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

Abstract

Abstract. High frequency measurements of trifluoromethane (HFC-23, CHF 3 ), a potent hydrofluorocarbon greenhouse gas, largely emitted to the atmosphere as a by-product of the production of the hydrochlorofluorocarbon HCFC-22 (CHClF 2 ), 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 −1 at the end of 2016, representing a 28 % increase from 22.6 ± 0.4 pmol mol −1 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 −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 pmol mol −1 yr −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 ± 0.6 Gg yr −1 and then declined to 12.7 ± 0.6 Gg yr −1 (157 Mt CO 2 eq. yr −1 ) 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 2 eq.), which led to an increase in radiative forcing of 1.0 ± 0.1 mW m −2 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 % ofPublished by Copernicus Publications on behalf of the European Geosciences Union. 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.

Atmospheric histories, growth rates and solubilities in seawater and other natural waters of the potential transient tracers HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, HFC-125, HFC-23, PFC-14 and PFC-116

“…In 1973, Lovelock et al (1973) first proposed that CFC-12 can be used as a transient tracer to study water masses in the ocean. Subsequently, large numbers of studies (Gammon et al, 1982;Weiss et al, 1985;Smethie et al, 1988;Körtzinger et al, 1999;Tanhua et al, 2008;Smith et al, 2016;Fine et al, 2017) using CFC-12 as an oceanic transient tracer have been published. In the 1990s, the World Ocean Circulation Experiments (WOCE) used CFC-12 as the normal tracer to investigate global ocean circulation and mixing.…”

Perfluorocyclobutane (PFC-318, <i>c</i>-C<sub>4</sub>F<sub>8</sub>) in the global atmosphere

“…and HFC-23 emissions may also co-occur as HCFC-22 is produced from CHCl 3 and HFC-23 is a by-product that in developing countries is probably again vented to the atmosphere since the UNFCCC Clean Development Mechanism (CDM) funding to avoid HFC-23 emissions has expired (Simmonds et al, 2018;Say et al, 2019). While the global atmospheric lifetime of TFE is only ~2 days, the lifetime of HFP is ~6 days (Acerboni et al, 2001), so that HFP may be detectable near strong emission sources and serve as a sensitive marker for regional TFE/HFP/PTFE/FEP production.…”

Lagrangian simulations of the transport of young air masses to the top of the Asian monsoon anticyclone and into the tropical pipe

“…Radiatively active species transported into the lowermost extratropical stratosphere have a significant impact on surface climate (e.g. Solomon et al, 2010;Riese et al, 2012;Hossaini et al, 2015) or can cause regional radiative forcing like that caused by the Asian tropopause aerosol layer (ATAL) (e.g. Vernier et al, 2015).…”