Field measurement of landfill methane emissions and laboratoryfield measurements of methane oxidation

Unlike for CH4 emissions and oxidation in wetlands, soils and rice production systems during the last two decades, there have not been comprehensive regional field campaigns addressing landfill CH4 emissions. In large part, because landfills are discrete sites dispersed across the landscape, field campaigns to date have focused on specific sites and have rarely included multiple seasons or years. Previous summaries, mostly for small-scale (chamber) measurements, have reported positive emission rates ranging over seven orders of magnitude from 0.0004g CH4 m-2 d-1 to more than >4000g CH4 m-2 d-1 (Bogner et al, 1997b, and references cited therein); Scheutz et al (2009) reported maximum rates of 1755g CH4 m-2 d-1. Landfill field studies to date have also reported negative fluxes (uptake of atmospheric CH4) at rates ranging over six orders of magnitude from -0.000025 to -16g m-2 d-1 (Bogner et al, 1997b, Scheutz et al, 2009 and references cited therein). Techniques that have been used for field measurement of landfill CH4 emissions include: (1) surface techniques (static and dynamic chambers); (2) above-ground micro-meteorological (eddy correlation, mass balance), remote sensing (lidar, tunable diode laser (TDL), and static/dynamic tracer techniques; and (3) below-ground gradient techniques (concentration profiles). The advantages and disadvantages of the various techniques for landfill applications have been previously summarized in Bogner et al (1997b), Scheutz et al (2009) and references cited therein. In general, it is important to consider site-specific constraints with respect to application of specific techniques, including variable emission signals from adjacent cells with different cover materials (daily, intermediate, final), complex topography, variable slopes and localized meteorology. Often the use of two or more techniques in combination is recommended, such as the use of an above-ground technique (for whole-cell emissions) with static chambers (to characterize the variability of emissions across a cell).

Typically, published data to date indicate that rates at individual sites can vary spatially over two to four orders of magnitude over short distances (m).

Both 'hot spots' with elevated emissions and points of negative emissions are common at landfills over small spatial scales (Figure 11.1); thus, geostatistical methods must be applied to small-scale chamber results to determine whole-landfill fluxes (for example Graff et al, 2002; Spokas et al, 2003; Abichou et al, 2006a). Often the landfill surface emissions are characterized by minimal to no spatial structure as indicated through semi-variogram models (Graff et al, 2002; Spokas et al, 2003). In most cases, inverse distance weighting (IDW) is the recommended interpolation method for deriving area emissions from chamber results due to the lack of spatial structure that is a prerequisite for other kriging methods (Abichou et al, 2006a; Spokas et al, 2003). However, a large number of individual chamber measurements are required to adequately

Negative Flu* (Uptake)

■1

0 - 0.5 g irr d 1 CHJ

Ml

0.5 -10 g m"£ d 1 CH4

HI

10 -100 g m? d 1 CHj

IS!

100 - 200 g m"£ ¿"'CH,

B

Z00-500g m"Jd ' CHa

>500 g mJ d ' CH,

0 0

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