Methane Across the Country
Methane is created naturally near the Earth's surface, primarily by microorganisms by the process of methanogenesis. It is carried into the stratosphere by rising air in the tropics. Methane is a potent greenhouse gas, stronger than carbon dioxide on a 20-year timescale, according to the Intergovernmental Panel on Climate Change, though on a century timescale, carbon dioxide is far stronger. "This research suggests significant benefits to slowing climate change could result from reducing industrial methane emissions in parallel with efforts on carbon dioxide," said Ira Leifer, a researcher with UC Santa Barbara's Marine Science Institute. Doing a a cross-continent drive, a UC Santa Barbara scientist has found that methane emissions across large parts of the U.S. are higher than is currently known, confirming what other more local studies have found. Their research is published in the journal Atmospheric Environment.
Leifer was joined by two UC Santa Barbara undergraduate students on the road trip from Los Angeles to Florida, taking a primarily southern route through Arizona, New Mexico, Texas, Louisiana, and along the Gulf of Mexico. They used specialized instrumentation, a gas chromatograph, to measure methane. The device was mounted in the RV, with an air ram on the roof that collected air samples from in front of the vehicle.
"We tried to pass through urban areas during nighttime hours, to avoid being stuck in traffic and sampling mostly exhaust fumes," Leifer said. "Someone was always monitoring the chromatograph, and when we would see a strong signal, we would look to see what potential sources were in the area, and modify the survey to investigate and, if possible, circumnavigate potential sources."
The researchers meandered slowly through areas of fossil fuel activity, such as petroleum and natural gas production, refining, and distribution areas, and other areas of interest. The wide range of sources studied included a coal-loading terminal, a wildfire, and wetlands.
The sources of methane can be natural, industrial, natural gas (which is mostly methane), and residential such as home heating.
Methanogenesis or biomethanation is the formation of methane by microbes known as methanogens. Organisms capable of producing methane have been identified only from the domain Archaea, a group phylogenetically distinct from both eukaryotes and bacteria, although many live in close association with anaerobic bacteria. The production of methane is an important and widespread form of microbial metabolism. In most environments, it is the final step in the decomposition of biomass.
All combustion processes, whether they are cars, boilers, or engines that burn fuel will release a little methane from incomplete combustion.
The team analyzed the data in conjunction with researchers at the University of Bremen, Germany, who analyzed inventories and satellite data from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instrument onboard the European Space Agency's (ESA) ENVISAT satellite to confirm the finding of strong methane sources in regions of fossil fuel activity. The surface measurements found methane levels increased as the researchers moved toward Houston, and then decreased as they continued westward — the same trend observed in satellite data spanning the continent.
Previous methane studies have focused primarily on large-scale airborne data, which were hard to separate from localized sources, according to Leifer. In fact, clear identification of individual sources often could not be conducted, requiring computer models and other surface measurements.
The team compared maps of estimated methane emissions based on data from the International Energy Agency of the U.S. Department of Energy with satellite methane maps. They found that, in some cases, to explain observed higher methane concentrations required higher emissions than current emission maps present, particularly in large regions of fossil fuel industrial activity. In other cases, though, they could rule out that wetlands such as swamps may have been important. In such cases, separating wetland methane contributions from fossil fuel industrial contributions was not possible with their approach, Leifer said, "This is a topic we are investigating further through new research," he added.
"Methane is the strongest human greenhouse gas on a political or short timescale, and also has more bang for the buck in terms of addressing climate change," said Leifer. "This research supports other recent findings suggesting that fugitive emissions from fossil fuel industrial activity actually are the largest methane source. This clearly indicates a need for efforts to focus on reducing these methane emissions."
The researchers found the highest methane concentrations in areas with significant refinery activity, and in California in a Central Valley region of oil and gas production. Methane levels near refineries were not uniform, varying greatly from spot to spot and at different times. Nighttime concentrations were dramatically enhanced when the winds died down, forming a calm, shallow atmospheric layer near the surface, according to Leifer.
Perhaps the most surprising discovery was made in the Los Angeles area, where the study highlighted the importance of geologic methane emissions in the North Los Angeles Basin, centered on the La Brea Tar Pits. Rough estimation of emissions from the data suggests 10-20 percent of the methane emissions from Los Angeles could be natural geologic, influenced by the vast number of abandoned wells throughout the area.
For further information see Methane.
Atmosphere image via Wikipedia.