Greenhouse gas

Sulphuryl fluoride gas used for fumigation has the potential to contribute significantly to future greenhouse warming, according to US researchers.

Scientists at MIT, the Scripps Institution of Oceanography in San Diego and other institutions are reporting the results of their study of the gas this month in the Journal of Geophysical Research.

Sulphuryl fluoride was introduced as a replacement for methyl bromide, a widely used fumigant that is being phased out under the Montreal Protocol because of its ozone-destroying chemistry. Methyl bromide has been used for insect control in grain-storage facilities, and in intensive agriculture in arid lands where drip irrigation is combined with covering of the land with plastic sheets to control evaporation.

‘Such fumigants are very important for controlling pests in the agricultural and building sectors,’ said Ron Prinn, director of MIT’s Center for Global Change Science. ‘But with methyl bromide being phased out, industry had to find alternatives, so sulphuryl fluoride has evolved to fill the role,’ he added.

Until now, no one knew how long the gas would last in the atmosphere after it leaked out of buildings or grain silos. ‘Our analysis has shown that the lifetime is about 36 years, or eight-times greater than previously thought, with the ocean being its dominant sink,’ Prinn said. ‘So it would become a greenhouse gas of some importance if the quantity of its use grows as people expect.’

For now, the gas is only present in the atmosphere in very small quantities of about 1.5 parts per trillion, though it is increasing by about five per cent per year. Its newly reported 36-year lifetime, along with studies of its infrared-absorbing properties by researchers at the National Oceanic and Atmospheric Administration (NOAA), indicate that, ton for ton, it is about 4,800 times more potent a heat-trapping gas than carbon dioxide.

The gas was detected thanks to the NASA-sponsored Advanced Global Atmospheric Gases Experiment (AGAGE), which is designed to sniff out potential greenhouse and ozone-depleting gases.

‘Unfortunately, it turns out that sulphuryl fluoride is a greenhouse gas with a longer lifetime than previously assumed,’ said Jens Mühle of Scripps. ‘This has to be taken into account before large amounts are emitted into the atmosphere.’