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), HCFC142b (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 (HFC134a), 18.4 (HFC-125), 17.7 (HFC-143a) and 10.5 (HFC32). 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 sigma 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 HFC32 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.