Other atmospheric breakdown products

The final atmospheric breakdown products of HFCs, HFOs and HCFOs can include depending on the specific substance:

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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.  [A large and ubiquitous source of atmospheric formic acid, D. B. Millet et al, Atmos. Chem. Phys., 15, 6283–6304, 2015 www.atmos-chem-phys.net/15/6283/2015/doi:10.5194/acp-15-6283-2015]. Formic acid generated from HFCs and HFOs is negligible.

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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) [1] [2] [3].

[1] EFCTC Learn about environment & breakdown products: Fluoride in the Atmosphere: A very small contribution from HFCs, https://www.fluorocarbons.org/wp-content/uploads/2020/07/EFCTC_Learn_about_Fluoride_in_atm_small_HFC_contribution.pdf.

[2] Friend, J.P., (1989) Scientific Assessment in the AFEAS Report- Chapter 11, Natural Sources. Natural chlorine and fluorine in the atmosphere, water and precipitation.

[3] 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

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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 CO2from HFC, HFOs and HCFOs is negligible.

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Chlorides

Most of the HCl in the lower atmosphere (where acid rain is generated) is the result of acidification of sea salt aerosol [4]. 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. Chloride from HCFOs is negligible.

[4] 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