- Milton, M J T, Goody, B A, Partridge, R H, Andrews, A
- NPL Report QM 134, June 1997
- NPL Doc. Ref:
- PDB: 1277
- Document Type:
- NPL Report
Note: An asterisk after an author's name indicates a non-NPL author.
Methane is the second most important of the greenhouse gases (after carbon dioxide), and contributes approximately 12% of the global warming potential of all man-made gases emitted by the UK at present. The anaerobic decay of organic waste in landfill sites is a major national source of methane, but a lack of detailed information on emissions has resulted in large uncertainties in current estimates. In .view of the importance of methane emissions from landfill to total UK greenhouse gas emissions, this study was commissioned to establish an improved estimate based on direct flux measurements.Measurements of the flux of methane have been carried out at 35 representative sites using three complementary techniques: optical integrated-path, flux survey and flux enclosure methods. The sites were chosen to be representative of UK conditions, and included, inter alia, large modem sites incorporating the latest gas-control systems, older sites that have had gas-control systems fitted after completion and sites that have not received waste or maintenance for more than 15 years.The results show that the principal factors that influence the total emissions of methane to atmosphere from a landfill site are: the depth of waste in place and the presence of a comprehensive gas extraction system (together with a low permeability capping layer). A statistical stratification of the flux measurements was used to divide the sites into four categories. The mean for each category was then scaled to calculate total annual emissions from the UK using information about the number and size ofsites in each category.Total methane emissions from landfill are estimated to have been 887 kt y-l in 1995, with a 90% confidence interval between 652 kt y-l and 1135 kt y-l. The measurements have demonstrated that fluxes of methane from landfill sites that have comprehensive gas extraction systems (and low permeability caps) are significantly lower than estimated in previous studies which relied solely on model calculations.Taking into account known and anticipated changes in the mass of waste being sent to each category of landfill, annual UK emissions of methane from landfill are estimated to have been 1039 kt y-l in 1990, and are estimated to fall to 699 kt y-l by 2000 and 349 kt y-l by 2010.
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