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Changing trends and emissions of hydrochlorofluorocarbons (HCFCs) and their hydrofluorocarbon (HFCs) replacements
oleh: P. G. Simmonds, M. Rigby, A. McCulloch, S. O'Doherty, D. Young, J. Mühle, P. B. Krummel, P. Steele, P. J. Fraser, A. J. Manning, R. F. Weiss, P. K. Salameh, C. M. Harth, R. H. J. Wang, R. G. Prinn
Format: | Article |
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Diterbitkan: | Copernicus Publications 2017-04-01 |
Deskripsi
High-frequency, in situ global observations of HCFC-22 (CHClF<sub>2</sub>), HCFC-141b (CH<sub>3</sub>CCl<sub>2</sub>F), HCFC-142b (CH<sub>3</sub>CClF<sub>2</sub>) and HCFC-124 (CHClFCF<sub>3</sub>) and their main HFC replacements, HFC-134a (CH<sub>2</sub>FCF<sub>3</sub>), HFC-125 (CHF<sub>2</sub>CF<sub>3</sub>), HFC-143a (CH<sub>3</sub>CF<sub>3</sub>) and HFC-32 (CH<sub>2</sub>F<sub>2</sub>), 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<sup>−1</sup>, respectively, in 2015. HCFC-124 reached a maximum global mean mole fraction of 1.48 pmol mol<sup>−1</sup> in 2007 and has since declined by 23 % to 1.14 pmol mol<sup>−1</sup> in 2015. The HFCs all show increasing global mean mole fractions. In 2015 the global mean mole fractions (pmol mol<sup>−1</sup>) 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<sup>−1</sup>, in CO<sub>2</sub> equivalent units (CO<sub>2</sub> eq.) 0.76 ± 0.1 Gt yr<sup>−1</sup>, compared with 483 ± 70 Gg yr<sup>−1</sup> (0.82 ± 0.1 Gt yr<sup>−1</sup> CO<sub>2</sub> 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<sup>−1</sup> (0.65 ± 0.12 Gt yr<sup>−1</sup> CO<sub>2</sub> eq.) in 2015 compared to 240 ± 50 Gg yr<sup>−1</sup> (0.47 ± 0.08 Gt yr<sup>−1</sup> CO<sub>2</sub> 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.