Radiocarbon (14C) Traces the Fossil and Biogenic Components of Total CO2
J.B. Miller1, S. Lehman2, S. Montzka3, P. Tans3, C. Sweeney1, B. Miller1, L. Miller3, J. Turnbull3 and C. Wolak2
1Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309; 303-497-7739, E-mail: email@example.com
2Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO 80309
3NOAA Earth System Research Laboratory, Boulder, CO 80305
Δ14C, the ratio of radiocarbon to total carbon, is a theoretically ideal tracer for recently added fossil fuel CO2, because fossil fuel is 14C-free. In contrast, all other carbon reservoirs that exchange CO2 with the atmosphere, like the terrestrial biosphere and the oceans, are relatively rich in 14C. Since 2004, NOAA ESRL and the University of Colorado Institute for Arctic and Alpine Research (INSTAAR) Radiocarbon Laboratory have worked together to make high precision (< 2 ‰) Δ14C measurements. Our two sites in the eastern USA, Portsmouth, NH (NHA) and Cape May, NJ (CMA) exhibit large CO2 signals from anthropogenic and biogenic fluxes. Using Δ14CO2, however, we are able to partition the boundary layer CO2 signal into biogenic and fossil fuel components. Once separated, these signals are independently useful. The biological signal can be used directly to infer the uptake and release of carbon by the biosphere, and the fossil signal can constrain anthropogenic emissions of CO2, without the use of inventories, which can never be as recent as the measurements. Furthermore, the derived fossil fuel CO2 signal is closely related to boundary layer enhancements of many air quality tracers like CO, SF6, CFC-replacement compounds, and solvents like benzene. These relationships can exist for total CO2, but we will show that they are biased because of the biogenic contribution. Having established a relationship between fossil fuel CO2 and these tracers, we estimate their emissions by scaling the measured fossil-CO2 tracer emission ratios to the well-known U.S. fossil fuel CO2 inventory. Finally, we will show that a multi-tracer proxy of fossil CO2 can be formed from the observed correlations. Such a multi-proxy tracer might serve as a low cost and widespread adjunct to actual 14C observations.