Atmospheric fate of typical liquid crystal monomers in the tropospheric gas, liquid, and granular phases

Abstract

Mineral aerosol particles significantly impact environmental risk prediction of liquid crystal monomers (LCMs). In this work, we investigated the reaction mechanisms and kinetics of three typical LCMs (4-cyano-3,5-difluorophenyl 4-ethylbenzoate (CEB-2F), 4-cyano-3-fluorophenyl 4-ethylbenzoate (CEB-F), and 4-cyanophenyl 4-ethylbenzoate (CEB)) with ozone (O3) in the atmospheric gas, liquid, and particle phases employing density functional theory (DFT). Here, O3 is prone to add to the benzene ring without F atom(s) in the selected LCMs. The ozonolysis products are aldehydes, carboxylic acids, epoxides, and unsaturated hydrocarbons containing aromatic rings. Those products undergo secondary ozonolysis to generate small molecular compounds such as glyoxal, which is beneficial for generating secondary organic aerosol (SOA). Titanium dioxide (TiO2), an essential component of mineral aerosol particles, has good adsorption properties for LCMs; however, it slightly reduces the reactivity with O3. At 298 K, the reaction rate constant of the selected LCMs reacting with O3 in the gas and atmospheric liquid phases is (2.74‒5.53) × 10−24 cm3/(mol·sec) and 5.58 × 10−3‒39.1 L/(mol·sec), while CEB-2F reacting with O3 on (TiO2)6 cluster is 1.84 × 10−24 cm3/(mol·sec). The existence of TiO2 clusters increases the persistence and long-distance transportability of LCMs, which enlarges the contaminated area of LCMs.