Research and analysis

Investigating variability in landfill methane emissions using air quality monitoring data: summary

Published 5 September 2024

Applies to England

1. Chief Scientist’s Group report summary

This project took an existing set of measurements of methane concentrations around a landfill and used these data in computer models to estimate methane emission rates and see how these change over time. Methane is a greenhouse gas with an ability to trap heat in the atmosphere greater than that of carbon dioxide. Methane emissions from landfills are poorly understood and a better understanding of how landfill methane emissions vary could inform both improvements to the reporting of methane emissions and possible regulatory approaches.

1.1 Approach

The work was undertaken in four stages:

1. Estimating methane emission rates based on what was happening at the landfill (for example capping of the landfill surface);
2. Using those emission estimates in dispersion models to simulate ambient methane concentrations;
3. Undertaking inverse modelling to infer methane emission rates that minimise differences between the modelled and measured methane concentrations;
4. Analysing the resulting methane emission rate estimates to identify possible reasons for variations.

1.2 Results

The monitoring data used in the project was not specifically designed for inverse modelling and so posed significant challenges, contributing to high uncertainties in the estimated emissions.

The results show large changes in estimated methane emission rates over the study period. The results suggest that meteorological factors are not a dominant factor in the variability of methane emission rates. While wind speed and barometric pressure may have some effect on landfill methane emissions rates, that effect is relatively small. A more important factor in variability is operational activity at the landfill site, with the largest single factor being the landfill surface status, with some variability explained by the rate of landfill gas collection. Capping and gas collection work together as part of the overall landfill gas management system so while the surface status appears to be the biggest driver in variability, it would not be as effective without the gas extraction system.

1.3 Conclusions

The study period involved a lot of operational changes at the landfill, and the uncertainties in the emission rates are high, so caution is needed in drawing strong conclusions on the applicability of the findings to other landfills.

The analysis does suggest that estimating total annual methane emissions for a landfill from a single survey would be challenging as emission rates can be highly variable. However, the findings suggest that, for periods of relatively stable site operations, a single methane emission survey could reflect the standard of landfill gas management performance in that period. The results also suggest that an operational landfill can capture a high proportion of the generated methane in the landfill gas management system.

1.4 Publication details

This summary relates to information from project SC220016, reported in detail in the following output:

• Report: SC220016/R
• Title: Investigating variability in landfill methane emissions using air quality monitoring data *Project manager: Mark Bourn, Climate Change and Resource Efficiency
• Research contractors: Air Quality Consultants (AQC) and Cambridge Environmental Research Consultants (CERC)

This project was commissioned by the Environment Agency’s Chief Scientist’s Group, which provides scientific knowledge, tools and techniques to enable us to protect and manage the environment as effectively as possible.

Enquiries: [email protected].

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