A new study lead by Martin Vollmer of the Swiss Federal Laboratories for Materials Science and Technology has found that after a rapid increase in anthropogenic compound named HCFC-133a (CF3CH2Cl), an ozone destroying gas, the atmospheric abundance and emissions have sharply declined in the past three years. The reason for this sharp drop remains a mystery.
Study authors found that a Northern Hemisphere HCFC-133a increase from 0.13 ppt (dry air mole fraction in parts-per-trillion) in 2000 to 0.50 ppt in 2012–mid-2013 was followed by an abrupt reversal to ∼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," AGU's Larry O’Hanlon writes.
According to O'Hanlon, HCFC-133a was identified in 2014 as 'one of four previously undetected anthropogenic gases in the atmosphere that are contributing to destruction of the ozone layer, but its source remains a mystery'.
“This is enormous, how quickly the trend reversed. But instead of deepening the mystery of HCFC-133a’s sources, the abrupt change offers new clues," Vollmer said.
The new findings 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. And since HFC-134a is being mass produced, it’s a likely source for leaking HCFC-133a into the atmosphere," Vollmer said.
"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 emitting HCFC-133a, but were cleaned up.”
According to authors, sporadic HCFC-133a pollution events are detected in Europe from high-resolution HCFC-133a records at three European stations, and in Asia from samples collected in Taiwan. European emissions are estimated to be <0.1 kt yr−1, although emission hotspots were identified in France.
American Geophysical Union (AGU) - Geospace Blog, article by Larry O’Hanlon published October 6, 2015.
Featured image: False-color view of total ozone over the Antarctic pole. The purple and blue colors are where there is the least ozone, and the yellows and reds are where there is more ozone - October 2015. Credit: NASA / OzoneWatch.