Reduced Methane Emissions from Santa Barbara Marine Seeps

The article of record as published may be found at http://dx.doi.org/10.3390/rs9111162Airborne in situ and remote sensing measurements of methane were performed over the marine seeps in the Santa Barbara Channel close to the Coal Oil Point in California on two days in June and August 2014 with the aim to re-assess their methane emissions. During this period, methane column averaged dry air mole fractions derived from airborne remote sensing measurements in the short-wave infrared and airborne in situ measurements of methane indicate that emissions are 2–6 kt CH4 y¯1, significantly lower than expected from previous publications. This is also confirmed by the on ground in situ measurement time series recorded at the onshore West Campus Monitoring Station in Santa Barbara. Using a time series of methane data, a decline in methane concentrations between 2008 and 2015 of more than a factor of two was derived for air masses originating from the seep field direction.NASA Earth Science Division, Research and Analysis ProgramNNX13AM21

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

The article of record as published may be found at https://dx.doi.org/10.5194/amt-10-3429-2017The Supplement related to this article is available online at https://doi.org/10.5194/amt-10-3429-2017-supplementFugitive 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 ktCH₄ 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 ktCH₄ yr ¯¹ (±2.8 ktCH₄ yr ¯¹). The US Environmental Protection Agency (EPA) reported inventory value is 11.5 ktCH₄ yr ¯¹ for 2014, on average 2.8 ktCH₄ yr ¯¹ (±1.6 ktCH₄ 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.NASA AMESCIRPASGFZ German Research Centre for GeosciencesUniversity and State of Bremen and the Helmholtz Center PotsdamEuropean Space Agency (ESA)National Aeronautics and Space Administration (NASA

Reduced Methane Emissions from Santa Barbara Marine Seeps

Airborne in situ and remote sensing measurements of methane were performed over the marine seeps in the Santa Barbara Channel close to the Coal Oil Point in California on two days in June and August 2014 with the aim to re-assess their methane emissions. During this period, methane column averaged dry air mole fractions derived from airborne remote sensing measurements in the short-wave infrared and airborne in situ measurements of methane indicate that emissions are 2–6 kt CH 4 y − 1 , significantly lower than expected from previous publications. This is also confirmed by the on ground in situ measurement time series recorded at the onshore West Campus Monitoring Station in Santa Barbara. Using a time series of methane data, a decline in methane concentrations between 2008 and 2015 of more than a factor of two was derived for air masses originating from the seep field direction