Mystery methane belched out by megacities

The Los Angeles metropolitan area belches far more methane into its air than scientists had previously realised. 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.’

“There’s a sizeable amount of emissions that seem not to be catalogued right now,” says Wennberg. “You’d like to find out what’s the source, so you can put a stopper in it.”

New Scientist