In what would seem to be a very positive result, the world has experienced a drop in one particular, human-made gas that destroys ozone, HCFC-133a. It is a type of hydrochlorofluorocarbon used in making refrigerants and in other industrial processes.

Researchers at the Swiss Federal Laboratories for Materials Science and Technology in Dubendorf, Switzerland, and elsewhere, wrote a paper on this topic that was recently accepted for publication by the journal Geophysical Research Letters.

The source of HCFC-133a remains somewhat uncertain, although the researchers say their study has found significant clues, according to a release.

According to the new measurements in the study, after a quick uptick of the compound in the Northern Hemisphere's atmosphere from 0.13 parts per trillion (ppt), in 2000--to 0.50 ppt in 2013--suddenly, the amount in the same area of atmosphere dropped to around 0.44 ppt by the start of 2015. This is essentially a decrease of about 50 percent in the gas's global emissions. The new study says that the concentration went from 3,300 U.S. tons in 2011 to around 1,700 tons in 2014, said the release.

"This is enormous, how quickly the trend reversed," said Martin Vollmer of the Swiss Federal Laboratories, in the release. "That change tells us a lot."

According to the study, if the concentration changed so quickly, it must be a result of something that humans have immediate control over, said Vollmer in the release.

The researchers believe that HCFC-133a has its source in mass production of the gas HFC-134a. The latter is ozone-friendly and is used as a refrigerant in vehicle air conditioners. HCFC-133a is already known to be an intermediate product of making that refrigerant, Vollmer said in the release.

The team thinks that one, two or maybe three factories were in the past overly emitting HCFC-133a but have now been cleaned up.

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