Jul 20, 2009

40 Times worse than CO2 methane belched out by megacities

The Los Angeles metropolitan area belches far more methane into its air than scientists had previously realized. If other megacities are equally profligate, urban methane emissions may represent a surprisingly important source of this potent greenhouse gas.

Atmospheric researchers have long had good estimates of global methane emissions, but less is known about exactly where these emissions come from, particularly in urban areas.

To fill this void, a research team led by Paul Wennberg, an atmospheric chemist at Caltech in Pasadena, estimated methane emissions for the Los Angeles region, then subtracted all known sources of methane, such as livestock, landfills and sewage. They ended up with an enormous amount of methane – about 0.14 to 0.34 megatonnes per year, or up to half of the total emissions that could not be accounted for by known sources.

This extra methane may result from higher than expected leakage from landfills, sewage treatment plants or natural gas pipelines, or it could be natural seepage from oil wells or other geologic sources, the researchers say.

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