Modeling the nocturnal/diurnal and seasonal real world absorption spectra of polycyclic aromatic hydrocarbons and their derivatives in two Chinese polluted cities

Abstract

Brown carbon (BrC), an organic aerosol, plays an important role in radiative forcing. Polycyclic aromatic hydrocarbons (PAHs) and their derivatives such as oxygenated and nitrated polycyclic aromatic hydrocarbons (OPAHs & NPAHs) are the major constituents of BrC and are persistent environmental pollutants. Our strategy here is to utilize time dependent-density functional theory (TD-DFT) to model the absorption spectra of PAHs and their derivatives in two Chinese industrial sites: Qingcheng district (site A) and Longtang town of Qingyuan (site B). These data are corrected for “Real-world” experimental concentrations of PAHs over these cities. For the first time, nocturnal/diurnal and seasonal variations of PAHs are being simultaneously studied under a theoretical framework. These findings show that the absorptions at site A and B take place mainly due to PAHs while OPAHs and NPAHs have negligible contribution. The site A is highly affected by climate forcing caused by these PAHs. The absorption in winter is higher as compared to that of in summer. Our theoretical modeling approach remarkably identifies the most relevant PAHs for climate forcing in both Chinese regions.