Levels of an ozone-destroying chemical are mysteriously rising, despite international efforts to crack down on the problem. The uptick in the airborne chemical HCFC-141b comes even though reported production has declined steadily since 2012, leaving scientists stumped about the source. “All I can really say is these emissions are up,” says Luke Western, an atmospheric scientist at the National Oceanic and Atmospheric Administration (NOAA) Global Monitoring Laboratory, who helped lead the new research.

The discovery underscores the challenge of getting rid of these once widely used chemicals, which can linger in appliances for decades. It also shows how continent-size gaps in a network of sensors make it hard to pinpoint sources of the problem.The chemical, used chiefly to make foam insulation for appliances such as refrigerators, is part of a family of fluorocarbon molecules blamed for eating away at a layer of stratospheric ozone, roughly 20 kilometers above the ground, that filters out harmful ultraviolet radiation from the Sun. The world began to wean itself off these chemicals under the 1987 Montreal Protocol, widely considered the most successful international environmental treaty. Overall, ozone-damaging chemicals have declined steadily since the early 2000s, and the ozone “holes” above the poles have begun to heal.

In 2018, however, researchers reported that levels of the banned chemical CFC-11 had been rising since 2012. An international panel concluded that surge was likely due to illicit production, much of it in eastern China, perhaps because HCFC-141b, then used as a substitute for CFC-11 because it is less destructive to ozone, was in scarce supply. Releases of CFC-11 started to fall once again in 2019. By now production of HCFC-141b should also be declining. Its phase-out began in 2013, with a complete ban scheduled for 2030. It is already being replaced by a group of chemicals that doesn’t damage the ozone layer.

But scientists say atmospheric levels of HCFC-141b are actually rising. Emissions have climbed each year between 2017 and 2021, an increase totaling 3000 tons from 2017 to 2020, the researchers estimate. The findings, based on a combination of measurements from air sensors and computer models of how the gases move through the atmosphere, were posted online on 27 April by Atmospheric Chemistry and Physics, although the paper hasn’t been peer reviewed yet. The rise of the newer chemical doesn’t appear to be a repeat of the CFC-11 incident, says Stephen Montzka, an atmospheric scientist who heads NOAA’s monitoring lab and led the work that uncovered the CFC-11 emissions. “I think in the instance of 141b the situation is much murkier,” he says. Results from air sensors in South Korea suggest the problem isn’t originating from eastern China. It does seem to be coming from somewhere in the Northern Hemisphere, because levels have risen faster there than in the south.

One possibility is that unreported HCFC-141b is being manufactured somewhere in the world, Montzka says. But the blip could also be temporary, triggered as aging appliances are thrown out and the foam breaks down, releasing the gas. “Taking a close look, we realized there are possible explanations that don’t require somebody doing something that they weren’t supposed to do,” Montzka says.The monitoring work in papers like this is “critical,” says Helen Walter-Terrinoni, a member of the Montreal Protocol’s technical panel and a chemical engineer with the Air-Conditioning, Heating, and Refrigeration Institute, which represents major manufacturers. The panel reports every 4 years on the state of ozone-depleting gases and the science surrounding them. Its new report, slated for 2023, “could help shed more light on what’s going on” with the rising emissions, Walter-Terrinoni says.

For now, gaps in the air sensor network have made answers elusive. The sensors are concentrated in North America and Europe, with only a handful in East Asia and at isolated sites elsewhere. Scientists are blind to what’s happening in much of India, Russia, and the Middle East, and most of Africa and South America. “If there were emissions in those regions,” Montzka says, “we wouldn’t be able to tell you very accurately where they are coming from.”

The picture could improve in the coming years. In the wake of the CFC-11 incident, an EU-funded initiative is underway to install more sensors and close some of those gaps. For now, Montzka isn’t alarmed about the added dose of chemicals. It amounts to a “small perturbation” in the ozone layer, he says, just a fraction of 1% of the ozone-damaging power of gases now in the atmosphere.

【小题1】Which type of writing does this passage belong to?

A．Descriptive writing.

B．Expository writing.

C．Persuasive writing.

D．Narrative writing.

【小题2】What is the meaning of the underline word ‘illicit’ in Paragraph 3?

A．Valid.

B．Licensed.

C．Constitutional.

D．Illegal.

【小题3】What is the possible reason can explain the fact that atmospheric levels of HCFC-141b are actually rising now?

A．Ground filters out harmful ultraviolet radiation from the Sun.

B．The world began to wean itself off these chemicals.

C．Unreported HCFC-141b is being manufactured somewhere in the world.

D．Ozone-damaging chemicals haven’t declined steadily.

【小题4】Which of the following can be the best title for the text?

A．Atmospheric Levels of HCFC-141b Are Actually Rising

B．Bad Picture Could Improve in The Coming Years

C．Ozone-destroying Chemical Is on The Rise Despite Crackdown

D．Continent-size Gaps in Sensors Make It Hard to Pinpoint Sources of The Problem