Recent increases in the atmospheric growth rate and emissions of HFC-23 (CHF₃) and the link to HCFC-22 (CHClF₂) production

摘要: High frequency measurements of trifluoromethane (HFC-23, CHF₃), a potent hydrofluorocarbon greenhouse gas, largely emitted to the atmosphere as a by-product of the production of the hydrochlorofluorocarbon HCFC-22 (CHClF₂), at five core stations of the Advanced Global Atmospheric Gases Experiment (AGAGE) network, combined with measurements on firn air, old Northern Hemisphere air samples and Cape Grim Air Archive (CGAA) air samples, are used to explore the current and historic changes in the atmospheric abundance of HFC-23. These measurements are used in combination with the AGAGE 2-D atmospheric 12-box model and a Bayesian inversion methodology to determine model atmospheric mole fractions and the history of global HFC-23 emissions. The global modelled annual mole fraction of HFC-23 in the background atmosphere was 28.9 ± 0.6 pmolmol⁻¹ at the end of 2016, representing a 28% increase from 22.6 ± 0.4 pmolmol⁻¹ in 2009. Over the same time frame, the modelled mole fraction of HCFC-22 increased by 19% from 199 ± 2 to 237 ± 2 pmolmol⁻¹. However, unlike HFC-23, the annual average HCFC-22 growth rate slowed from 2009 to 2016 at an annual average rate of -0.5 pmolmol⁻¹yr⁻². This slowing atmospheric growth is consistent with HCFC-22 moving from dispersive (high fractional emissions) to feedstock (low fractional emissions) uses, with HFC-23 emissions remaining as a consequence of incomplete mitigation from all HCFC-22 production. Our results demonstrate that, following a minimum in HFC-23 global emissions in 2009 of 9.6±0.6, emissions increased to a maximum in 2014 of 14.5±0 …