Scientists from the US, the UK and the Netherlands have caught a whiff of a banned gas in the atmosphere, prompting questions about who is emitting it and what it is doing there.
CFC-11 belongs to the cadre of compounds called chlorofluorocarbons (CFCs), infamous for creating a hole in Earth’s ozone layer. These chemicals have long life spans and can persist in the atmosphere for several decades once they get there. In this time, they may reach the upper atmosphere and destroy the ozone.
As a result, all countries agreed to cap their chlorofluorocarbon use and, bit by bit, end its production under the terms of the Montreal Protocol, signed in 1987. As part of the same directives, all countries reportedly stopped producing CFCs and other chlorine-containing gases by 2010.
This should have hastened their removal from the atmosphere.
However, between 2012 and 2016, CFC-11 removal was found to to slowed down by almost 50% – a clear sign that some unidentified or unknown phenomenon is offsetting the gas’s decline.
The problem can be likened to the size of a punctured balloon filled with air. Assuming that the gas leaks out of the balloon at a constant rate, the balloon can remain inflated a bit longer if air is blown into it at the same time.
Johannes Laube, a meteorologist at the Centre for Ocean and Atmospheric Sciences, University of East Anglia, Norwich, who was not involved with the finding, is surprised. “This is quite unprecedented because there is no known natural source of chlorofluorocarbons. So, any new emission has to come from anthropogenic activity,” he told The Wire.
CFCs were first produced in the 1960s as alternatives to substances used as fire extinguishers and propellants at the time. Because they were non-toxic, they became a mainstay of foaming agents, refrigerators and air conditioners, and soon entered widespread use. In less than a decade, their levels in the atmosphere became discernible. But most people didn’t bother because the CFCs seemed to be inert.
Then, in 1974, two American scientists named Sherwood Rowland and Mario Molina realised that this inert nature would allow the gases to persist in the atmosphere for long periods of time, in which they’d be able to reach the upper atmosphere, about 20 km above the ground.
Ultraviolet UV) rays from the Sun can penetrate this part of the atmosphere, and they break up CFC molecules to yield chlorine radicals that gnaw away at the ozone layer.
The discovery of an ozone hole the size of North America impelled all countries to spring in action. Under the Montreal Protocol, all nations agreed to cap their chlorofluorocarbon use until they looked for other alternatives and subsequently end its production. It is one of the earliest science driven international agreement and has been instrumental in protecting the ozone till date.
With limits imposed on the production of chlorine-containing gases, the ozone hole started healing. But the new findings can put this in jeopardy.
Scientists monitoring the air at NOAA were the first ones to notice the anomaly in the annual atmospheric CFC-11 levels. As a part of a larger project, Stephen Montzka’s lab at the agency has been monitoring around 40 chemicals that can influence air quality, climate and the ozone.
“Under the same scheme, we have been measuring the levels of chlorofluorocarbons since the 1970s,” Montzka said. Every week, his team samples the air from 12 sites across the northern and the southern hemispheres. They pressurise the samples within cans and send them to the lab he leads for inspection.
The samples are scanned for traces of CFCs and other gases. Such ongoing analyses have revealed that after CFC production was abolished, other gases of the same category – like CFC-12 and CFC-113 – had begun declining faster. An increased clearance was also observed for CFC-11 till about 2012.
Shortly afterwards, however, its removal rate began to slow down. This didn’t make sense.
The amount of CFC-11 in the atmosphere depends on two factors: “The rate at which the gas is being removed and the rate at which fresh gas is being pumped into the system,” per Montzka. While the CFC-11 removal rate has varied slightly over time, it hasn’t been enough to explain recent changes in its concentration. So the only way the current levels of CFC-11 in the atmosphere could be maintained was if there was a fresh supply.
However, the conclusion that someone might be producing the banned gas is preposterous. So scientists did the math to crack the puzzle one piece at a time. They looked at all other factors that could influence the atmospheric clearance rate, and then calculated the amount of that influence for each factor.
For example, atmospheric changes could affect the transport of CFCs between the lower and upper atmospheres. If a large amount of gas was being transported to the upper atmosphere, where it is destroyed by UV rays, then lower CFC-11 levels will have to be detected closer to Earth’s surface.
Which means despite greater quantities being in the atmosphere, only a small amount will end up being measured. But Montzka said, ‘The changes we found could not account for all variations in CFC-11 levels.”
Another source of imbalance could be buildings and furniture constructed before the 1990s that still contain the gas. If damaged, they could leak what CFC-11 they’ve stored in their body into the atmosphere. But the scientists could not locate property destruction at a rate that matched the observed emissions.
And even if that were the case that buildings and furniture were releasing the banned aerosols, such emissions would have had to be traceable to developed countries, where most such sources exist. But in a separate work, researchers actually registered a decline in CFCs emissions from developed countries.
Instead, they found a new seasonal variation in the amount of CFC-11 detected at their station in Mauna Loa. Specifically, beginning in 2013, researchers have noticed a rise in the amount of CFC-11 in air samples collected from Mauna Loa in the autumn.
During autumn, wind often blows from east Asia towards Hawaii. The air samples collected at this time are rich in pollutants found in the orient. At around the same time in 2013, the expected clearance rate of CFC-11 began falling.
“While these are not direct pieces of evidence, they do carry a lot of weight in support of the argument that fresh emissions are from East Asia,” Harish Gadhavi, an atmospheric scientist at the Physical Research Laboratory, Ahmedabad, told The Wire.
Gadhavi proposed conducting similar analyses from many stations, and more closely scrutinising country-wise emissions to confirm that the unreported CFC-11 emission is from east Asia.
Laube also believes the scientists have covered all bases and that the new CFC-11 emissions are likely of east Asian origin. “The finding is worrying because when chlorine-containing gases are used in industries, only a small fraction escapes into the atmosphere. Since emissions are offsetting the CFC-11 clearance rates, it is clear that these are massive.”
Between 2014 and 2016, mean emissions were 21% higher than they were between 2002 and 2012. “If the emissions aren’t checked, they could delay the ozone layer healing by about a decade,” Montzka said.
Sarah Iqbal is a senior research fellow at the department of biochemistry, Aligarh Muslim University, India.