15.5: Mitigating Hydrofluorocarbons (HFCs)

Hydrofluorocarbons (HFCs) are factory-made gases that are SLCPs with comparatively short lifetimes in the atmosphere. They are super climate pollutants with high global warming potentials. They were invented as substitutes for chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), two groups of chemicals that destroyed the protective stratospheric ozone layer and warmed the climate. CFCs were phased out under the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer, and HCFCs are currently being phased out under that treaty. The phaseout of these and related chemicals under the Montreal Protocol has put the stratospheric ozone layer on the path to recovery, with noticeable improvements to the ozone layer expected by the 2030s and closing of the Antarctic ozone hole expected by 2060.

While they do not destroy stratospheric ozone as the CFCs and HCFCs they replaced did, HFCs are the fastest-growing climate pollutant in many countries, and many HFCs have high global warming potentials (GWPs). Because of the climate risk posed by the fast-growing HFCs, a small group of countries began an 8-year effort to phase down HFCs under the Montreal Protocol, culminating in the Kigali Amendment in October 2016, which will take the single biggest bite out of the climate problem so far. Phasing down HFCs has the potential to avoid up to 0.5ºC of warming by 2100, and the initial phasedown schedule of the Kigali Amendment will deliver 80%. Getting the remaining 20% will require speeding up the schedule or otherwise encouraging countries to avoid moving into HFCs during their current phaseout of HCFCs—a leapfrog strategy whereby countries move directly into climate friendly substitutes. (Unlike the earlier phaseouts, the Kigali Amendment is a phasedown because some HFCs have very low GWPs; for example, HFC-1234yf, a refrigerant used in mobile air conditioners, has a GWP of only 1.)

Table 15.5.1 The most commonly used HFCs according to Montzka et al. 2015, with GWPs and lifetimes from the IPCC Fifth Assessment Report

HFC	GWP (100-Year)	Lifetime (Years)
HFC-134a	1,300	13.4
HFC-152a	138	1.5
HFC-143a	4,800	47.1
HFC-125	3,170	28.2
HFC-32	677	5.2
HFC-227ea	3,350	38.2
HFC-365mfc	804	8.7

Source: Montzka, S. A., et al. 2015. Recent trends in global emissions of hydrochlorofluorocarbons and hydrofluorocarbons: reflecting on the 2007 adjustments to the Montreal Protocol. Journal of Physical Chemistry 119, 4439–4449; IPCC. 2013. 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., et al. (eds.)]. Cambridge University Press, New York, NY.

HFC impacts

HFCs were developed in the 1990s and started to replace CFCs and HCFCs in refrigerators, air conditioners, insulating foams, and other uses. As noted, HFCs are the fastest-growing climate pollutant in many countries, and while their climate impact in 2010 was relatively small, they were projected to increase 30-fold by 2050 if not mitigated through the measures discussed in this section.

The average lifetime of HFCs currently in use is 15 years, but their high GWPs (some are almost 5,000 times more potent than CO₂) mean they have a large impact on the climate in that short time. Unchecked, annual HFC emissions could have the global warming equivalent of 12% of annual CO₂ emissions in 2050 under a business-as-usual scenario, and up to 71% under the strongest of IPCC mitigation scenarios. Additionally, continued manufacture of appliances and foams that utilize HFCs will lead to storage of these pollutants in what are called HFC banks, which will emit HFCs as the products are discarded and will contribute to further warming.

HFC sources

HFCs are used in refrigeration, air conditioning, thermal insulating foam blowing, aerosol sprays, fire protection, and solvents. As an example, in the United States, air conditioning and refrigeration make up 86% of the country’s HFC emissions; this includes commercial refrigeration, mobile air conditioning in cars and other vehicles, and stationary air conditioning in homes, offices, and other buildings. The remaining emissions come from residential and industrial refrigeration, transport refrigeration, aerosol propellants, and solvents.

At what point during their life cycle HFCs are emitted depends on how they are being used. For aerosols and solvents, HFCs are emitted while in use. For foams, HFCs are emitted during the manufacturing process, when they leak out of foam in use as building insulation (off-gas), and when the foam is crushed for disposal later or when it is otherwise damaged. For HFCs used in refrigerators and air conditioners, emissions occur throughout a product’s lifetime, including during manufacture, while the appliance is in use, during servicing, and at the end of the appliance’s life.

HFC mitigation

Many developed countries have already begun the transition to lowGWP HFCs and non-HFC alternatives, and as developing countries move away from HCFCs, they can leapfrog HFCs to the more climate-friendly alternatives to maximize climate benefits. This leapfrog strategy also helps avoid the buildup of the banks of HFCs in air conditioners, foams, and other products, with the potential to avoid another 53 gigatons of CO₂ equivalent (CO₂eq) between 2020 and 2060.

Alternatives to high-GWP HFCs are readily available for most uses, ensuring a smooth transition (Table 15.5.2). Alternatives include lowGWP HFCs like R-32 with a GWP of 660 and extremely low-GWP HFCs sometimes called hydrofluoroolefins (HFOs), natural refrigerants, and not-in-kind alternatives. For example, HFC-134a, with a GWP of 1,300, has been the most commonly used refrigerant in mobile air conditioners and is quickly being replaced in developed countries by HFO-1234yf, with a GWP of less than 1.

Table 15.5.2 Indicative list of low-GWP alternatives to high-GWP HFCs

Application	Current Refrigerant	GWP	Alternative	GWP
Refrigeration (domestic)	HFC-134a HFC-152a	1,300 138	HC-600 (isobutene) HC-290 (propane) HFO-1234yf	~3 <5 <1
Refrigeration (commercial & industrial)	HCFC-22 HFC-407C HFC-134a HFC-404a	1,760 1,774 1,300 3,943	HC-600 (isobutene) R-744 (CO2) R-717 (ammonia) HFCs and HFC blends	~3 1 0 <1–1,600
Air conditioners (room)	HFC-410A HCFC-22 HFC-407C	1,923 1,760 1,774	HC-290 (propane) HFC-32 HFC/HFC blends emerging	<5 677 ~350
Air conditioners (commercial)	HFC-134a HCFC-22 HCFC-123	1,300 1,760 79	HFO-1233zd HFO-1234ze HFC/HFC blends emerging HFO-1234yf	<1 <1 400–500 <1
Mobile air conditioners	HFC-134a	1,300	HFO-1234yf HFC-152a R-744 (CO2) R-290 (propane)	<1 138 1 <5
Foams	HFC-227ea HCFC-142b HFC-245fa HCFC-22HFC-134a	3,220 1,980 1,030 1,810 1,300	HCs CO2/water HFO-1234ze Methyl formate HFO-1336mzz-Z	<5 1 <1 <25 2

Natural refrigerants include ammonia (GWP near 0), hydrocarbons like propane and isobutene (GWPs less than 5), and CO₂ (GWP of 1). Commercial refrigeration has moved to these low-GWP alternatives, with up to 65% of new installations already using them. Domestic refrigeration could see about 75% of production using natural refrigerants by 2020. Some room air conditioners are also using hydrocarbons as alternatives, although such natural refrigerants tend to be more flammable, which presents safety concerns and in some circumstances limits their use to smaller appliances. Not-in-kind alternatives include methods of cooling that do not involve chemical refrigerants, such as improving building insulation and implementing reflective roofs.

The mandated transitions of refrigerants from CFCs to HCFCs and then to HFCs catalyzed energy efficiency improvement of the cooling equipment, and the Kigali Amendment’s mandated transition from HFCs to more climate-friendly alternatives presents another opportunity to further improve efficiency. When selecting among alternatives, it is important to consider energy efficiency, as the electricity used to run cooling equipment can be up to 90% of the total carbon footprint when fossil fuel is the source of the electricity. It also is important to consider safety issues, like the flammability associated with natural refrigerants.

Even before the Kigali Amendment was agreed, some leading countries began taking steps to phase down HFCs, including economic and market-based incentives, required practices, import/export licensing, reporting requirements, and taxes and fees. For example, the US has a number of regulations relating to HFCs, curtailing the applications where they may be used. The EU has regulated HFCs for over a decade, strengthening the regulations over time to more aggressively phase down HFCs. Norway instituted a tax-and-refund scheme where a tax was levied on the import of HFCs but was refunded upon proper disposal of the refrigerant. In the US, some states, including California, also restrict HFC use.