Carbon dioxide and methane are notoriously the two most abundant greenhouse gases whose excess atmospheric concentration is the main cause of global warming. We talk about “main cause” because There are also other greenhouse gases thateven if in the order of only a few percent, they are present in the atmosphere and their concentration, like carbon dioxide and methane, continues to increase.
Among these less abundant greenhouse gases exist sulfur hexafluoride with numerous industrial applications, but also with very powerful greenhouse properties.
The characteristics of sulfur hexafluoride
Sulfur hexafluoride is an inorganic molecule with symbol SF6 made up of 1 atom of sulfur (chemical symbol S) to which they are linked 6 fluorine atoms (chemical symbol F). It has numerous applications ranging from metallurgy, semiconductor manufacturing, construction, propulsion, but especially for its electrical insulating capabilities.
Often, like other gases, it is used instead of chlorofluorocarbons (CFCs) which are known to destroy the atmospheric ozone layer and which have therefore been banned from commercial use.
In the gaseous state it is transparent, odourless, non-toxic, non-flammable, essentially one of those gases defined as inert gases. However, it is a very dangerous gas for the environment and, specifically, dangerous in the context of global warming.
Its most relevant property in the context of global warming is to be a greenhouse gas, even 24,000 times more effective than carbon dioxide in blocking the infrared radiation emitted by the Earth, with an average residence time in the atmosphere of 3200 years.
Sulfur hexafluoride is a greenhouse gas 24,000 times more effective than carbon dioxide.
Let us remember that the global warming of our planet is a consequence of the fact that an excess fraction of all the infrared radiation emitted by the Earth is unable to escape through the atmosphere. In fact, it is blocked by greenhouse gases.
Those gases present in the atmosphere that are very efficient in absorbing infrared radiation are called greenhouse gases. The excess of greenhouse gases in the atmosphere is producing excess heat accumulation and therefore an increase in global temperature.
How the atmospheric concentration of SF6 is increasing
The concentration of sulfur hexafluoride in the atmosphere has been monitored since 1997 by the Global Monitoring Laboratory of the National Oceanic and Atmospheric Organization (NOAO). It is measured as a mole fraction, i.e
ratio between the amount of SF6 and the sum of the quantities of substance of all the species present in the mixture (the air sample in our case).
It also happened in the month of May: absolute record of air and ocean temperature values
Since it is a very small fraction, it is expressed in parts per trillion (ppt) where one trillion is equivalent to 1 billion billion.
Over the course of about 26 years, the amount of sulfur hexafluoride tripled from 4 to 12 parts per trillion. Thanks to his little concentration contributes only 3% of the global greenhouse gas effect.
Fortunately, having established its nature as a powerful greenhouse gas, its use was gradually reduced to only the most necessary applicationsensuring that its increase remains limited even if it is still growing today.
How much atmospheric carbon would need to be removed to meet the limit set by the Paris Agreement?
Between past but now discontinued applications of sulfur hexafluoride we remember its use as thermal insulation inside the double glazing and to inflate the tyres. Since its molecule is more voluminous than those of nitrogen and oxygen present in the air, it transpires more slowly through the rubber, ensuring a longer residence time inside the tire.
