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.