CH<sub>4</sub> emission estimates from an active landfill site inferred from a combined approach of CFD modelling and in situ FTIR measurements

Abstract

Abstract. Globally, the waste sector contributes to nearly a fifth of anthropogenic methane emitted to the atmosphere and is the second largest source of methane in the UK. In recent years great improvements to reduce those emissions have been achieved by the installation of methane recovery systems at landfill sites, and subsequently methane emissions reported in national emission inventories have been reduced. Nevertheless, methane emissions of landfills remain uncertain and quantification of emission fluxes is essential to verify reported emission inventories and to monitor changes in emissions. Here we present a new approach for methane emission quantification from a complex source such as a landfill site by applying a computational fluid dynamics (CFD) model to calibrated in situ measurements of methane as part of a field campaign at a landfill site near Ipswich, UK, in August 2014. The methane distribution for different meteorological scenarios is calculated with the CFD model and compared to methane mole fractions measured by an in situ Fourier-transform infrared (FTIR) spectrometer downwind of the prevailing wind direction. Assuming emissions only from the active site, a mean daytime flux of 0.83 mg m −2 s −1 , corresponding to a spatially integrated emission of 53.3 kg h −1 , was estimated. The addition of a secondary source area adjacent to the active site, where some methane hotspots were observed, improved the agreement between the simulated and measured methane distribution. As a result, the flux from the active site was reduced slightly to 0.71 mg m −2 s −1 (45.6 kg h −1 ), and at the same time an additional flux of 0.32 mg m −2 s −1 (30.4 kg h −1 ) was found from the secondary source area. This highlights the capability of our method to distinguish between different emission areas of the landfill site, which can provide more detailed information about emission source apportionment compared to other methods deriving bulk emissions.

A decade of CH<sub>4</sub>, CO and N<sub>2</sub>O in situ measurements at Lauder, New Zealand: assessing the long-term performance of a Fourier transform infrared trace gas and isotope analyser

“…The audit results show the FTIR CO 2 and CH 4 measurements to be comparable to other measurement types (N 2 O and CO were not assessed). Other studies have shown the durability and reliability of the FTIR during field campaigns (Deutscher et al, 2010b;Laubach et al, 2016;Sonderfeld et al, 2017).…”

“…Second, it was to provide a complementary in situ measurement site to that at Baring Head,New Zealand (41.41 S,174.87 E, 85 m a. m. s. l.) (Brailsford et al, 2012) as a first step in a New Zealand carbon monitoring network. Measurements from these two sites have been used in a regional atmospheric inversion method determining CO 2 sinks and sources across New Zealand (Steinkamp et al, 2017).…”

“…Simplistic time series analysis is performed to provide an estimate of the annual trend and seasonal cycles and to ascertain if the FTIR can observe such atmospheric change on such timescales. Investigation into the FTIR CO 2 and δ 13 C-CO 2 measurement performance along with comparisons to co-located independent CO 2 (Steinkamp et al, 2017) and δ 13 C-CO 2 measurements will be reported in a separate study.…”

A measurement-based verification framework for UK greenhouse gas emissions: an overview of the Greenhouse gAs Uk and Global Emissions (GAUGE) project

“…rotary UAVs, to develop and refine new methods to use atmospheric measurements to quantify CH 4 and CO 2 emission from a landfill site (Riddick et al, 2016;Sonderfeld et al, 2017;Allen et al, 2017;Riddick et al, 2017). This represents one of the first demonstrations of using UAVs to sample GHG emissions.…”

“…Sonderfeld et al (2017) The underlying idea is that taking the ratio of the CH 4 and CO 2 fitted in nearby wavelength regions effectively removes spectral artefacts common to both CH 4 and CO 2 (e.g., scattering). The conventional method of using these data is to multiply the ratio by model CO 2 , assuming that CO 2 varies in space and time less than CH 4 .…”