MAY 2004: Constraints on regional carbon fluxes from CO2:CO correlations in Asian outflow

The left-hand panel shows a range of regional CO2/CO emissions ratios, (plotted as slopes) based on bottom-up emissions inventories. The CO2/CO emission ratio varies with the source of CO2 (e.g., differences in combustion efficiency vs. terrestrial biospheric flux) and provides a characteristic signature of source regions and source type. The right-hand panel shows CO2:CO correlations in Asian outflow measured on DC-8 Flight 16 (March 29, 2001) of the TRACE-P campaign out of Japan. Distinct correlations were observed, typical of the majority of TRACE-P flights. Highest CO2:CO slopes were observed over Japan (where CO emissions are regulated) and lower slopes characterized Chinese boundary layer outflow. The analysis of Suntharalingam et al. [2004] employs these observed CO2:CO correlations from the TRACE-P aircraft campaign together with a 3-D global chemical transport model (GEOS-CHEM), to constrain specific components of the East Asian CO2. Model simulations using best a priori estimates of regional CO2 and CO sources overestimate CO2 concentrations and CO2:CO slopes in Asian boundary layer outflow. Constraints from observed CO2:CO slopes indicate that this must arise from an overestimate of the modeled Chinese biospheric CO2 flux. Our corrected best estimate of the net biospheric source of CO2 from China for March-April 2001 is 3200 Gg C/day, which represents a 45% reduction of the a priori flux.