Select Page

Atmospheric Degradation products – indirect GWPs

Degradation of HFCs, HFOs and HCFOs has been extensively investigated by laboratory research and atmospheric modelling.

The hydroxyl radical (OH) is the primary reactive agent of the lower atmosphere (troposphere) and, in particular, it provides the dominant initial reaction of HFCs, HFOs and HCFOs. The HFOs and HCFOs have a double bond and a minor reaction with ozone in the atmosphere can also occur. Initial reactions can result in the formation of intermediate degradation products, and these react further resulting in final degradation products. The yields and properties of intermediate and final degradation products in the atmosphere are generally well understood, but with some uncertainties, although further research continues to improve the overall analysis. Two degradation products are particularly important.

These are trifluoroacetic acid (TFA) and trifluoromethane (HFC-23, CF3H). TFA is the terminal breakdown product of some HFCs, HFOs and HCFOs [1]. HFC-23 was not detected [2], with an upper limit of 0.3% yield from photolysis of CF3CHO (trifluoroacetaldehyde-an intermediated formed from some HFCs, HFOs and HCFOs) and directly in minor yields from some HFOs by reaction with ozone [3]. HFC-23 has a long atmospheric lifetime (228 years) and a very high GWP (14800 AR4 F-gas 2024/573 value), but eventually degrades to CO2 and HF. Important recent publications about atmospheric degradation to TFA and HFC-23 are references [1 to 5]. The table Major HFC, HFO and HCFOs: Atmospheric degradation in the troposphere – intermediates and final products also has CF3H and TFA yields where applicable, and references.

Atmospheric degradation of CF3CHO

According to the 2022 Assessment Report of the Environmental Effects Assessment Panel (EEAP 2022) [1] CF3CHO has three competing fates in the atmosphere.

  • Current understanding of the atmospheric fate of CF3CHO suggests that its atmospheric fate is dominated by destruction by photolysis resulting in an atmospheric lifetime of the order of two days, giving CF3 and HCO radicals, which cannot contribute to the formation of TFA.
  • Second, oxidation initiated by OH. The rate of reaction of CF3CHO with OH radicals is slow (atmospheric lifetime of approximately 20 days), and thus of less importance in the fate of CF3CHO. Any oxidation of CF3CHO initiated by OH radicals will produce CF3CO radicals, which undergo reaction with O2 to yield acyl peroxy radicals, CF3C(O)O2. These acyl peroxy radicals can react with HO2, NO, or NO2. Reaction of CF3C(O)O2 with HO2 radicals can lead to the formation of TFA (39% yield) as a minor product.
  • Third, contact with liquid water produces hydrates, which can react with OH radicals leading to the formation of TFA, however, the importance of hydrolysis of CF3CHO to give TFA is highly uncertain. Assuming that uptake into cloud water and hydration is efficient, effectively converting CF3CHO into TFA on a timescale of 5 days (only limited by transport limitations, i.e., the lower limit for the time taken for transport into clouds then a maximum TFA yield of 27% can be expected from the hydrate formation.

According to EEAP 2022, the latter two processes are currently thought to be minor fates of CF3CHO. The importance of formation of TFA from the reaction of OH with CF3CHO was indirectly accessed by Sulbæk Andersen et al. [4] in a global modelling study of HCFO-1233zd. This model, which did not include potential CF3CHO-hydrate formation, suggested a 2% yield of TFA from CF3CHO. Overall, EEAP 2022 in section SI 4.1.3 states “Thus, the TFA yield from processing of CF3CHO is estimated at 2% with an upper theoretical limit of ~ 30%.” The EEAP 2022 conclusions for TFA (section 3.8) states “With the transition from HFCs to HFOs, the importance of the degradation product, CF3CHO, in the environment is increasing. Nevertheless, CF3CHO is likely to be only a minor source of TFA.”A 2024 publication [5], by members of the Environmental Effects Assessment Panel provides an update on the chemistry of precursors to TFA related to chemicals under the purview of the Montreal Protocol, commenting that “A recent modelling study using updated atmospheric photolysis coefficients of CF3CHO gives a photolytic lifetime for CF3CHO of 13 ± 4 days (at 5 km altitude in the tropics), which is significantly longer than the previous estimate of 2–3 days. Further studies are needed to confirm these findings. However, a longer photolytic lifetime would translate into higher molar yields of TFA from CF3CHO and increase the potential importance of interaction of CF3CHO with liquid water in the atmosphere.

EFCTC comment on the hydration of CF3CHO

The hydration of CF3CHO produces CF3CH(OH)2 in a reversible reaction in the atmosphere, but this requires contact with water-rich media such as clouds.

A typical lifetime for uptake into aqueous droplets is about 15 days [4]. Homogeneous gas-phase reaction with H2O occurs slowly, if at all. The CF3CH(OH)2 if available in the atmosphere can react with hydroxyl radicals leading to TFA in 100% yield. This reaction is slow with an estimated atmospheric lifetime for reaction of CF3CH(OH)2 with OH of approximately 90 days [6]However, as the CF3CHO and CF3CH(OH)2 are in equilibrium, the assumption that CF3CHO once hydrated goes to 100% TFA cannot be substantiated. The 90 days lifetime for reaction of CF3CH(OH)2 with OH is long enough to allow competition from the likely dehydration under low humidity conditions and subsequent fast loss via photolysis. Therefore, the probability of CF3CH(OH)2 dehydration to CF3CHO under low humidity conditions and subsequent photolysis suggest that the hydration path may not contribute significantly to TFA formation. It should be noted that the equilibrium constants and their dependence on temperature are not known [7].

Reaction of HFOs and HCFOs with ozone

The presence of an olefinic bond (C=C bond) in HFOs and HCFOs results in their relatively rapid reaction with hydroxyl (OH) radicals present in the atmosphere, leading to short atmospheric lifetimes measured in days or weeks and small direct global warming potentials.

However, the olefinic bond also allows minor reaction with ozone (ozonolysis), and whilst these reactions are slow, McGillen et. al. [8] report that HFC-23 may be produced in very small yields from some HFOs/HCFOs. According to McGillen et. al. no HFC-23 is formed from HFO-1234yf.  The paper accounts for this process in atmospheric chemical and transport modelling simulations and reports the indirect global warming potentials due to the formation of HFC-23. The results reported in the paper are summarised in the table below. The calculated indirect GWPs due to HFC-23 formation are also shown in the table. It is worthwhile noting that some hydrocarbon refrigerants have indirect GWPs [9] of similar magnitude (propane, 9.50; n-butane, 6.5). All of these refrigerants (HFOs, HCFOs and HCs) are classified as ultralow GWP refrigerants (0-30 GWP) [10]. The ozonolysis experiments for HFO-1234yf also showed no formation of CF4 which might, potentially, have been formed by a similar mechanism to HFC-23 (CF3H) formation for some HFOs.

Yields of HFC-23 from HFOs and HCFOs via ozonolysis

SubstanceStructureDegradation via ozonolysisYield of HFC-23 from ozonolysis routeOverall yield of HFC-23 from HFO/HCFOIndirect GWP due to HFC-23Direct GWP AR6
HFO-1234yfCF3CF=CH20%0%00.50
HFO-1234ze(E)CF3CH=CHF2.96%3.11%0.092%~ 121.37
HFO-1336mzz(Z)CF3CH=CHCF30.13%0.42%0.0005%<0.12.08
HCFO-1233xfCF3CCl=CH20%0%04
HFO-1243zfCF3CH=CH21.25%0.37%0.0046%<10.26

a: atmospheric modelling results.
b: experimental measurements.

Explanatory notes for the table

The yields of HFC-23 following reaction with ozone (ozonolysis) are experimental measurements. The percentage of degradation by reaction with ozone route is calculated from atmospheric modelling simulations, with the main degradation route being the reaction with hydroxyl (OH) radical. The indirect GWP due to HFC-23 formation in this table is taken from Fig.4 of the paper. The supporting information for the paper explains that the GWP was calculated for each HFO under consideration and also for CHF3. The calculated direct GWPs for the HFOs in Fig.4 of the paper are slightly different from the 100 year AR6 GWP values, which are included in the table for completeness. HCFO-1233xf and HFO-1243zf are not used commercially as refrigerants but are used in the study due to their molecular structure to improve understanding of the mechanism and structural effects.

Properties of intermediate and final degradation products

The properties of intermediate substances formed during the degradation of HFCs, HFOs and HCFOs are in the table below.

IntermediateAtmospheric Lifetime [11]GWP-100 [11]Comment
COF27 days (5–10 days)<1Heterogeneous processing [physical removal] is the predominate removal process in the troposphere by hydrolysis to HF and CO2.
CF3CHO2.7 days<<1See section Atmospheric degradation of CF3CHO.
HCFOHC(O)F has a short atmospheric lifetime with hydrolysis to HF and CO2 and is not expected to contribute to radiative forcing. Heterogeneous processing [physical removal] is the predominate removal process in the troposphere. See WMO 2010 Section 5.4.3.2 [12].
CF3OH<<1 dayUptake of CF3OH into aqueous solutions leads to rapid hydrolysis to form HF, CO2, or CF2O, giving rise to large uptake coefficients on atmospheric aerosols containing water. According to Lovejoy et al.,1b heterogeneous loss on cloud particles will be a very efficient sink for CF3OH in the troposphere (t = 0.05 day) on the basis of their measured uptake parameters. [13][14]
CF3CFO6.9 days<<1Hydrolysis to TFA.
CF3COCF318 days3Tropospheric photolysis to give CF3 and CF3CO radicals. [15]
HCClO5–15 days [15]EEAP 2022 figure 11 [15]

Degradation in the stratosphere

Hydrofluoroolefins (HFOs) are substances with lifetimes of days to weeks, which is much shorter than the time scale for mixing between the hemispheres and transport to the stratosphere. They are not well mixed in the troposphere their short lifetimes effectively reduce the fraction of their emission reaching the stratosphere and their accumulation in the atmosphere as compared to the longer-lived HCFCs and HFCs [11]. 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. The HFOs are very short lived substances (VSLSs), defined as trace gases whose local lifetimes are shorter than 0.5 years [12]

Hydrofluoroolefins (HFOs) are substances with lifetimes of days to weeks, which is much shorter than the time scale for mixing between the hemispheres and transport to the stratosphere. They are not well mixed in the troposphere their short lifetimes effectively reduce the fraction of their emission reaching the stratosphere and their accumulation in the atmosphere as compared to the longer-lived HCFCs and HFCs [11]. 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. The HFOs are very short lived substances (VSLSs), defined as trace gases whose local lifetimes are shorter than 0.5 years [12]

  • Degradation of CF3CFO in the stratosphere: CF3CFO is formed as an intermediate degradation product mainly from HFO-1234yf (100% yield), HFC-134a (7-20% yield) and HFC-227ea (100% yield) [13]. In the troposphere, its lifetime is 6.9 days[14] and it is hydrolysed to TFA and rained out. Due to its short lifetime, HFO-1234yf degradation occurs predominantly in the troposphere, with losses in the stratosphere, typically accounts for only a small fraction of total losses [15]. According to Jubb et al. [16], for HFC-134a, some CF3CFO degradation occurs in the stratosphere, where photolysis results in very low quantum yields of the PFC-14, CF4. According to Jubb et al., overall, the CF4 quantum yields for CF3CFO photolysis at stratospherically relevant wavelengths (<220 nm) are small with the greatest value of (75 ± 1) × 10-4 obtained at 193 nm and noting that the photodissociation of CF3CFO is strictly a stratospheric loss process. In the lower stratosphere, the CF3CFO photolysis lifetime is sufficiently long, on the order of years, that transport out of this region is an important removal process that is accounted for in Jubb et al. atmospheric model. Assuming a maximum yield of 20% CF3CFO for HFC-134a degradation, the CF4 production per molecule of HFC-134a emitted into the atmosphere was 2.5 × 10-5 molecules [it is worth noting that this is equivalent to adding 0.18 to the GWP-100 of HFC-134a]. The paper estimated that CF4 produced via CF3CFO photolysis, due to HFC-134a degradation, was about 5 tonnes in 2020. The Jubb et al. paper forecasts an increase in CF4 from HFC-134a to about ~9 t per year in year 2100. This is insignificant relative to the global CF4 emissions, currently around 15,000 tonnes/yr [17]. This estimate of CF4 from HFC-134a in 2100 was published before the 2016 Kigali Amendment to phase-down HFCs. Very low quantities of CF4 from HFC-227ea degradation via CF3CFO would also be expected. For the very short-lived HFO-1234yf the contribution of CF4 is expected to be even smaller than for HFC-134a [17]

 

  • Degradation of CF3CHO in the stratosphere: Laboratory studies for the degradation of CF3CHO in the troposphere by photolysis did not detect HFC-23 with an upper limit of 0.3% yield [18]. According to the Report of the Scientific Assessment Panel in response to Decision XXXV/7: Emissions of HFC-23 [19], reactive losses of HFCs, HFOs and HCFOs can also occur in the stratosphere, but losses there typically account for only a small fraction of total losses. Different conditions present in the stratosphere (total pressure, temperature, UV flux, CF3CHO photolysis lifetime, etc.) could affect overall yields and estimated production rates for HFC-23, but a lack of wavelength dependent and consistent pressure dependent CHF3 product yield measurements limits an evaluation of stratospheric CHF3 production rates at this time. It is worth emphasising that the HFOs and HCFOs are substances with lifetimes of days to weeks, which is much shorter than the time scale for mixing between the hemispheres and transport to the stratosphere.

Final Degradation Products from HFCs, HFOs and HCFOs

The final products in Table “Major HFCs, HFOs and HCFOs: Atmospheric degradation in the troposphere – intermediates and final products” include depending on the specific substance:
  • Trifluoroacetic acid (TFA) 
  • HF (hydrogen fluoride)
  • HCOOH (formic acid)
  • HCHO (formaldehyde)
    • CO2 (carbon dioxide)
    • HCl (hydrogen chloride) from HCFOs

    The insignificant effect of acid (TFA, HF, HCl) generated from HFCs, HFOs and HCFOs on acidification (acid rain) in the EU is discussed here[20]

    Fluorides

    are released into the environment naturally through the weathering and dissolution of minerals, in emissions from volcanoes and in marine aerosols. Decomposition of HFCs, HFOs and HCFOs constitute a much smaller source of fluoride in the global atmosphere. Fluorine, in the form of fluoride ion, is found in many rocks and minerals and most soils. It comprises 0.06% of the Earth’s crust (which, although it does not seem much, is actually about twice the known amount of fossil fuel carbon). Estimates of the annual global release of hydrogen fluoride from volcanic sources through passive degassing and eruptions range from 0.06 to 6 million tonnes/year. Wide distribution in soils means that there is significant natural movement of fluoride through the atmosphere on wind-borne dust particles (estimates vary from 1 to 10 million tonnes/year) [21][22].

    Formic acid (HCOOH)

    is one of the most abundant acids in the atmosphere, with an important influence on precipitation chemistry and acidity. Formic acid (HCOOH) is, along with acetic acid (CH3COOH), the dominant carboxylic acid in the troposphere. Both are major sources of atmospheric acidity, and together they can contribute > 60 % of the free acidity in precipitation in remote areas and > 30 % in more polluted regions [23]. Formic acid generated from HFCs and HFOs is negligible.

    Formaldehyde (HCHO)

    is a short-lived, ubiquitous compound with an atmospheric lifetime on the order of a few hours with respect to photolysis and reaction with OH. It is emitted directly into the atmosphere from a variety of sources. Anthropogenic emissions are ubiquitous, concentrated in urban areas. Biogenic sources include live and decaying plants, biomass burning, and seawater [24]. HFOs are a negligible source.

    Carbon Dioxide (CO2)

    is a breakdown product of a wide range of organic substances in the atmosphere including the hydrocarbons such as propane, butane, and pentane. Compared to the use of fossil fuels the contribution of CO2 from HFCs, HFOs and HCFOs is negligible.

    Chlorides

    Most of the HCl in the lower atmosphere (where acid rain is generated) is the result of acidification of sea salt aerosol. This HCl therefore does not represent additional H+ as it is simply a change of counter-ion from SO4 to Cl. HCl is also emitted to the atmosphere from volcanic sources [25][26] Chloride from HCFOs is negligible.

    • Montreal Protocol on Substances that Deplete the Ozone Layer UNEP 2022 Assessment Report of the Environmental Effects Assessment Panel Chapter 6 and Appendix, SI 4 Estimated molar yields (%) of TFA from ODS replacements. Section SI 4.1.3 discusses CF3CHO, and the degradation of each substance is discussed.  Available at  http://ozone.unep.org/science/eeap ↩
    • Tropospheric photolysis of CF3CHO, M. P. Sulbaek Andersen and O. J. Nielsen, Atmos. Environ., 2022, 272, 118935. Tropospheric photolysis of CF3CHO – ScienceDirect ↩
    • Ozonolysis can produce long-lived greenhouse gases from commercial refrigerants, Max R. McGillen, Zachary T. P. Fried, M. Anwar H. Khan, Keith T. Kuwata, Connor M. Martin, Simon O’Doherty , Francesco Pecere, Dudley E. Shallcross, Kieran M. Stanley , and Kexin Zhang, PNAS 2023 Vol. 120 No. 51 e2312714120, https://doi.org/10.1073/pnas.2312714120 ↩
    • Atmospheric Degradation of Ozone Depleting Substances, Their Substitutes, and Related Species, James B. Burkholder, R. A. Cox, and A. R. Ravishankara, Chem. Rev. 2015, 115, 3704−3759, DOI: 10.1021/cr5006759, see section 7.1.1. ↩
    • Continuing benefits of the Montreal Protocol and protection of the stratospheric ozone layer for human health and the environment. Madronich, S., Bernhard, G.H., Neale, P.J. et al.  Photochem Photobiol Sci 23, 1087–1115 (2024). https://doi.org/10.1007/s43630-024-00577-8, 6.1 Update on the chemistry of precursors to TFA related to chemicals under the purview of the Montreal Protocol ↩
    • Atmospheric Chemistry of Perfluorinated Aldehyde Hydrates (n-CxF2x+1CH(OH)2, x= 1, 3, 4): Hydration, Dehydration, and Kinetics and Mechanism of Cl Atom and OH, Radical Initiated Oxidation, M. P. Sulbaek Andersen, A. Toft, O. J. Nielsen, M. D. Hurley, T. J. Wallington, H. Chishima, K. Tonokura, S. A. Mabury, J. W. Martin, and D. A. Ellis, J. Phys. Chem. A 2006, 110, 9854-9860. ↩
    • Atmospheric Chemistry of n-CxF2x+1CHO (x=1, 3, 4): Mechanism of the CxF2x+1C(O)O2 + HO2 Reaction, Sulbaek Andersen, M.P., Stenby, C., Nielsen, O.J., Hurley, M.D., Ball, J.C., Wallington, T.J., Martin, J.W., Ellis, D.A., Mabury, S.A., 2004. J. Phys. Chem. A 108, 6325–6330 ↩
    • Ozonolysis can produce long-lived greenhouse gases from commercial refrigerants, Max R. McGillen, Zachary T. P. Fried, M. Anwar H. Khan, Keith T. Kuwata, Connor M. Martin, Simon O’Doherty , Francesco Pecere, Dudley E. Shallcross, Kieran M. Stanley , and Kexin Zhang, PNAS 2023 Vol. 120 No. 51 e2312714120, https://doi.org/10.1073/pnas.2312714120 ↩
    • Lifetimes, direct and indirect radiative forcing, and global warming potentials of ethane (C2H6), propane (C3H8), and butane (C4H10), Atmos. Sci. Lett. 2018;19:e804. wileyonlinelibrary.com/journal/asl2 https://doi.org/10.1002/asl.804  Øivind Hodnebrog, Stig B. Dalsøren, Gunnar Myhre, Center for International Climate and Environmental Research-Oslo (CICERO), Oslo, Norway ↩
    • Montreal Protocol on Substances that Deplete the Ozone Layer, UNEP 2022 Report of the Refrigeration, Air-conditioning and Heat Pumps Technical Options Committee 2022 Assessment. Table 3-1: Classification of 100-year GWP levels, available at Technology and Economic Assessment Panel (TEAP) | Ozone Secretariat (unep.org) ↩
    •  Atmospheric Degradation of Ozone Depleting Substances, Their Substitutes, and Related Species, J. B. Burkholder, R. A. Cox, and A. R. Ravishankara, Chem. Rev. 2015, 115, 3704−3759, https://doi.org/10.1021/cr5006759 ↩
    •  SAP 2022:  World Meteorological Organization (WMO). Scientific Assessment of Ozone Depletion: 2022, GAW Report No. 278, 509 pp.; WMO: Geneva, 2022. Section 1.3 Halogenated very short-lived substances. Available at https://ozone.unep.org/science/assessment/sap. ↩
    • IPCC/TEAP Special Report Safeguarding the Ozone Layer and the Global Climate System: Issues Related to Hydrofluorocarbons and Perfluorocarbons Chapter 2 page 153 ↩
    • SAP 2022:  World Meteorological Organization (WMO). Scientific Assessment of Ozone Depletion: 2022, GAW Report No. 278, 509 pp.; WMO: Geneva, 2022. Annex Table A-5. Available at https://ozone.unep.org/science/assessment/sap ↩
    • Report of the Scientific Assessment Panel in response to Decision XXXV/7: Emissions of HFC-23, 15 September 2024, Lead Authors: S. A. Montzka, NOAA Global Monitoring Laboratory, USA; J. B. Burkholder, NOAA Chemical Sciences Laboratory, USA, available here, or from or from  Scientific Assessment Panel (SAP) | Ozone Secretariat (unep.org).  This discusses in detail the yields and formation (flux) of HFC-23 from the photolysis of CF3CHO (and intermediate breakdown product of some HFCs, HFOs and HCFOs) and ozonolysis of some HFOs. ↩
    • Jubb, A.M., McGillen, M. R., Portmann, R. W., Daniel, J. S., Burkholder, J. B.: An atmospheric photochemical source of the persistent greenhouse gas CF4, Geophys. Res. Lett., Volume 42, 2015, Pages 9505-9511, DOI: 10.1002/2015GL066193 ↩
    • SAP 2022:  World Meteorological Organization (WMO). Scientific Assessment of Ozone Depletion: 2022, GAW Report No. 278, 509 pp.; WMO: Geneva, 2022. Section 7.2.5.2. Carbon Tetrafluoride (CF4). Available at https://ozone.unep.org/science/assessment/sap ↩
    • Tropospheric photolysis of CF3CHO, M. P. Sulbaek Andersen and O. J. Nielsen, Atmos. Environ., 2022, 272, 118935. Tropospheric photolysis of CF3CHO – ScienceDirect ↩
    • Report of the Scientific Assessment Panel in response to Decision XXXV/7: Emissions of HFC-23, 15 September 2024, Lead Authors: S. A. Montzka, NOAA Global Monitoring Laboratory, USA; J. B. Burkholder, NOAA Chemical Sciences Laboratory, USA, available here, or from or from  Scientific Assessment Panel (SAP) | Ozone Secretariat (unep.org).  This discusses in detail the yields and formation (flux) of HFC-23 from the photolysis of CF3CHO (and intermediate breakdown product of some HFCs, HFOs and HCFOs) and ozonolysis of some HFOs ↩
    •  Lindley, A. et al., Contribution of Hydrofluorocarbons (HFCs) and Hydrofluoro-Olefins (HFOs) Atmospheric Breakdown Products to Acidification (“Acid Rain”) in the EU at Present and in the Future, Open J. Air Poll, 2019, 8, 81-95. ↩
    • Friend, J.P., (1989) Scientific Assessment in the AFEAS Report- Chapter 11, Natural Sources. Natural chlorine and fluorine in the atmosphere, water and precipitation ↩
    • Environmental impact of magmatic fluorine emission in the Mt. Etna area, S. Bellomo, A. Aiuppa, W.r D’Alessandro, F. Parello, Journal of Volcanology and Geothermal Research 165 (2007) 87–101 ↩
    • A large and ubiquitous source of atmospheric formic acid, D. B. Millet et al, Atmos. Chem. Phys., 15, 6283–6304, 2015 http://www.atmos-chem-phys.net/15/6283/2015/doi:10.5194/acp-15-6283-2015] ↩
    • Regional sources of atmospheric formaldehyde and acetaldehyde, and implications for atmospheric modelling, D.J. Luecken, W.T. Hutzell, M.L. Strum, G.A. Pouliot, Atmospheric Environment, Volume 47, February 2012, Pages 477-490, https://doi.org/10.1016/j.atmosenv.2011.10.005 ↩
    • Erickson III, D.J., and Christophe Seuzaret, C., (1999) A general circulation model based calculation of HCl and ClNO2 production from sea salt dechlorination: Reactive chlorine emissions inventory. Journal of Geophysical Research, 104, 8347– 8372. https://doi.org/10.1029/98JD01384 ↩
    • Lobert, J.M., Keene, W.C., Logan, J.A., Yevich, R., (1999) Global chlorine emissions from biomass burning: Reactive chlorine emissions inventory. Journal of Geophysical Research 104, 8373-8389. https://doi.org/10.1029/1998JD100077 ↩