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 NASA examines Peru's deadly rainfall
24.03.2017 | NASA/Goddard Space Flight Center

nachricht Steep rise of the Bernese Alps
24.03.2017 | Universität Bern

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Argon is not the 'dope' for metallic hydrogen

24.03.2017 | Materials Sciences

Astronomers find unexpected, dust-obscured star formation in distant galaxy

24.03.2017 | Physics and Astronomy

Gravitational wave kicks monster black hole out of galactic core

24.03.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>