EGU2020-12475
https://doi.org/10.5194/egusphere-egu2020-12475
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Urban Methane Surveys – A Case Study Where Isotope Measurements Guided Source Attribution

Bryce F.J. Kelly1, Xinyi (Lexie) Lu1, Zoë M. Loh2, and Rebecca E. Fisher3
Bryce F.J. Kelly et al.
  • 1School of Biological, Earth and Environmental Sciences, UNSW Sydney, 2052, NSW, Australia (bryce.kelly@unsw.edu.au; lexie.xinyilu@student.unsw.edu.au)
  • 2CSIRO Oceans & Atmosphere, Aspendale, Victoria, 3195, Australia (zoe.loh@csiro.au)
  • 3Royal Holloway, University of London, Egham Hill, Egham, Surrey TW20 0EX, United Kingdom (r.e.fisher@rhul.ac.uk)

Methane (CH4) is the second most important anthropogenic greenhouse gas after carbon dioxide (CO2) in the atmosphere1. Human activities are estimated to contribute ~50% of total CH4 emissions globally2. With 68% of the population projected to live in urban areas by 20503, there is a need to better quantify CH4 emissions from urban sources and to develop mitigation plans. Major potential urban sources include: the gas distribution network, landfills, the sewerage network, appliances in houses (heaters, stoves, hot-water systems), wood burning heaters, and urban wetlands.

This study aimed to determine the major CH4 sources in Melbourne (Australia’s second largest city with a population approaching 5 million people). Melbourne has grown rapidly since it was founded ~200 years ago and this has left legacy potential CH4 sources. For example, the gas distribution system has piping ranging from modern to 100 years old (common in unrenovated houses from early last century); landfills that use to be on the city fringe are now surrounded by new housing developments. 

To map the location of major CH4 sources throughout Melbourne we conducted a mobile survey, measuring the CH4 mole fraction ([CH4]) at a height of 3 m using a Los Gatos Research ultra-portable greenhouse gas analyser. An air inlet was attached to the roof of the car and the location of the measurements were georeferenced using a Hemisphere GPS system as we drove around the city. The day and night-time surveys were undertaken from the 26th – 27th July 2019 (winter).  When a major CH4 plume was detected 10 air samples were collected and stored 3 litre FlexFoil bags. These samples were analysed for [CH4], δ13C-CH4, [CO2], δ13C-CO2 using a Picarro G2201-i cavity ring-down spectrometer (CRDS). To determine the δ13C-CH4 signature of the plume each set of bags was analysed using a Miller-Tans plot and Bayesian regression. The combination of potential observable sources and the δ13C-CH4 signature was then used to attribute the source of the CH4 plume. We show that the δ13C-CH4 signatures of the CH4 plumes are needed to reduce the risk of attributing a plume to the wrong source. We present an example of separating domestic wood fires from a ‘super-emitter’ leak from the gas distribution system, and we also show how we traced a landfill plume for a distance of over 5 km using δ13C-CH4 measurements.

Our research demonstrates that mobile [CH4] surveys coupled with δ13C-CH4 analyses is a cost-effective workflow for mapping both diffuse CH4 emissions and ‘super-emitters’. Such surveys could be systematically undertaken in cities worldwide to delineate and prioritise targets for CH4 emission reduction. 

 

References

(1)      Myhre, G. et al. Cambridge University Press, 2013; Vol. 9781107057, pp 659–740.

(2)      Saunois, M. et al. Earth Syst. Sci. Data Discuss. 2019, 1–138.

(3)      United Nations. World Urbanization Prospects The 2018 Revision (ST/ESA/SER.A/420). 2019.

How to cite: Kelly, B. F. J., Lu, X. (., Loh, Z. M., and Fisher, R. E.: Urban Methane Surveys – A Case Study Where Isotope Measurements Guided Source Attribution, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12475, https://doi.org/10.5194/egusphere-egu2020-12475, 2020

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