Singlet oxygen is produced from brown carbon-containing cooking organic aerosols (BrCOA) under indoor lighting†

Abstract

Light absorbing organic molecules known as brown carbon (BrC) can be emitted during processes such as cooking and combustion in indoor environments. We hypothesized that indoor BrC-containing cooking organic aerosols, or BrCOA, can act as sensitizers to generate the first excited state of molecular oxygen, singlet oxygen (), under indoor lighting conditions. Here, we used an impinger to collect aerosols from a range of cooking dishes, including pancakes, pan-fried Brussels sprouts and vegetable stir-fries, and irradiated these samples in a photoreactor with UVA and fluorescent lights and on a sunlit windowsill. Using furfuryl alcohol as a probe for , we determined steady-state concentrations of using liquid chromatography and calculated apparent quantum yields for each BrCOA sample. Our results show that under all indoor lighting conditions tested, BrCOA can indeed sensitize . Specifically, in solutions of BrCOA from pancakes, pan-fried Brussels sprouts, and vegetable stir-fries under UVA light, the concentrations were 2.56 ± 1.24 × 10⁻¹³ M, 2.24 ± 1.51 × 10⁻¹³ M, and 3.12 ± 0.86 × 10⁻¹³ M, respectively. These results suggest that production is not dish-dependent, but rather produced across a range of BrCOA samples. We then normalized the concentrations to the rate of absorbance to obtain apparent quantum yields up to 6.1%. Both the quality and the quantity of the chromophoric BrCOA were important for predicting the apparent quantum yield. Moreover, the indoor sunlit experiments led to the highest concentrations observed, with important implications on the formation of oxidants in sunlit kitchens. These results demonstrate the ability of BrCOA to produce in indoor environments, and thus for to be a competitive indoor oxidant.