Atmospheric OH Oxidation Chemistry of Particulate Liquid Crystal Monomers: An Emerging Persistent Organic Pollutant in Air

Liquid crystal monomers (LCMs) are synthetic chemicals widely used in liquid crystal displays such as televisions and smartphones and have recently been detected in indoor dust. Despite extensive use, the atmospheric fate of LCMs is unknown. Here, the heterogeneous OH oxidation of LCMs was studied by exploring the kinetics and mechanisms of 1-ethyl-4-(4-(4-propylcyclohexyl)phenyl)benzene (EPPB) and 4′′-ethyl-2′-fluoro-4-propyl-1,1′:4′,1′′-terphenyl (EFPT) coated onto ammonium sulfate particles. The measured heterogeneous rate constants for EPPB and EFPT were (7.05 ± 0.46) × 10 –13 and (4.67 ± 0.25) × 10 –13 cm 3 molecule –1 s –1,respectively, equivalent to atmospheric lifetimes of up to 25 and 38 days. These lifetimes are significantly longer than previously predicted values (<1 day) for these LCMs, indicating that they are much more persistent in air than predicted, with the potential to undergo long-range transport. Furthermore, 66 transformation products from the heterogeneous photooxidation of these LCMs were identified for the first time. Given the known toxicity of the parent LCMs, their measured persistence in the atmosphere, and the demonstrated complexity of their products, the present results not only underscore the need to quantify the levels of LCMs in ambient air, but also suggest that the presence of their transformation products should not be ignored when assessing the risks of airborne LCMs.