Radiocarbon Measurements Reveal Underestimated Fossil CH4 and CO2 Emissions in London

Radiocarbon (C-14) is a powerful tracer of fossil emissions because fossil fuels are entirely depleted in C-14, but observations of (CO2)-C-14 and especially (CH4)-C-14 in urban regions are sparse. We present the first observations of C-14 in both methane (CH4) and carbon dioxide (CO2) in an urban area (London) using a recently developed sampling system. We find that the fossil fraction of CH4 and the atmospheric concentration of fossil CO(2 )are consistently higher than simulated values using the atmospheric dispersion model NAME coupled with emission inventories. Observed net biospheric uptake in June-July is not well correlated with simulations using the SMURF model with NAME. The results show the partitioning of fossil and biospheric CO2 and CH4 in cities can be evaluated and improved with C-14 observations when the nuclear power plants influence is negligible.