The concentration of atmospheric methane (CH4) has more than doubled over the industrial era. To help constrain global and regional CH4 budgets, inverse (top-down) models incorporate data on the concentration and stable carbon (δ13C) and hydrogen (δ2H) isotopic ratios of atmospheric CH4. These models depend on accurate δ13C and δ2H end-member source signatures for each the main emissions categories. Compared with meticulous measurement and calibration of isotopic CH4 in the atmosphere, there has been relatively little effort to characterize globally representative isotopic source signatures, particularly for fossil fuel sources, since the 1980s. Most global CH4 budget models have so far relied on outdated source signature values derived from globally non-representative data. To correct this deficiency, we present a comprehensive, globally representative end-member database of the δ13C and δ2H of CH4 from fossil fuel (conventional natural gas, shale gas and coal), modern microbial (wetlands, rice paddies, ruminants, termites, and landfills/waste) and biomass burning sources. Alkane and permanent gas molecular chemistry for fossil fuel categories are also included with the database. The database comprises 10,706 samples (8,732 fossil fuel, 1972 non-fossil) from 190 published references. Mean (unweighted) δ13C signatures for fossil fuel CH4 are significantly lighter than values commonly used in CH4 budget models, thus highlighting potential under-estimation of fossil fuel CH4 emissions in previous CH4 budget models. This living database will be updated every 2-3 years to provide the atmospheric modeling community with the most complete CH4 source signature data possible.
This 2017 version of the gas geochemistry database supersedes an earlier version (Sherwood, O. A., Schwietzke, S. S., Arling, V. A., and Etiope, G.: Global Inventory of Fossil and Non-fossil Methane δ13C Source Signature Measurements for Improved Atmospheric Modeling. Available at: https://doi.org/10.15138/G37P4D, 2016).
The following updates have been made to the 2017 version:
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