Methane emissions from a Californian landfill, determined from airborne remote sensing and in situ measurements

Abstract

Abstract. Fugitive emissions from waste disposal sites are important anthropogenic sources of the greenhouse gas methane (CH4). As a result of the growing world population and the recognition of the need to control greenhouse gas emissions, this anthropogenic source of CH4 has received much recent attention. However, the accurate assessment of the CH4 emissions from landfills by modeling and existing measurement techniques is challenging. This is because of inaccurate knowledge of the model parameters and the extent of and limited accessibility to landfill sites. This results in a large uncertainty in our knowledge of the emissions of CH4 from landfills and waste management. In this study, we present results derived from data collected during the research campaign COMEX (CO2 and MEthane eXperiment) in late summer 2014 in the Los Angeles (LA) Basin. One objective of COMEX, which comprised aircraft observations of methane by the remote sensing Methane Airborne MAPper (MAMAP) instrument and a Picarro greenhouse gas in situ analyzer, was the quantitative investigation of CH4 emissions. Enhanced CH4 concentrations or CH4 plumes were detected downwind of landfills by remote sensing aircraft surveys. Subsequent to each remote sensing survey, the detected plume was sampled within the atmospheric boundary layer by in situ measurements of atmospheric parameters such as wind information and dry gas mixing ratios of CH4 and carbon dioxide (CO2) from the same aircraft. This was undertaken to facilitate the independent estimation of the surface fluxes for the validation of the remote sensing estimates. During the COMEX campaign, four landfills in the LA Basin were surveyed. One landfill repeatedly showed a clear emission plume. This landfill, the Olinda Alpha Landfill, was investigated on 4 days during the last week of August and first days of September 2014. Emissions were estimated for all days using a mass balance approach. The derived emissions vary between 11.6 and 17.8 kt CH4 yr−1 with related uncertainties in the range of 14 to 45 %. The comparison of the remote sensing and in situ based CH4 emission rate estimates reveals good agreement within the error bars with an average of the absolute differences of around 2.4 kt CH4 yr−1 (±2. 8 kt CH4 yr−1). The US Environmental Protection Agency (EPA) reported inventory value is 11.5 kt CH4 yr−1 for 2014, on average 2.8 kt CH4 yr−1 (±1. 6 kt CH4 yr−1) lower than our estimates acquired in the afternoon in late summer 2014. This difference may in part be explained by a possible leak located on the southwestern slope of the landfill, which we identified in the observations of the Airborne Visible/Infrared Imaging Spectrometer – Next Generation (AVIRIS-NG) instrument, flown contemporaneously aboard a second aircraft on 1 day.

Using remote sensing to detect, validate, and quantify methane emissions from California solid waste operations

“…Remote sensing of methane emissions with high spatial resolution is now a possibility with advances in airborne and satellite instrument technology , Thompson et al 2016, Cusworth et al 2019. Previous studies have shown that methane emissions from individual landfills are detectable by airborne imaging spectrometers (Krautwurst et al 2017;Duren et al 2019). This new observing capability opens up the possibility to quantify and validate methane emissions that result from landfill management practices.…”

Methane emissions from underground gas storage in California

“…The AVIRIS-C and AVIRIS-NG methane retrieval is based on absorption spectroscopy between 2100 and 2500 nm and uses a linearized matched filter to calculate a mixing ratio length in units of ppm-m representing the thickness and concentration within a volume of equivalent absorption (Thompson et al 2015). This and related techniques have been demonstrated in a number of previous airborne campaigns (Thompson et al 2015, Thompson et al 2016, Thorpe et al 2017, Krautwurst et al 2017, Duren et al 2019. Thorpe et al (2016) demonstrated that plumes for controlled releases as low as 10 kgCH 4 h −1 were consistently observed by AVIRIS-NG across multiple flight altitudes and wind conditions and a minimum detection limit of 2 kgCH 4 h −1 .…”

A Near-Field Gaussian Plume Inversion Flux Quantification Method, Applied to Unmanned Aerial Vehicle Sampling

“…Far-field (defined here as > 1 km from source) in-situ sampling on a downwind two-dimensional vertical flux plane, roughly perpendicular to mean wind direction, has successfully been used to calculate fluxes using mass balance box modelling [40][41][42]. These previous far-field studies utilised geospatial kriging [43] to interpolate between sparse spatial sampling of a well-defined emission plume, characterised by dispersion [20].…”