Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

When less is more

01.03.2016

NOAA, CIRES study tracks down lingering source of carbon tetrachloride emissions

Carbon tetrachloride (CCl4) was once commonly used as a cleaning agent and remains an important compound in chemical industry. CCl4 is responsible for that sickly sweet smell associated with dry cleaning solvents from decades ago.


A graphic of the Earth's ozone layer.

Credit: NASA

It's a known air toxin and it eats away at the ozone layer--the gas accounts for about 10-15 percent of the ozone-depleting chemicals in the atmosphere today. As a result, production across the globe has been banned for many years for uses that result in CCl4 escaping to the atmosphere.

Given these stringent limits, the chemical is being released into the air at small rates here in the United States, but a new study reports those rates are still 30 to 100 times higher than amounts reported to emission inventories.That study, led by CIRES scientist Lei Hu and NOAA scientist Stephen Montzka, also suggests that the source of the unexpected emissions in the U.S. appears associated with the production of chlorinated chemicals (such as those ultimately used to create things like Teflon and PVC). The new analysis is published today in the Proceedings of the National Academy of Sciences.

In the 1980s, when scientists discovered that CCl4 was contributing to the destruction of the ozone layer, the synthetic compound was included on a list of substances to be phased out of production. That list, part of the Montreal Protocol on Substances that Deplete the Ozone Layer, required that production for dispersive use (uses that would result in escape to the atmosphere) of CCl4 be discontinued in developed countries by 1996, and in developing countries by 2010.

Despite that phase out, the decline of CCl4 in the atmosphere has been unexpectedly slow. That left many scientists puzzled, including Montzka, who works in NOAA's Earth System Research Laboratory (ESRL) and is also a CIRES Fellow. "We've been scratching our heads, trying to understand why," he said. "When we look at the amounts produced and destroyed, which industry throughout the world has reported to the Ozone Secretariat, we would expect the chemical's global concentration to be decreasing at a rate of nearly 4 percent per year. But it's only decreasing at 1 percent per year. So what's happening?"

To investigate the U.S. contribution, Montzka, Hu and colleagues from NOAA, CIRES, and other scientific institutions studied observations made from NOAA's North American air sampling network. Since the late 2000s, they tracked the composition of the atmosphere from this network of nine tall towers and many more regular aircraft-sampling sites across North America. "We wanted to identify where these emissions were coming from, as well as their magnitude," Hu said.

She and her colleagues considered landfills, where residual amounts of CCl4 might still be leaking from old fire extinguishers or solvent cans, given that CCl4 was used for these purposes in the early to mid-1900s. The team looked at high-density population areas to determine if the use of bleach or chemicals in laundry or swimming pools might be responsible for the emissions they detected. They also checked into industrial sources--and here they had some help.

The Environmental Protection Agency requires industries to report CCl4 emissions. Hu and Montzka were able to compare that information against what they derived from their precise atmospheric measurements of CCl4 concentrations across the country. The analysis of all those data suggests that the CCl4 emissions arise from the same geographic areas as those industries reporting to the EPA. Not a huge surprise, but the amount found was 30 to 100 times higher than what was being reported. The most significant hot spot was the Gulf Coast region, with smaller emissions in Colorado and California.

"We can't tell exactly what the sources of emissions are," said Montzka. "It could be underreporting from known sources, it could be an unknown source, it could be both. It could be some other activity that's geographically tied to the production of chlorinated chemicals and products that hasn't been recognized previously as a significant source."

Hu and Montzka said they hope their work inspires more research, both here in the United States and internationally, to better pin down the precise reasons for excess emissions. The researchers reported in the new paper that the United States has been responsible for about 8 percent of the overall global CCl4 emissions in recent years. If the processes that emit CCl4 in the U.S. also happen in other places, it would go a long way towards explaining the slow rate of decline of CCl4 in the global atmosphere.

"Before this work," said Montzka, "There'd been very little progress on understanding the mystery of continuing global emissions of CCl4. Now we have a better picture, at least in the United States, of where some of those emissions are coming from. That's the first step towards minimizing emissions in the future and speeding up the recovery of the ozone layer."

###

Authors of "Continued emissions of carbon tetrachloride from the U.S. nearly two decades after its phase-out for dispersive uses" are L. Hu (CIRES and NOAA), S. A. Montzka (NOAA), B. R. Miller (CIRES and NOAA), A. E. Andrews (NOAA), J. B. Miller (NOAA) S. J. Lehman (INSTAAR, CU-Boulder), C. Sweeney (CIRES and NOAA), S. Miller (Stanford University), K. Thoning (NOAA), C. Siso (CIRES and NOAA), E. Atlas (University of Miami), D. Blake (University of California Irvine), J. A. de Gouw (CIRES and NOAA), J. B. Gilman (CIRES and NOAA), G. Dutton (NOAA), J. W. Elkins (NOAA), B. D. Hall (NOAA), H. Chen (University of Groningen, the Netherlands), M. L. Fischer (Lawrence Berkeley National Laboratory), M. Mountain (Atmospheric and Environmental Research), T. Nehrkorn (Atmospheric and Environmental Research), S. C. Biraud (Lawrence Berkeley National Laboratory), F. Moore (CIRES and NOAA) and P. P. Tans (NOAA)

CIRES is a partnership of NOAA and CU-Boulder.

Laura Krantz | EurekAlert!

Further reports about: Atmosphere CCl4 CIRES EMISSIONS Environmental Research NOAA ozone ozone layer

More articles from Earth Sciences:

nachricht Predicting unpredictability: Information theory offers new way to read ice cores
07.12.2016 | Santa Fe Institute

nachricht Sea ice hit record lows in November
07.12.2016 | University of Colorado at Boulder

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Electron highway inside crystal

Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.

Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

Researchers identify potentially druggable mutant p53 proteins that promote cancer growth

09.12.2016 | Life Sciences

Scientists produce a new roadmap for guiding development & conservation in the Amazon

09.12.2016 | Ecology, The Environment and Conservation

Satellites, airport visibility readings shed light on troops' exposure to air pollution

09.12.2016 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>