We revisit the proxies/uncertainties for the 13
C ratios of emissions of reactive C into the atmosphere. Our main findings/results are: (i) A factor of 2 less uncertain estimate of tropospheric CO surface sources δ13
C, (ii) A confirmed disagreement between the bottom-up and top-down 13
CO-inclusive emission estimates, and (iii) A novel estimate of the δ13
C signatures of a range of NMHCs/VOCs to be used in modelling studies. Results are based on the EMAC model emission setup evaluated for 2000.