Recent increases in the atmospheric growth rate and emissions of HFC-23 (CHF<sub>3</sub>) and the link to HCFC-22 (CHClF<sub>2</sub>) production
High frequency measurements of trifluoromethane (HFC-23, CHF<sub>3</sub>), a potent hydrofluorocarbon greenhouse gas, largely emitted to the atmosphere as a by-product of the production of the hydrochlorofluorocarbon HCFC-22 (CHClF<sub>2</sub>), at five core stations of th...
| Principais autores: | , , , , , , , , , , , , , , , , , , , , , |
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| Formato: | Artigo |
| Idioma: | English |
| Publicado em: |
Copernicus Publications
2018-03-01
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| coleção: | Atmospheric Chemistry and Physics |
| Acesso em linha: | https://www.atmos-chem-phys.net/18/4153/2018/acp-18-4153-2018.pdf |
| Resumo: | High frequency measurements of trifluoromethane (HFC-23, CHF<sub>3</sub>), a potent
hydrofluorocarbon greenhouse gas, largely emitted to the atmosphere as a
by-product of the production of the hydrochlorofluorocarbon HCFC-22
(CHClF<sub>2</sub>), 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 pmol mol<sup>−1</sup> at the end of
2016, representing a 28 % increase from 22.6 ± 0.4 pmol mol<sup>−1</sup> in
2009. Over the same time frame, the modelled mole fraction of HCFC-22
increased by 19 % from 199 ± 2 to 237 ± 2 pmol mol<sup>−1</sup>. However, unlike HFC-23, the annual average HCFC-22 growth rate
slowed from 2009 to 2016 at an annual average rate of −0.5 pmol mol<sup>−1</sup> yr<sup>−2</sup>. 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.<br><br>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 ± 0.6 Gg yr<sup>−1</sup> and then declined to 12.7 ± 0.6 Gg yr<sup>−1</sup>
(157 Mt CO<sub>2</sub> eq. yr<sup>−1</sup>) in 2016. The 2009
emissions minimum is consistent with estimates based on national reports and
is likely a response to the implementation of the Clean Development
Mechanism (CDM) to mitigate HFC-23 emissions by incineration in developing
(non-Annex 1) countries under the Kyoto Protocol. Our derived cumulative
emissions of HFC-23 during 2010–2016 were 89 ± 2 Gg
(1.1 ± 0.2 Gt CO<sub>2</sub> eq.), which led to an increase in radiative forcing of 1.0 ± 0.1 mW m<sup>−2</sup> over the same period. Although the CDM had reduced global
HFC-23 emissions, it cannot now offset the higher emissions from increasing
HCFC-22 production in non-Annex 1 countries, as the CDM was closed to new
entrants in 2009. We also find that the cumulative European HFC-23 emissions
from 2010 to 2016 were ∼ 1.3 Gg, corresponding to just 1.5 %
of cumulative global HFC-23 emissions over this same period. The majority of
the increase in global HFC-23 emissions since 2010 is attributed to a delay
in the adoption of mitigation technologies, predominantly in China and East
Asia. However, a reduction in emissions is anticipated, when the Kigali 2016
amendment to the Montreal Protocol, requiring HCFC and HFC production
facilities to introduce destruction of HFC-23, is fully implemented. |
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| ISSN: | 1680-7316 1680-7324 |