Linking emissions of fossil fuel CO₂ and other anthropogenic trace gases using atmospheric ¹⁴CO₂

[1] Atmospheric CO₂ gradients are usually dominated by the signal from net terrestrial biological fluxes, despite the fact that fossil fuel combustion fluxes are larger in the annual mean. Here, we use a six year long series of ¹⁴CO₂ and CO₂ measurements obtained from vertical profiles at two northeast U.S. aircraft sampling sites to partition lower troposphere CO₂ enhancements (and depletions) into terrestrial biological and fossil fuel components (C_bio and C_ff). Mean C_ff is 1.5 ppm, and 2.4 ppm when we consider only planetary boundary layer samples. However, we find that the contribution of C_bio to CO₂ enhancements is large throughout the year, and averages 60% in winter. Paired observations of C_ff and the lower troposphere enhancements (Δ_gas) of 22 other anthropogenic gases (CH₄, CO, halo- and hydrocarbons and others) measured in the same samples are used to determine apparent emission ratios for each gas. We then scale these ratios by the well known U.S. fossil fuel CO₂ emissions to provide observationally based estimates of national emissions for each gas and compare these to “bottom up” estimates from inventories. Correlations of Δ_gas with C_ff for almost all gases are statistically significant with median r²for winter, summer and the entire year of 0.59, 0.45, and 0.42, respectively. Many gases exhibit statistically significant winter:summer differences in ratios that indicate seasonality of emissions or chemical destruction. The variability of ratios in a given season is not readily attributable to meteorological or geographic variables and instead most likely reflects real, short-term spatiotemporal variability of emissions.