A Field-Verified Model to Estimate Landfill Methane Flux Using Surface Methane Concentration Measurements under Calm Wind Conditions

Abstract

A significant portion of anthropogenic greenhouse gas emissions––that are suspected of contributing to global warming––are emitted from landfills accepting biodegradable organic waste. Thus, the assessment of fugitive methane emissions from landfill surfaces has become an important and integral part of determining the overall carbon budgets of individual countries. Quantifying fugitive methane emissions from landfills using indirect methods, such as predictive mathematical models, which has been the norm for a long time, have proven to be ineffective for current needs. In recent years, attention has shifted to direct measurements, such as the flux chamber method, which is also costly and labor intensive, considering the vast areas covered by landfill surfaces. However, collecting surface methane concentration (SMC) data through an instantaneous emission measurement technique is relatively simple and inexpensive. Although the SMC is only a qualitative indicator of the methane flux of a landfill, recent literature on this topic has pointed to a potentially strong correlation between SMCs and methane flux. In this context, establishing a simple but robust model, capable of estimating methane surface flux using SMC values, was the primary aim of the research described here. In this study, we investigated the correlation between SMCs and methane flux across the soil–atmosphere boundary in a small-scale test cell under a partially controlled environment. The data collected from the test cell were used to propose a linear regression model that suggested that the methane flux under calm wind conditions could be simply predicted as 1.264 times the SMC. This model was then verified in a field lysimeter, which consisted of material similar to what is found in a landfill biocover. The model was able to predict the methane flux at the field lysimeter with an absolute average error of 40%. This error margin is quite reasonable because, as per the literature, error margins as high as 190% are not uncommon in estimating the methane flux at landfills using other commonly adopted methods.