Methodologies for measuring fugitive methane emissions from landfills - A review

Abstract

Fugitive methane (CH₄) emissions from landfills are significant global sources of greenhouse gases emitted into the atmosphere; thus, reducing them would be a beneficial way of overall greenhouse gas emissions mitigation. In Europe, landfill owners have to report their annual CH₄ emissions, so direct measurements are therefore important for (1) evaluating and improving currently applied CH₄ emission models, (2) reporting annual CH₄ emissions and (3) quantifying CH₄ mitigation initiatives. This paper aims at providing an overview of currently available methodologies used to measure fugitive CH₄ emissions escaping from landfills. The measurement methodologies are described briefly, and the advantages and limitations of the different techniques are discussed with reference to published literature on the subject. Examples are given of individual published studies using different methodologies and studies comparing three or more methodologies. This review suggests that accurate, whole-site CH₄ emission quantifications are best done using methods measuring downwind of the landfill, such as tracer gas dispersion and differential absorption LiDAR (DIAL). Combining aerial CH₄ concentration measurements from aircraft or unmanned aerial vehicles with wind field measurements offers a great future potential for improved and cost-efficient integrated landfill CH₄ emission quantification. However, these methods are difficult to apply for longer time periods, so in order to measure temporal CH₄ emission changes, e.g. due to the effect of changes in atmospheric conditions (pressure, wind and precipitation), a measurement method that is able to measure continuously is required. Such a method could be eddy covariance or static mass balance, although these procedures are challenged by topography and inhomogeneous spatial emission patterns, and as such they can underestimate emissions significantly. Surface flux chambers have been used widely, but they are likely to underestimate emission rates, due to the heterogeneous nature of most landfill covers resulting in sporadic and localised CH₄ emission hotspots being the dominant emission routes. Furthermore, emissions from wells, vents, etc. are not captured by surface flux chambers. The significance of any underestimation depends highly on the configuration of individual landfills, their size and emission patterns.

Keywords: DIAL; Eddy covariance; Landfill gas; Mass balance; Qualitative methane reconnaissance techniques; Radial plume mapping; Surface flux chambers; Tracer gas dispersion.