Research and analysis

Using inverse dispersion modelling to quantify methane emissions from landfills: summary

Published 7 August 2026

Applies to England

1. Waste and Resources research report summary

This project continued the Environment Agency’s investigation into how a technique known as inverse dispersion modelling could be used to estimate the amount of methane released from landfill sites.

1.1 Background 

Methane is an important greenhouse gas which is much more potent than carbon dioxide. Methane is one of the main gases that are produced in landfills as organic waste decomposes, and landfills are a major source of anthropogenic methane emissions. It is therefore important that releases of methane from landfill sites are effectively managed to reduce climate impacts. Methane emission rates from individual sites are poorly understood, and Defra and the Environment Agency are working on methods to quantify emissions, including the Tracer Dispersion Method (TDM). However, no single approach is suitable for all landfills or survey conditions, and a flexible toolkit of complementary methods is needed.

Inverse dispersion modelling (IDM) reverses the conventional dispersion modelling approach: rather than predicting downwind concentrations from known or assumed emissions, it infers emissions from measured downwind concentrations. Earlier work on quantifying methane emissions using inverse dispersion modelling  demonstrated IDM’s potential for landfill methane emission quantification. Building on that work, this project aimed to develop an auditable IDM protocol that could estimate landfill methane emission rates using concentration measurements across the downwind methane plume (a measurement transect).

1.2 Approach 

This study used an IDM approach which had been recommended for exploration in the earlier work. This involves applying an IDM method to the gas concentration integrated across the whole downwind plume. This approach compares the measured and modelled crosswind integrated concentrations which means that the sensitivity to short term turbulence and wind meander is minimised.

The project used datasets of downwind methane and tracer concentrations from TDM surveys conducted for the Environment Agency and Defra. The datasets, where tracer release rates and TDM-derived methane emissions were known, were analysed to refine the IDM calculation approach and evaluate the model performance using both methane and tracer emissions. Potential factors influencing uncertainty were quantified, including wind speed, wind direction, orientation of the transect with respect to wind direction, and the distribution of emissions across the landfill.

1.3 Results and outputs

The project developed a practical IDM protocol which uses downwind methane concentration measurements across the plume, meteorological data, and a suitable dispersion model. It avoids the need for site access and does not require the tracer component of TDM surveys. The protocol specifies detailed requirements for downwind transect suitability, survey planning considerations, uncertainty quantification procedures, and provides a reporting template.

The protocol was tested using TDM data and, applying the protocol’s transect selection criteria, resulted in improved agreement with TDM methane emission rates compared with earlier results using a broader set of transects. The protocol was also blind tested using new survey data; only after results were submitted were the corresponding TDM emission rate values revealed. IDM and TDM methane emissions rates agreed well with an average IDM:TDM ratio of 0.91 (an exact match would give a ratio of 1).

Uncertainty analysis showed that wind speed uncertainties are important, with sensitivity of the estimated methane emission rate to wind speed uncertainty decreasing as wind speed increased. Therefore, the protocol requires a minimum wind speed of 3 metres per second. Plume identification and the subtraction of the ambient background methane concentration were also a source of uncertainty. The largest contributor to the overall uncertainty on the methane emission rate was variability between the transects in a survey. So, the protocol requires the reporting of the mean and standard deviation across all modelled transects.

1.4 Conclusion

The IDM protocol performed well in matching the calculated TDM methane emission rates. This suggests that IDM can be a potential option for quantifying methane emissions from landfills.

Although the IDM protocol has been robustly tested, IDM could be applied to landfill sites surveyed specifically under the protocol’s requirements to investigate the potential for reducing the recommended number of transects. Further work on uncertainty could include surface roughness, meteorological inputs from Numerical Weather Prediction models, and statistical methods for plume identification and background estimation. The protocol could also be tested more broadly for different methane sources and for other pollutants to determine the applicability of IDM to other facility types.

1.5 Publication details

This summary relates to information from project RDE 814, reported in detail in the following output:

• Report: RDE 814
• Title: Using inverse dispersion modelling to quantify methane emissions from landfills
• Technical Lead: Mark Bourn, Chief Scientist’s Group
• Research Contractor: Cambridge Environmental Research Consultants (CERC) under contract to: Air Quality Consultants (AQC)

This project was commissioned by the Environment Agency’s Environment and Business Directorate.

Enquiries: research@environment-agency.gov.uk.

© Environment Agency