Methane emissions in Kuwait: Plume identification, isotopic characterisation and inventory verification

The distribution of methane sources in Kuwait was mapped through mobile vehicle surveying of methane mole fraction, and by collection of air samples at source for subsequent isotopic analysis. Mobile plume identification and isotopic analysis, reveals that by far the largest observed source of methane in Kuwait is from landfill sites (delta C-13(CH4) of -58 parts per thousand), with smaller contributions from fossil fuel industry (-50 parts per thousand), wastewater treatment (-49 parts per thousand) and ruminant animals (sheep-64 parts per thousand, cows, -62 parts per thousand, camels-60 parts per thousand). Regular weekly air samples were collected over two years from three sites in Kuwait, one NW of the city, one to the SE and one in the city from the rooftop of the Kuwait College of Science. Associated with higher mole fraction is a consistent depletion in C-13 of methane, pointing to a national source mix with delta C-13(CH4) of -55.9 parts per thousand. This is significantly different from calculations using EDGAR v.5 inventory that suggest a source mix of-52.8 parts per thousand. Diurnal campaigns from a city location confirm that the sources are dominantly biogenic (-59 to -56 parts per thousand) in and around the urban areas. The EDGAR 5.0 inventory suggests that the dominant sources of methane in Kuwait are leaks from gas flaring and fossil fuel distribution, with additional smaller emissions from landfills, sewage (wastewater) treatment and ruminant animals, but with a waste component increasing relative to fossil fuel emissions in recent decades. Measurements during 2015 and 2016 suggest that for all but the far south and SW of the country which is not in the meteorological footprint of fixed site or mobile measurement, there is a dominant waste source and much smaller observed proportion from fossil fuel activities. This research demonstrates for the first time in Kuwait that continuous mobile measurements for plume identification coupled with high-precision isotopic analysis using CF-GC-IRMS (Continuous Flow Gas Chromatography-Isotope Ratio Mass Spectrometry) is an effective way of identifying methane sources and understanding their relative contributions. To unambiguously quantify relative contributions will require further work, particularly in the SW region of the country, utilizing aircraft and/or satellite retrievals. The results of this research will contribute to understanding the methane budget of this poorly studied region.