Stratospheric Ozone – HCFOs, CF3I and HFCs

HCFOs, CF3I Stratospheric Ozone and Climate Change

The HCFOs, HBFOs, CF3I (iodotrifluoromethane) that have been selected for a range of applications breakdown rapidly in the atmosphere and have ultra-low GWPs, whilst maintaining a good balance of technical and safety properties.

The HCFOs and HBFOs are HCFO-1224yd(Z), HCFO-1233zd(E) and HBFO-1233xfB. All are oxidised rapidly in the lower atmosphere with atmospheric lifetimes of 21 days [1], 26 days [2] and 7 days [3], respectively, CF3I has a lifetime of about 6 days [9]; hence all are very short lived substance (VSLS) [4] that, in view of their minimal effect on stratospheric ozone, are not listed as Ozone Depleting Substances in the Montreal Protocol.

The Montreal Protocol has a defined process for assessing new substances that the Scientific Assessment Panel has estimated to have a significant ozone-depleting potential (See Montreal Protocol Decisions on new substances, including Decision IX/24). HCFO-1233zd(E) has been reviewed and assessed by the Scientific Assessment Panel (see SAP2018).  The HCFOs do not have significant ozone depletion potentials.

It takes several months for a substance released in northern temperate regions of the world to be transported through the lower atmosphere before it is injected into the stratosphere. Consequently, very little of these halopropenes can be transported to the ozone layer. In the case of HCFO-1233zd(E), for material emitted between 30° and 60°N, an average Ozone Depletion Potential (ODP) has been calculated to be 0.00034 [5] and, on the same basis, that of HBFO-1233xfB is 0.0028 [6]. The ODP of HCFO-1224yd(Z) is reported as 0.00012 [1].  A more recent paper reported essentially the same ODP of HCFO-1233zd(E) at 0.0003 [7]. Due to their very short atmospheric lifetimes, these substances do not accumulate in the atmosphere and the global warming potentials (GWPs) of all substances are 1 or less than 1 [1,5,6]  (that is less than carbon dioxide at the 100 year time horizon).

Analyses [9] of potential effects of ozone for VSLSs such as CF3I showed very small effects on the total ozone column and almost all ozone loss occurring in the lower troposphere, where these VSLSs would essentially reduce the overall human‐produced ozone pollution and the paper concluded that the stratospheric ozone column ozone decrease due to CF3I emissions was essentially zero (within statistical error), while producing significant changes in tropospheric ozone. It photolyses rapidly to form reactive iodine atoms under a sunlit atmosphere and its lifetime and fate of decomposition products depends largely on location of the emissions.

The EU Ozone Regulation 1005/2009 defines controlled substances as ’ substances listed in Annex I, including their isomers, whether alone or in a mixture, and whether they are virgin, recovered, recycled or reclaimed;” The Guidance to Regulation (EC) No 1272/2008 on classification, labelling and packaging (CLP) of substances and mixtures  Version 5.0 – July 2017 in section 5.1 Hazardous to the Ozone Layer states that  “Any substances having an Ozone Depleting Potential (ODP) greater or equal to the lowest ODP (i.e. 0.005) of the substances currently listed in Annex I to Regulation (EC) No 1005/2009 should be classified as hazardous to the ozone layer (category 1).” The HCFOs have extremely low ODPs that are well below the threshold in the CLP guidance.

Designation Name and formula

GWP

 

Atmospheric lifetime

(days)

Ozone Depleting Potential Main Applications
HCFO-1224yd(Z)

2,3,3,3 Tetrafluoro-1-chloroprop-1-ene

 

CF3-CF=CHCl

< 1 [1] 21 [1] 0.00012 [1]

·              Refrigerant for centrifugal chillers, high temperature heat pumps

·              working fluid for organic rankine cycle (ORC)

·              Blowing agent for polyurethane foams

HBFO-1233xfB

 2-bromo-3,3,3-trifluoropropene

 

CF3CBr=CH2

0.26 [6] 7 [6] 0.0028 [6] ·              Fire extinguishant streaming agent (also known as 2-BTP)
HCFO-1233zd(E) Trans 1-Chloro-3,3,3-
trifluoroprop-1-eneTrans-CHCl=CHCF3
1 [8] 26 [2] 0.00034 [5]

·              Refrigerant for chiller applications, high temperature heat pumps

·              Working fluid for organic rankine cycle (ORC)

·              Blowing agent for Insulation foams

·              Precision solvents

The Ozone Depletion Potential Definition and Very Short- Lived Substances (CF3I and HCFOs)

The ozone depletion potential (ODP) concept was initially developed to measure the potential impact of long‐lived gases, those with multi-year atmosphere lifetimes, on stratospheric ozone.  For very short-lived substances (VSLSs) with atmospheric lifetimes less than a few months, such as the HCFOs and CF3I (iodotrifluoromethane), most of their effect occur in the troposphere. A recent paper [9] reconsiders the concept of ozone depletion potentials (ODPs) for such short‐lived chemicals to properly account for their impact on stratospheric and tropospheric ozone, noting that it is important to recognize that tropospheric ozone has increased substantially over the last century, largely as the result of emissions from human activities.

The ODP concept uses the decline in total ozone column (troposphere and stratosphere) because it is the total column decrease that is of concern to protecting humans and the biosphere from increases in ultraviolet radiation. Analyses of potential effects of ozone for VSLSs such as CF3I showed very small effects on the total ozone column and almost all ozone loss occurring in the lower troposphere, where these VSLSs would essentially reduce the overall human‐produced ozone pollution. The paper concludes that the stratospheric ozone column ozone decrease due to CF3I emissions was essentially zero (within statistical error), while producing significant changes in tropospheric ozone.

The paper suggests that policy considerations for VSLSs not only consider the traditional total column values for ODP but should also account for the ODP due to stratospheric ozone loss only, termed Stratospheric ODP (SODP), to help the ODP concept satisfy its primary requirement of protecting stratospheric ozone. For long‐lived species, ODP and SODP values should be nearly the same because almost all the ozone depletion occurs in the stratosphere. However, for many VSLSs, especially those with very short atmospheric lifetimes, ODP and SODP values can be quite different.

To further investigate the SODP concept, the paper examined the most recent published literature for ODPs determined for other VSLSs, including HCFO-1233zd(E). For this HCFO the paper concluded that most of the total ozone column decrease occurred in the troposphere (~ 53%), reducing the already extremely small potential effect on stratospheric ozone even further.

References

  1. Measured by the National Institute of Advanced Industrial Science and Technology, Japan (AIST); GWP calculated according to the IPCC AR5 method.
  2. Myhre, G., D. Shindell, F.-M. Bréon, W. Collins, J. Fuglestvedt, J. Huang, D. Koch, J.-F. Lamarque, D. Lee, B. Mendoza, T. Nakajima, A. Robock, G. Stephens, T. Takemura and H. Zhang, 2013: Anthropogenic and Natural Radiative Forcing. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
  3. Patten, K. O., V. G. Khamaganov, V. L. Orkin, S. L. Baughcum, and D. J. Wuebbles (2011), OH reaction rate constant, IR absorption spectrum, ozone depletion potentials and global warming potentials of 2-bromo-3,3,3-trifluoropropene, J. Geophys. Res., 116, D24307, doi:10.1029/2011JD016518.
  4. Ko M.K.W. and 32 others, Very Short-Lived Halogen and Sulphur Substances, Chapter 2 of Scientific Assessment of Ozone Depletion: 2002, Global Ozone Research and Monitoring Project – Report No. 47, World Meteorological Organization, Geneva, 2002.
  5. Patten, K. O. and Wuebbles, D. J.: Atmospheric lifetimes and Ozone Depletion Potentials of trans-1-chloro-3,3,3-trifluoropropylene and trans-1,2-dichloroethylene in a three-dimensional model, Atmos. Chem. Phys., 10, 10867-10874, https://doi.org/10.5194/acp-10-10867-2010, 2010.
  6. Patten, K. O., V. G. Khamaganov, V. L. Orkin, S. L. Baughcum, and D. J. Wuebbles (2012), Correction to “OH reaction rate constant, IR absorption spectrum, ozone depletion potentials and global warming potentials of 2-bromo-3,3,3-trifluoropropene,” J. Geophys. Res., 117, D22301, doi:10.1029/2012JD019051.
  7. Sulback Andersen, M.P., J.A. Schmidt, A. Volkova, and D.J. Wuebbles, A three-dimensional model of the atmospheric chemistry of E and Z-CF3CH=CHCl (HCFO-1233(zd) (E/Z)), Environ., 179, 250−259, doi:10.1016/j.atmosenv.2018.02.018, 2018.
  8. IPCC Working Group I – The Physical Science Basis– Chap.8 Annex 8.A.1, 5th Assessment Report
  9. Revising the Ozone Depletion Potentials Metric for Short‐Lived Chemicals Such as CF3I and CH3I, Jun Zhang, Donald J. Wuebbles, Douglas E. Kinnison, and Alfonso Saiz‐Lopez, JGR Atmospheres, Volume 125, Issue9 , 16 May 2020, https://doi.org/10.1029/2020JD032414

HFCs have negligible effect on the ozone layer

Over 20 years ago it was established that HFCs have no chemical effect on stratospheric ozone [1].

However, it has been postulated that a potential effect of HFCs on stratospheric temperatures may augment the reactions that deplete stratospheric ozone [2]. The calculations were performed by computer modelling using scenarios of future HFC production and release up to the year 2050.

The scenarios initially used were those of Velders et al. (2009) [3] which have very large HFC releases up to 2050. These scenarios did not have any constraints on HFC releases, so that not even the original F-gas Regulation and Directive of the EU were considered [4, 5]. The scenarios have been effectively discredited and superseded by more realistic scenarios. These incorporate the revised EU F-gas regulation [6], together with the proposed North American phase-down of HFC use and will result in reduced future emissions of HFCs to the point where they are similar to those envisaged in the scenarios used by climate scientists for the IPCC’s 5th Assessment Report [7].

Under the IPCC scenarios accumulation of HFCs in the atmosphere should be reduced by at least 90% from the large emissions assumed by Hurwitz et al (2015) [2]. The change in stratospheric temperature (about 0.02°K) would then be insignificant compared to natural variation and hence there should be no real effect of HFCs on stratospheric ozone. The theory that HFCs could modify stratospheric temperature sufficiently to accelerate ozone loss to a material extent there is based wholly on out-of-date scenarios.

More recently, for a revised high-growth HFC scenario [4], the total projected impact on globally averaged total ozone from HFCs remains less than 0.1 DU (Dobson unit) by 2050 [5]. To put this in context, the ozone layer’s average thickness is about 300 Dobson Units [6], and the natural variability is larger [7].

The Scientific Assessment Panel 2018 Report [8] states that “Outside the Antarctic, CO2, CH4, and N2O will be the main drivers of stratospheric ozone changes in the second half of the 21st century, assuming full compliance with the Montreal Protocol. These gases impact both chemical cycles and the stratospheric overturning circulation, with a larger response in stratospheric ozone associated with stronger climate forcing.”

Sources:

  1. Ravishankara A. R., A.A. Turnipseed, N.R. Jensen,.S. Barone, M. Mills, C.J. Howard and S. Solomon (1994), Do Hydrofluorocarbons Destroy Stratospheric Ozone?, Science, 263, 71–75,doi:10.1126/science.263.5143.71
  2. Hurwitz M. M., E.L. Fleming, P.A. Newman, F. Li, E. Mlawer, K. Cady-Pereira and R. Bailey (2015), Ozone depletion by hydrofluorocarbons, Geophys. Res. Lett., 42, doi:10.1002/2015GL065856.
  3. Velders, G. J. M., D. W. Fahey, J. S. Daniel, M. McFarland, and S. O. Andersen (2009), The large contribution of projected HFC emissions to future climate forcing, Proc. Natl. Acad. Sci. U.S.A., 106(27), 10,949–10,954.
  4. Velders, G.J.M., D.W. Fahey, J.S. Daniel, S.O. Anderson, and M. McFarland, Future atmospheric abundances and climate forcings from scenarios of global and regional hydrofluorocarbon (HFC) emissions, Atmos. Environ., 123 (A), 200−209, doi:10.1016/j.atmosenv.2015.10.071, 2015.