (RIDIRS) to study the relationship between the chromophore structure and its photophysical characteristics with and without water microsolvation. In particular, we investigated the single-conformation spectroscopy of molecular complexes between 2-phenyl-1-H-pyrrole, 2-phenylimadazole and 4-phenylimidazole with water under jet-cooled conditions. These molecular beam studies were also complemented with UV-Vis and fluorescence studies to model the chromophore-water complex interactions within bulk-phase aerosol environments. Our results reveal a bottom-up perspective of BrC chromophore absorption properties by mimicking the local water solvation environments in atmospheric aerosols.

Exploring the photophysics of brown carbon chromophores using laser-based spectroscopy and computational methods

ACS Spring 2022

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