The Big Picture of Methane and GHG Emissions: Where Do Landfills Fit in Relative to Other Sources?

Environmental issues continue to play a growing role in national news coverage, whether related to rising sea levels, stronger hurricanes, or greenhouse gas (GHG) emissions. In order to tackle an issue this complex, foundational knowledge is key. How do greenhouse gases affect the atmosphere, and what industries are responsible for the uptick in manmade emissions? The shift to a more sustainable future depends on our commitment to achieving greater understanding through scientific research and data.

The EPA has designated landfills as the third highest source of anthropogenic (manmade) methane emissions in the U.S., behind the oil and agriculture industries. Methane is a leading contributor to climate change and is responsible for roughly one-fifth of the enhanced greenhouse effect. According to recent data, the United States produces 347 million tons of trash annually – over six pounds per person, per day. If not recycled or composted, 64% of that trash gets dumped into one of the 1,475 landfills across the United States.

As organic materials break down, landfills naturally produce methane, but what role does that process play in overall greenhouse gas emissions? Methane emissions represent roughly 11% of total GHG emissions in the U.S.  The top three industries emitting methane are: agriculture via enteric fermentation (i.e. livestock), natural gas systems (e.g. distribution, storage for heat/energy), and landfills. According to the EPA, in 2020, these 3 industries represented 27%, 25%, and 17% of total methane emissions, respectively.

While methane emissions from agriculture and natural gas systems are collectively much higher, landfills are still a significant source of methane emissions.  Thus, it’s important to know how and why landfills emit methane, and further, how to measure these emissions, in order to effectively mitigate and reduce them. Anaerobic biological processes (when organic matter breaks down in the absence of oxygen) are what cause methane and carbon dioxide emissions in landfills. Landfill gas is typically collected, and the methane is either burned off, which reduces its global warming potential, or is used to create energy, which can provide a net benefit as this offsets fossil-based energy. However, a fraction of this methane escapes capture and is referred to as “fugitive emissions.”

Scientific advances in the ability to measure large-area sources of methane emissions at lower levels are bringing into focus, for the first time, the potential to accurately measure landfills’ methane emissions economically and over much faster time scales compared to a decade ago. While more landfill-specific data is needed to establish variability, particularly over larger, annual time frames, the same methods used for landfills may potentially be utilized in the agriculture industry for measuring livestock waste lagoons and feedlots.

To build this needed data, EREF issued a grant to Florida State University that aims to aggregate data from direct landfill emissions measurements taken at landfills across the U.S.. Dr. Tarek Abichou, PhD, PE, FAMU-FSU College of Engineering, is the principal investigator on the project, which will combine data from a variety of direct emission measurement technologies, with some sites being measured for emissions using multiple technologies over the same time frames to allow intercomparison of results. If successful, the project will allow for the effectiveness of different methods to be compared while also inching closer to using whole site measurements to estimate annual emissions.

The quantification of landfill emissions has improved significantly over the past 2 decades. Direct measurement technology, in particular, has seen significant progress and technology advances over a short period of time which are analogous to moving from the horse and buggy to automobiles. Such significant strides forward offer opportunities since the accuracy of these direct measurement technologies are viewed as more accurate than model-based estimates, which have been used for decades. The primary challenge at this point is ensuring accountability in the use of the methods, since ease of measurement doesn’t necessarily imply higher accuracy. In this respect, the project described above provides benchmarking to better understand how consistent these methods can be under different conditions, such as heavy winds or overcast skies. Collectively, the use of direct methods and ensuring a clear understanding of their accuracy and limitations provide transparency and higher certainty in the impact that methane emissions from landfills have on overall GHG emissions, which is an element that landfill owners, policymakers, and environmental groups all desire.