Study finds landfill point source emissions have an outsized impact

A new study published in the journal Science reveals the outsized impact of landfill point source emissions, which are responsible for a disproportionately large share of pollution and identifies potential gaps in traditional model-based emission accounting methods.

The study, providing the largest comprehensive assessment of hundreds of U.S. landfills using direct observations through airborne surveys, was led by scientists from Pasadena, California-based nonprofit organization Carbon Mapper alongside researchers from NASA Jet Propulsion Laboratory, Arizona State University, University of Arizona, Scientific Aviation and the U.S. Environmental Protection Agency (EPA).

Emission accounting methods may benefit from sustained direct measurement using emerging surface-, air- and space-based monitoring technologies, the report says.

RELATED: Understanding landfill gas monitoring techniques

“Addressing these high methane sources and mitigating persistent landfill emissions offers a strong potential for climate benefit,” says Dan Cusworth, Carbon Mapper program scientist and lead author on the study. “The ability to precisely identify leaks is an efficient way to make quick progress on methane reduction at landfills, which could be critical for slowing global warming.”

Landfills are considered the third largest source of human-caused methane emissions in the U.S., responsible for 14.3 percent of methane in 2021 and emitting the equivalent to the greenhouse gas emissions from nearly 23.1 million gasoline-powered passenger vehicles driven for one year, according to the EPA. Despite the climate impact of landfills, societal understanding of these emissions is largely limited to model-based estimates, and the sector remains under-addressed compared to other big methane sources like oil and gas.

Traditional surface-based surveys with handheld methane sensors provide an incomplete picture of emissions due to factors including logistical and safety reasons as well as limited access to many sections of active landfills. To help fill these gaps, Carbon Mapper and research partners used advanced aircraft to conduct its survey of active municipal solid waste landfills.

Key findings include:

• High-emissions point sources are more prevalent in landfills vs. oil and gas. Fifty-two percent of surveyed landfills had observable point source emissions.
• Landfill emissions are generally more persistent compared to oil and gas production. Out of the surveyed landfills with observed emissions, 60 percent had emissions that persisted over months or years.
• There is a big difference between observed and reported emissions. On average, aerial emission rates were 1.4 times higher than the EPA’s Greenhouse Gas Reporting Program.

Carbon Mapper’s data can be accessed here.