Density Functional Theory Calculation of the Absorption Properties of Brown Carbon Chromophores Generated by Catechol Heterogeneous Ozonolysis

Abstract

The effect of light-absorbing atmospheric particles on climate change has been incorporated into climate models, but the absence of brown carbon (BrC) in these models has been leading to significant differences between model predictions and measured data on radiative forcing. Also, little is known regarding the relationship between optical properties and chemical compositions of BrC. Thus, we have characterized the absorption properties of catechol and known heterogeneous ozonolysis products, with a theoretical approach based on density functional theory (DFT). While catechol presents a weak absorption maximum in the ultraviolet C (UVC) region, other polyaromatic derivatives present an absorption up to 6 times higher, with biphenyl-2,2′,3,3′-tetraol, biphenyl-3,3′,4,4′,5,5′-hexaol, and terphenyl-2′,3,3′,3″,4,4″-hexaol presenting the strongest absorption. Moreover, these derivatives now absorb in the ultraviolet B (UVB) and ultraviolet A (UVA) regions, which are types of actinic radiation in the ultraviole...