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.
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!
Ice cave in Transylvania yields window into region's past
28.04.2017 | National Science Foundation
Citizen science campaign to aid disaster response
28.04.2017 | International Institute for Applied Systems Analysis (IIASA)
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
28.04.2017 | Event News
20.04.2017 | Event News
18.04.2017 | Event News
28.04.2017 | Medical Engineering
28.04.2017 | Earth Sciences
28.04.2017 | Life Sciences