Abstract
Methane is one of the most important gaseous hydrocarbon species for both industrial and environmental reasons. Understanding and quantifying methane emissions to atmosphere is therefore an important element of climate change research. Range-resolved infrared differential absorption Lidar (DIAL) measurements provide the means to map and quantify a wide range of different methane sources. This paper describes the DIAL measurement technique and reports the application of an infrared DIAL system to field measurements of methane emissions from active and closed landfill sites. This paper shows how the capability of the DIAL to measure the spatial distribution of methane plumes enables DIAL vertical scans to spatially separate and independently quantify emissions from different sources. It also allows DIAL horizontal scans carried out above the surface to identify emission hot-spots. An overview of the landfill emission surveys carried out over the last decade by the National Physical Laboratory (NPL) DIAL system is presented. These surveys were part of research projects and commercial works aimed to validate the method and to provide reliable information on the methane emissions measuring the total site and area-specific emissions from active areas, capped areas, and gas engine stacks. This work showed that methane emissions are significantly higher for active sites than closed sites due to the methane emitted directly to air from the uncapped active areas. On active sites, the operational tipping areas generally have higher emission levels than the capped areas, although there is considerably variation in the emission from different capped areas. The information obtained with DIAL measurements allow site operators to identify significant fugitive emission sources and validate emissions estimates, and they allow the regulators to revise and update the emission inventories. Operators’ remediation actions driven by DIAL measurements have also been shown to considerably decreased total site methane emission.
Highlights
Landfills constitute one of the major anthropogenic sources of methane in many developed countries
The Intergovernmental Panel on Climate Change (IPCC) guidelines indicate that measurement of methane emissions is necessary to validate emission models and to provide confidence in country specific model parameters which will provide the basis for further mitigation measures if required
A further aim was to quantify the emission from the gas engines so that this could be compared to the predicted methane emissions
Summary
Landfills constitute one of the major anthropogenic sources of methane in many developed countries. The reported emissions from landfills for emission inventories are commonly estimated by using internationally agreed computer models such as GasSimTM [2]. This approach often involves large uncertainties due to inaccuracies of the input data and many assumptions in the estimation [3]. The IPCC guidelines indicate that measurement of methane emissions is necessary to validate emission models and to provide confidence in country specific model parameters which will provide the basis for further mitigation measures if required.
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