Updated global warming potentials of inhaled halogenated anesthetics, isoflurane and sevoflurane from new temperature dependent OH-kinetics

Despite the use of scavenging systems in anesthesia machines, inhaled halogenated anesthetic gases (HAGs), such as isoflurane (CF₃CHClOCHF₂) and sevoflurane ((CF₃)₂CHOCH₂F), are still emitted directly into the atmosphere. In 2014, their atmospheric concentrations were 0.097 ppt (isoflurane) and 0.13 pptv (sevoflurane). As halogenated species, their impact on global warming has to be known. Notably, the global warming potential at a time horizon of 100 years (GWP_{100 years}) for sevoflurane differs between IPCC and WMO sources, creating regulatory uncertainty. For that reason, in this work GWP_{100 years} for isoflurane and sevoflurane was reevaluated from the atmospheric chemical lifetimes, <i>τ</i>OHHAG, derived from the kinetic study of the gas-phase reactions of hydroxyl (OH) radicals with the HAGs and the radiative efficiencies (REs) derived from the (IR) absorption cross sections in the atmospheric window (1500-500 cm^-1). The temperature dependence of the OH-rate coefficients (<i>k</i>₁(<i>T</i>) for isoflurane and <i>k</i>₂(<i>T</i>) for sevoflurane) between 263 and 353 K was determined at 100 Torr by using the pulsed laser photolysis/laser-induced fluorescence technique. The obtained Arrhenius expressions are <i>k</i>₁(<i>T</i>) = (1.1 ± 0.5) × 10^-13 exp{-(1234 ± 144)/<i>T</i>} and <i>k</i>₂(<i>T</i>) = (1.6 ± 0.7) × 10^-12 exp{-(1065 ± 138)/<i>T</i>} cm³ molecule^-1 s^-1. At 272 K, a <i>τ</i>OHHAG of 3.0 years for isoflurane and 1.2 years for sevoflurane were estimated relative to CH₃CCl₃ from <i>k</i>₁ and <i>k</i>₂. Moreover, the ultraviolet (UV) absorption cross sections were determined between 190 and 400 nm at 298 K, and the absorption was found to be negligible above 290 nm, indicating minimal photolysis by sunlight. In contrast, the IR absorption in the atmospheric window is significant and the IR absorption cross sections (4000-500 cm^-1) were determined by Fourier Transform infrared spectroscopy. The lifetime-corrected radiative efficiencies (REs) were 0.44 and 0.30 W m^-2 ppbv^-1 for isoflurane and sevoflurane, respectively. From lifetime-corrected REs and <i>τ</i>OHHAG, GWP_{100 years} was estimated to be 508 for isoflurane (5% lower than IPCC/WMO values) and 125 for sevoflurane (36% lower than IPCC and 11% lower than WMO). These findings confirm isoflurane to be a high-GWP gas (above 150) according to the EU 2024 regulation, while sevoflurane does not meet the high-GWP threshold. A reassessment of the IPCC and WMO values is recommended.