| Abstract Title: | Identification of anthropogenic methane emitters in mixed source environments using vehicle platform, multiple instruments and multiple proxies: one set-up does not fit all. |
| Presenter Name: | Dr David Lowry |
| Co-authors: | Dr James France Dr Rebecca Fisher Ms Julianne Fernandez Dr Aliah al-Shalan Dr Semra Bakkaloglu Mr Mathias Lanoisell Ms Ceres Wooley-Maisch Prof Euan Nisbet |
| Company/Organisation: | Royal Holloway, University of London |
| Country: | United Kingdom |
Abstract Information :
The RHUL Greenhouse Gas Group has been carrying out vehicle surveys of methane emitters since 2013, augmented in 2020 by a dedicated survey vehicle and new suite of instruments MIGGAS. In terms of emissions assessment, the research in this field has been driven primarily by gas leak detection and quantification e.g. von Fischer et al., 2017; Weller et al., 2019, but recent papers have shown that many leak indicators LI in urban areas could well be emissions from waste water pipes Fernandez et al., 2022. This highlights the need in mixed-source environments to measure not just methane mole fractions, but other proxies that will identify source category. These include co-emitted gases, such as CO2, ethane C2H6, ammonia NH3, or methane isotopes 13C, 2H.rn rnAdditional consideration is given to air inlet height. While front bumper inlets at 30-80 cm work well for gas pipe leaks on roads driven, a vehicle rooftop inlet is a better option for more distal sources that could be beyond a 2m high roadside hedgerow, and in some instances up to 1km distant. Similarly driving speed has to be optimised for air inlet delays and instrument response time for accurate harmonisation with GPS to pinpoint plume positions.rnrnSurveys in 2021 used a selection of 4 different instruments, all measuring CH4 and other species or isotopes, and air sample collection for laboratory isotopic analysis. Data assessment to identify characteristics of each source type has allowed greater separation by emission category and subcategory. The 13C-enriched composition of distributed gas in the UK means that fugitive gas can be identified using low-precision mobile isotopic measurement when there is gt;1 ppm excess CH4 over background and reduced baseline noise. Gas distribution leaks can similarly be identified using C2H6:CH4 C2:C1 ratios, which fall in the range 0.03 to 0.09, much higher than biogenic and much lower than combustion sources.rnrnSeparation of waste and agricultural sources is more complex. Isotopic measurement can provide some separation of waste sources Bakkaloglu et al., 2022 and clearly distinguishes ruminant eructation from manure Lowry et al., 2020, but UK agricultural emissions are normally co-located breath and waste in cow barns. Co-emitted CO2 in breath makes CO2:CH4 ratios for cow barn plumes a potential discriminant, while in the absence of a NH3 analyser, a spectral interference on the C2H6 line, probably from NH3, produces a negative peak in manure emission plumes.rnrnAn ongoing further step ahead of flux calculation involves GPS location harmonisation of multiple-pass at 20-50 kph CH4 peaks from one 10 Hz and two 1 Hz instruments, and assessing the benefits of maximised peak height and complexity versus an optimised peak shape. The findings will allow an appropriate vehicle configuration, instrument array and driving speed to be selected for the target source types in each survey. rnrnBakkaloglu et al., 2022, Atmospheric Environment, in press, https:doi.org10.1016j.atmosenv.2022.119021rnFernandez et al., 2022, Atmospheric Environment X, 13, 100153, https:doi.org10.1016j.aeaoa.2022.100153 rnLowry et al., 2020, Science of the Total Environment, 708, 134600, https:doi.org10.1016j.scitotenv.2019.134600 rnvon Fischer et al., 2017, Environ. Sci. Technol. 51, 40914099, https:doi.org10.1021acs.est.6b06095 rnWeller et al., 2019, PLoS One 14, e0212287, https:doi.org10.1371journal.pone.0212287rn
