Theoretical study on the mechanisms, kinetics and risk assessment of OH radicals and Cl atom initiated transformation of HCFC-235fa in the atmosphere.

Hydrochlorofluorocarbons (HCFCs) are important greenhouse gases and ozone-depleting substances. Thus, a thorough understanding of their atmospheric fate is essential for preventing and controlling atmospheric pollution. Herein, the atmospheric transformation mechanism of CFCHCClF (HCFC-235fa) by the OH radical and the Cl atom was carried out at the dual-level of CCSD(T)/aug-cc-pVTZ//M06-2X/6-311+G(d,p). The reaction rate coefficients were calculated using the multistructural canonical variational transition state theory with small curvature tunneling (MS-CVT/SCT) at 200-1000 K. The (CFCHCClF + OH) and (CFCHCClF + Cl) values are 9.05 × 10 and 1.95 × 10 cm molecule s at 297 K, respectively. The results show that the role of OH is more important than Cl in the degradation of CFCHCClF. The atmospheric lifetimes (83 days-77.93 years), ozone destruction potential (0.001-0.023), and global warming potentials (GWP = 21.06-5157.35) of CFCHCClF were assessed, and these results indicate that CFCHCClF is atmospherically persistent and environmentally unfriendly. The evolution mechanisms of CFC·HCClF, CFC(OO˙)HCClF, and CFC(O˙)HCClF in the presence of O, HO˙, and NO were investigated and discussed. The resulting products of CFCHCClF are mostly highly oxidized multi-functional compounds in the forms of aldehydes, ketones, and organic nitrates. A computational assessment of acute and chronic toxicities was performed at three levels of nutrition in order to improve the understanding of the potential toxicity of CFCHCClF and its degradation products to the aquatic environment. The acidification potential of CFCHCClF was calculated to be 1.141 and presumed to contribute to the formation of acid rain. The results may contribute to describing HCFCs' atmospheric fate, persistence, and environmental risks.