Proxies and uncertainties for 13C/12C ratios of atmospheric reactive gases emissions
Atmospheric Chemistry and Physics Discussions
We provide a comprehensive review of the proxy data on the <sup>13</sup>C/<sup>12</sup>C ratios and uncertainties of emissions of reactive carbonaceous compounds into the atmosphere, with a focus on CO sources. Based on an evaluated setup of the EMAC model, we derive the isotope-resolved dataset of its emission inventory for the 1997&ndash;2005 period. Additionally, we revisit the calculus required for the correct derivation of uncertainties associated with isotope ratios of emission
... of emission fluxes. The resulting overall surface CO emission δ<sup>13</sup>C in 2000 of &minus;(25.2&thinsp;±&thinsp;0.7)&thinsp;‰ is in line with the previous bottom-up estimates and a factor of two less uncertain. In contrast to this, we find that uncertainties of the respective inverse modelling estimates are substantially larger due to the correlated nature of their derivation. We reckon the δ<sup>13</sup>C values of surface emissions of higher hydrocarbons being within &minus;24&thinsp;‰ to &minus;27&thinsp;‰ (uncertainty typically below ±1&thinsp;‰), with an exception of isoprene emissions being close to &minus;30&thinsp;‰. The isotope signature of ethane surface emission coincides with earlier estimates, however integrating very different source inputs. δ<sup>13</sup>C values are reported relative to V-PDB.