Vertical profiles of biospheric and fossil fuel-derived CO2 and fossil fuel CO2: CO ratios from airborne measurements of Δ14C, CO2 and CO above Colorado, USA

Abstract

Measurements of Δ14C in atmospheric CO2 are an effective method of separating CO2 additions from fossil fuel and biospheric sources or sinks of CO2. We illustrate this technique with vertical profiles of CO2 and Δ14C analysed in whole air flask samples collected above Colorado, USA in May and July 2004. Comparison of lower tropospheric composition to cleaner air at higher altitudes (>5 km) revealed considerable additions from respiration in the morning in both urban and rural locations. Afternoon concentrations were mainly governed by fossil fuel emissions and boundary layer depth, also showing net biospheric CO2 uptake in some cases. We estimate local industrial CO2:CO emission ratios using in situ measurements of CO concentration. Ratios are found to vary by 100% and average 57 mole CO2:1 mole CO, higher than expected from emissions inventories. Uncertainty in CO2 from different sources was ±1.1 to ±4.1 ppm for addition or uptake of -4.6 to 55.8 ppm, limited by Δ14C measurement precision and uncertainty in background Δ14C and CO2 levels. © 2009 The Authors Journal compilation © 2009 Blackwell Munksgaard.