Extra-frigid temperatures in Antarctica this year produced an ozone hole nearly 3 million square kilometres larger than what scientists have measured in the past couple of years, US government researchers said on 2 November.
Colder temperatures encourage the formation of ice crystals high in the atmosphere over the Antarctic. The ice grabs onto chemicals that contain chlorine, such as those derived from chlorofluorocarbons (CFCs), and breaks them apart — producing chlorine atoms that eat away at the ozone layer. This process resulted in a nearly 23-million-square-kilometre hole this year.
Diminishing levels of ozone-depleting chemicals in the atmosphere kept the hole much smaller this year than it could have been, NASA and the National Oceanic and Atmospheric Administration (NOAA) said.
But revelations earlier this year of rogue emissions of ozone-destroying chemicals, including CFCs, have raised alarms among scientists and policymakers. The 1987 Montreal Protocol banned the manufacture and use of such chemicals to protect the ozone layer, which filters out harmful radiation. Researchers fear that the rogue emissions, which persist in the atmosphere for about 50 years, could set back the ozone layer’s recovery by a decade or more. Their challenge now is to uncover the source of these chemicals.
Hunting for sources
Studies published in May,1 August2 and September3 identified a slower-than-expected disappearance of ozone-depleting chlorine gases in the atmosphere, including trichlorofluoromethane (CFC-11) and its parent molecule, carbon tetrachloride.
Before the Montreal Protocol phased out their use and manufacture, ozone-depleting chemicals were used to produce coolants in refrigerators, cleaning solvents and certain types of insulating foams.
Because scientists know how long CFC-11 and carbon tetrachloride persist in the atmosphere, they can calculate how much should be left based on historic emissions data. Based on those estimates, the authors of the the study published in May surmised that the slower decline in CFC-11 and carbon tetrachloride levels was the result of fresh emissions.
Separate investigations earlier this year by The New York Times and the Environmental Investigation Agency, an advocacy organization in Washington DC, identified at least 18 Chinese factories still making or using CFC-11. The Chinese government is conducting its own investigation.
It can take decades for ozone-depleting chemicals such as CFCs to make it high enough into the atmosphere to start causing problems.
“So, the emissions that we’ve seen — these increases of CFC-11 emissions — probably had almost no impact on the ozone hole this year,” says Paul Newman, chief scientist for Earth sciences at NASA Goddard Space Flight Center.
The Montreal Protocol’s Technology and Economic Assessment Panel will likely include a reassessment of how much CFC-11 is leaking from materials such as discarded refrigerators, says Stephen Andersen, American director of research at the Institute for Governance and Sustainable Development, an environmental group in Washington DC. The Montreal Protocol group issues a report every four years on technologies that could aid in eliminating ozone-depleting chemicals.
Scientists — including Stephen Montzka, a research chemist for NOAA in Boulder, Colorado, and the lead author on the study published in May — are reviewing CFC-11 measurements taken in Japan, South Korea and China to see whether they can trace the source of the extra emissions.
They’re also trying to get CFC-11 measurements from sites closer to alleged sources in East Asia. With that information, researchers will be able to “pinpoint, basically, where the emissions are coming from”, Montzka says.
But the manufacture and use of CFC-11 might not be the only reason for the slower rate at which the chemical is vanishing from the atmosphere, says Andersen. Researchers could be wrong about the lifespan of CFC-11, he says. Or, the CFC-11 emissions could be leaking from old foam insulation and refrigerants.
“It’s really mysterious,” Andersen says. “We know that some portion of this total mystery is China. We just don’t know how much so far.”