A time-dependent density functional theory investigation of the atmospheric absorption spectra of polycyclic aromatic hydrocarbons (PAHs) and their derivatives (Alkyl-PAHs, oxygenated-PAHs, and Nitrated-PAHs) over an urban area in China

• Published in: Journal of environmental chemical engineering 2022-12, Vol.10 (6), p.108853, Article 108853
• Main Authors: González-Berdullas, Patricia, Cruz, Cristiano N.M., Bandowe, Benjamin A.Musa, Esteves da Silva, Joaquim C.G., Pinto da Silva, Luís
• Format: Article
• Language: English
• Subjects: Absorption spectra; Brown carbon; Density functional theory; Organic aerosols; Polycyclic aromatic hydrocarbons; Radiative forcing
• ISSN: 2213-3437; 2213-3437
• DOI: 10.1016/j.jece.2022.108853

Polycyclic aromatic hydrocarbons (PAHs) and their oxygenated (OPAHs) and nitrated (NPAHs) derivatives are main chromophores of the carbonaceous aerosol brown carbon (BrC), which is linked with radiative forcing. Here, we investigated the atmospheric absorption spectra of 64 PAHs, OPAHs, and NPAHs directly over the Chinese megacity of Xi’an, by employing a time-dependent density functional theory (TD-DFT) computational approach and correcting the results for the experimentally determined atmospheric concentration of the studied molecules. The obtained data showed that these molecules contribute more to radiative forcing by absorbing light in the UVA and (sub)visible region of the spectrum. Investigating “daily” absorption spectra revealed major seasonal variation in the intensity of light absorption, but little changes in the shape of the absorption spectra. The observed light absorption can be explained mainly by contributions from PAHs and to a lesser extent by carbonyl-OPAHs, with relatively low contributions of the other OPAHs and NPAHs. Among them, benzo[b+j+k]fluoranthenes, benzo[e]pyrene, benzo[a]pyrene, benzo[ghi]perylene, indeno[1,2,3-cd]pyrene, 6H-benzo[cd]pyren-6-one, 7H-benz[de]anthracen-7-one, and benz[a]anthracene-7,12-dione are highlighted as potentially problematic contributors for radiative forcing over Xi’an. [Display omitted] •The atmospheric absorption spectra of 64 PACs over Xi’an (China) was obtained.•TD-DFT calculations and experimental data were combined to produce the spectra.•PAHs are the most important class of light-absorbing molecules.•Light-absorption is more problematic in the UVA and (sub)visible range.•Light-absorption intensities are significantly affected by seasonal variation.