6 October 2015
By Larry O’Hanlon
Something strange has happened to the atmospheric concentration of a newly discovered, human-made, ozone-destroying gas: it has suddenly dropped and nobody knows why.
The gas, HCFC-133a, is a type of hydrochlorofluorocarbon, ozone-destroying compounds used in some industrial processes, including the manufacturing of refrigerants. The use of HCFCs, which are also powerful greenhouse gases, is restricted under the Montreal Protocol. A study last year first identified HCFC-133a as one of four previously undetected human-made gases in the atmosphere that are contributing to destruction of the ozone layer, but the source of HCFC-133a remains a mystery.
New measurements show that after a rapid increase of the compound in the atmosphere of the Northern Hemisphere from 0.13 parts per trillion (ppt) in 2000 to 0.50 ppt in 2013, the concentration suddenly dropped to about 0.44 ppt by early 2015. This drop in concentration is equivalent to a 50 percent decline in global emissions percent of the gas: from 3,000 metric tons (3,300 US tons) in 2011 to about 1,500 metric tons (1,700 tons) in 2014, according to the new study.
“This is enormous, how quickly the trend reversed,” said Martin Vollmer of the Swiss Federal Laboratories for Materials Science and Technology in Dubendorf, Switzerland. But instead of deepening the mystery of HCFC-133a’s sources, the abrupt change offers new clues, Vollmer said.
“That change tells us a lot,” said Vollmer, the lead author on a new paper reporting the findings, which has been accepted for publication in the AGU journal Geophysical Research Letters (the paper is available here). If the compound was being installed in a refrigerator or as foam in seat cushions, it would be leaking out slowly over time and the concentration in the atmosphere would not have changed so quickly, he said. “So this has to be something that humans have immediate control of,” Vollmer said.
The new findings by Vollmer and his colleagues suggest that the source of HCFC-133a is the mass production of another gas, HFC-134a, which is an ozone-friendly refrigerant used in automobile air conditioners. It is known that when you make HFC-134a, the ozone-destroying HCFC-133a is an intermediate product, Vollmer said. And since HFC-134a is being mass produced, it’s a likely source for leaking HCFC-133a into the atmosphere, he said.
“That’s most likely the biggest source of HCFC-133a currently,” Vollmer said. “But it’s not known how much leaks out. We expected HCFC-133a to grow rapidly in the atmosphere because of the enormous and growing global demand and production of HFC-134a, but we found the opposite. One of our speculations is that there are one, two or three factories that have been grossly emitted HCFC-133a but were cleaned up.”
The changes in HCFC-133a were discovered because of continuous air sampling underway at stations around the world to detect a wide range of human-made trace gases. The same system was used recently to detect the rise in surgical anesthetics (see the press release), which are also greenhouse gases.
– Freelance science journalist Larry O’Hanlon acts as AGU’s blogs manager and social media coordinator.