Sulfur hexafluoride (SF6) is not nearly as infamous as CO2, with the latter getting most of the blame for anthropogenic climate change. Yet while measures are being implemented to curb the release of CO2, for SF6 the same does not appear to be the case, despite the potentially much greater impact that SF6 has. This is because when released into the atmosphere, CO2 only has a global warming potential (GWP) of 1, whereas that of methane is about 28 over 100 years, and SF6 has a GWP of well over 22,000 over that same time period.
Also of note here is that while methane will last only about 12.4 years in the atmosphere, SF6 is so stable that it lasts thousands of years, currently estimated at roughly 3,200 years. When we touched upon sulfur hexafluoride back in 2019 in the context of greenhouse gases, it was noted that most SF6 is used for — and leaks from — high-voltage switchgear (mechanical switches), transformers and related, where the gas’ inert and stable nature makes it ideal for preventing and quenching electrical arcing.
With the rapid growth of highly distributed energy production in the form of mostly (offshore) wind turbines and PV solar parks, this also means that each of these is equipped with its own (gas-filled) switchgear. With SF6 still highly prevalent in this market, this seems like an excellent opportunity to look into how far SF6 usage has dropped, and whether we may be able to manage to avert a potential disaster.
However, this only tells part of the story. Carbon dioxide is not alone in its role as a greenhouse gas, with many others contributing significantly to global temperature rises. As humanity struggles to keep warming below 2 degrees C over the century, strategies will be needed to tackle the problem on all fronts.
There’s A Bad Smell Around Methane
Methane is a remarkably potent greenhouse gas, having 28 times the warming potential of CO2 by weight over a 100-year period. Historically, it’s mostly been released from natural sources, like bacteria processing organic material in stagnant watercourses, or from thawing permafrost. However, scientists now consider around 60% of methane in the atmosphere to be a direct result of human activity.
Agriculture is a major contributor in this area. Ruminant animals raised for human consumption are major methane emitters, as the microbes in their digestive systems release the gas when breaking down plant material. With the demand for meat and dairy showing no signs of slowing down, this could prove difficult to tackle. There are a variety of other diffuse sources of the gas, too. Landfills and sewage plants have significant methane emissions of their own, and it’s also often released from oil and gas drilling operations, too.
Levels of methane in the atmosphere have been low compared to carbon dioxide. Methane also tends to have a short life in the atmosphere, of around 9 years. These factors have meant that methane has historically been of lower concern to environmental organisations. However, after levels plateaued from the 1990s to the mid-2000s, they have once again begun to climb precipitously. Scientists have yet to identify the cause of this rise, and it has the potential to undo hard-fought gains in the fight against global warming on the CO2 front. Theories range from a reduced level of chemicals that break down methane in the atmosphere, to increased livestock production or the rise of the hydraulic fracturing industry.
Nitrous oxide isn’t just the favorite gas of the Fast and the Furious. It’s also a potent greenhouse gas, with 300 times the warming potential of carbon dioxide, pound for pound. With plenty of staying power, it sticks around in the atmosphere for 114 years on average. With 40 percent of NOx emissions coming from human activity, it’s a significant player as far as greenhouse gases go.
Fertilizer use in agriculture is the major contributor to nitrous oxide releases into the atmosphere. As farms push for ever-greater yields, there has been a corresponding increase in the use of nitrogen-containing fertilizers. Other lesser sources include fossil fuel combustion and various chemical production processes.
Reducing nitrous oxide emissions to any major degree is a difficult problem. Reducing farm yields is impractical if we wish to continue feeding as many people as possible. Increasing the efficiency of fertiliizer application is instead a more viable way to go. By applying fertilizers in the right way, in the right quantities at the right time, has the benefit of both reducing nitrous oxide emissions as well as cutting costs for farming operations. Other gains in this space can be made by reducing fossil fuel use by switching to renewable energy production, or cleaner burning technologies. The famous catalytic converter, introduced to gasoline-powered vehicles in the 1970s, plays a major role in reducing these emissions, and urea injection does much the same for diesel engines, which we’ve talked about before.
Sulfur Hexa-what now?
Recently, sulfur hexafluoride has come under scrutiny. Also known by its chemical formula, SF6, it’s a highly potent greenhouse gas, with a warming potential of over 23,000 times that of CO2. Prized for its performance as a gaseous dielectric medium, it’s used heavily in high-voltage circuit breakers in modern electricity grids. It enables the construction of much more compact switchgear, while remaining safe and reliable in operation.
Concentrations of SF6 have begun to tick up in recent times, raising alarm bells. Speculation is that this is down to leaks of the gas from electrical equipment. As the world’s energy mix changes, grids have come to rely on more distributed generation, from sources like wind farms and solar. This mode of generation necessitates many more connections to the grid, which means more switchgear, and thus more SF6 out in the wild.
Work is afoot to slow this trend before things get out of hand. A replacement has been developed in a collaboration between ABB and 3M, by the name of AirPlus. While the production process releases more CO2, over the lifecycle of an installation, AirPlus-based switchgear should have far lower impact on warming. This is due to the fact that when released into the atmosphere, AirPlus degrades under UV light exposure in just 15 days, versus 3200 years for SF6. Its global warming potential is less than 1, meaning it has less of a warming effect than even CO2, while delivering comparable dielectric performance to SF6. Variants are available for both medium and high voltage applications.
Over time, as goverments work to reduce the prevalance of SF6 in new installations, its likely that we’ll see AirPlus and other alternatives gain steam. The gas has already been banned in the EU for all non-electrical purposes, since 2014. Industry is typically slow to act unless there’s a strong business case, so government intervention is likely to be the game changer that pushes adoption of newer, cleaner technology in this space.
Other Fluorinated Gases
SF6 is just one of a series of fluorinated gases that have significant global warming potential. Many of these were introduced as replacements for chlorofluorocarbons (CFCs), which tend to eat a hole in the ozone layer. Thankfully, that problem was largely solved when production of CFCs was tailed off in 1996, but their replacements can still cause further troubles.
With lifetimes in the hundreds to thousands of years in the upper atmosphere, gases like hydrofluorocarbons and perfluorocarbons have an outsized effect on atmospheric warming, thousands of times that of CO2 on a per-molecule basis. They have applications as aerosol propellants, solvents, and fire retardants, but their primary use is as refrigerants in cooling systems. HFC-134a is the most well-known, used widely in air conditioning systems worldwide, and particularly in motor vehicles. This has led to its position as the most abundant HFC in the atmosphere.
Efforts are in place to limit the impact of these chemicals, through precautionary measures. This involves taking more care during the repair and disposal of HVAC systems, as well as designing systems to be more resilient of leaks in the first place. Recycling methods are also beneficial to ensure that where possible, these gases are captured rather then simply vented to the atmosphere. Enforcement on a broad scale remains a challenge.
Sometimes, it’s better to avoid the problem entirely. A transition away from using refrigerants like HFC-134a is in progress. The EPA has legislated that all light vehicles manufactured or sold in the USA by model year 2021 must no longer use HFC-134a. Instead, alternatives like HFO-1234yf, HFC-152a, and R-744 will be legal. The first two are mildly flammable, while the latter is simply another name for good old CO2. These refrigerants will require different technology to existing air conditioners. CO2-based systems in particular needing to operate at up to 10 times the pressure of traditional systems. However, progress in technology should allow these gases to take over, reducing the impact these refrigeration gases have on global warming.
The Fight Continues
CO2 is still the primary greenhouse gas, but it’s not the whole story. We’ve looked at a wide variety of chemicals, each with their own important roles and impact on the Earth’s atmosphere. This highlights the fact that there’s no single panacea to heading off global warming; instead, a broad spectrum approach across all aspects of human endeavour is required.
Halting the impacts of these chemicals is difficult, and will require decisive action by both government bodies, as well as cooperation from relevant industries. In some cases, there are additional gains to be had, while in others, the solution comes with high costs and painful changes. We engineered ourselves into this situation, so we can probably engineer ourselves out. Regardless, if humanity is to flourish in the next century, there remains much work to be done.
As the global climate emergency continues to loom over human civilization, feverish work is underway around the world to find technical and political solutions to the problem. Much has been gained in recent years, but as global emissions continue to increase, there remains much left to do to stave off the most catastrophic effects of climate change.
Renewable energy has led the charge, allowing humanity to continue to enjoy the wonders of electricity with a reduced environmental impact. The future looks promising, with renewable sources becoming cheaper than traditional fossil fuel energy plants in many cases, both in the USand abroad. At the same time, the rise of renewable technologies has brought new and varied challenges to the fore, which must be dealt with in kind. Take wind energy, for instance. Continue reading “What Will We Do With The Turbine Blades?”→