Methane Hotspots in the Los Angeles Megacity
Abstract
Airborne observations show that Los Angeles (LA) is a large source of methane to the atmosphere, yet the sources of excess methane from the urban area are poorly constrained. We used a mobile laboratory, a Ford Transit van equipped with cavity ring down spectrometers (Picarro, Inc.), to measure greenhouse gases (CH4, CO2, and CO) mole fractions in LA. On-road surveys across the LA Basin were conducted seasonally to determine patterns of CH4 enrichment in space and over time, with a focus on quantifying methane leaks from known sources. We found fugitive leaks and elevated CH4 concentrations throughout the LA Basin. Some were associated with known sources, such as landfills, wastewater treatment, and oil and gas infrastructure, while others had an unknown origin. Urban CH4 enrichment varied over the course of the year, largely due to seasonal changes in meteorological conditions. Nevertheless, our mobile surveys revealed CH4 hotspots (>200 ppb elevated with respect to background levels) that persisted among seasons. High CH4 concentrations were most easily predicted by proximity to methane sources, particularly near the coast, while elevated CH4 levels were more evenly dispersed in inland areas. CH4 hotspots had a disproportionate impact on excess methane relative to the area they accounted for, typically providing more than a quarter of excess methane measured on a transect. These data improve estimates of the relative roles of specific leaks and emission sectors to LA's excess methane. Depending on the cost of reducing these CH4 leaks, a focus on CH4 emissions may prove an effective way to reduce LA's greenhouse gas emissions in the near term.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.A53E0221H
- Keywords:
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- 0345 ATMOSPHERIC COMPOSITION AND STRUCTURE Pollution: urban and regional;
- 0493 BIOGEOSCIENCES Urban systems;
- 0490 BIOGEOSCIENCES Trace gases;
- 1610 GLOBAL CHANGE Atmosphere