Changing trends and emissions of hydrochlorofluorocarbons (HCFCs) and their hydrofluorocarbon (HFCs) replacements

High-frequency, in situ global observations of HCFC-22 (CHClF₂), HCFC-141b (CH₃CCl₂F), HCFC-142b (CH₃CClF₂) and HCFC-124 (CHClFCF₃) and their main HFC replacements, HFC-134a (CH₂FCF₃), HFC-125 (CHF₂CF₃), HFC-143a (CH₃CF₃) and HFC-32 (CH₂F₂), have been used to determine their changing global growth rates and emissions in response to the Montreal Protocol and its recent amendments. Global mean mole fractions of HCFC-22, -141b, and -142b have increased throughout the observation period, reaching 234, 24.3 and 22.4 pmol mol⁻¹, respectively, in 2015. HCFC-124 reached a maximum global mean mole fraction of 1.48 pmol mol⁻¹ in 2007 and has since declined by 23 % to 1.14 pmol mol⁻¹ in 2015. The HFCs all show increasing global mean mole fractions. In 2015 the global mean mole fractions (pmol mol⁻¹) were 83.3 (HFC-134a), 18.4 (HFC-125), 17.7 (HFC-143a) and 10.5 (HFC-32).<br><br> The 2007 adjustment to the Montreal Protocol required the accelerated phase-out of emissive uses of HCFCs with global production and consumption capped in 2013 to mitigate their environmental impact as both ozone-depleting substances and important greenhouse gases. We find that this change has coincided with a stabilisation, or moderate reduction, in global emissions of the four HCFCs with aggregated global emissions in 2015 of 449 ± 75 Gg yr⁻¹, in CO₂ equivalent units (CO₂ eq.) 0.76 ± 0.1 Gt yr⁻¹, compared with 483 ± 70 Gg yr⁻¹ (0.82 ± 0.1 Gt yr⁻¹ CO₂ eq.) in 2010 (uncertainties are 1<i>σ</i> throughout this paper). About 79 % of the total HCFC atmospheric burden in 2015 is HCFC-22, where global emissions appear to have been relatively similar since 2011, in spite of the 2013 cap on emissive uses. We attribute this to a probable increase in production and consumption of HCFC-22 in Montreal Protocol Article 5 (developing) countries and the continuing release of HCFC-22 from the large banks which dominate HCFC global emissions. Conversely, the four HFCs all show increasing mole fraction growth rates with aggregated global HFC emissions of 327 ± 70 Gg yr⁻¹ (0.65 ± 0.12 Gt yr⁻¹ CO₂ eq.) in 2015 compared to 240 ± 50 Gg yr⁻¹ (0.47 ± 0.08 Gt yr⁻¹ CO₂ eq.) in 2010. We also note that emissions of HFC-125 and HFC-32 appear to have increased more rapidly averaged over the 5-year period 2011–2015, compared to 2006–2010. As noted by Lunt et al. (2015) this may reflect a change to refrigerant blends, such as R-410A, which contain HFC-32 and -125 as a 50 : 50 blend