Articles | Volume 17, issue 13
Research article
13 Jul 2017
Research article |  | 13 Jul 2017

Uncertainties of fluxes and 13C  ∕ 12C ratios of atmospheric reactive-gas emissions

Sergey Gromov, Carl A. M. Brenninkmeijer, and Patrick Jöckel

Abstract. We provide a comprehensive review of the proxy data on the 13C ∕ 12C ratios and uncertainties of emissions of reactive carbonaceous compounds into the atmosphere, with a focus on CO sources. Based on an evaluated set-up of the EMAC model, we derive the isotope-resolved data set of its emission inventory for the 1997–2005 period. Additionally, we revisit the calculus required for the correct derivation of uncertainties associated with isotope ratios of emission fluxes. The resulting δ13C of overall surface CO emission in 2000 of −(25. 2 ± 0. 7) ‰ is in line with previous bottom-up estimates and is less uncertain by a factor of 2. In contrast to this, we find that uncertainties of the respective inverse modelling estimates may be substantially larger due to the correlated nature of their derivation. We reckon the δ13C values of surface emissions of higher hydrocarbons to be within −24 to −27 ‰ (uncertainty typically below ±1 ‰), with an exception of isoprene and methanol emissions being close to −30 and −60 ‰, respectively. The isotope signature of ethane surface emission coincides with earlier estimates, but integrates very different source inputs. δ13C values are reported relative to V-PDB.

Short summary
We revisit the proxies/uncertainties for the 13C/12C ratios of emissions of reactive C into the atmosphere. Our main findings are (i) a factor of 2 less uncertain estimate of tropospheric CO surface sources δ13C, (ii) a confirmed disagreement between the bottom-up and top-down 13CO-inclusive emission estimates, and (iii) a novel estimate of the δ13C signatures of a range of NMHCs/VOCs to be used in modelling studies. Results are based on the EMAC model emission set-up evaluated for 2000.
Final-revised paper