Studies of the global carbon cycle are motivated by the need to predict future trends in atmospheric carbon dioxide (CO2), to define responses of the terrestrial biosphere and oceans to changing CO2 and climate. Currently the best constraints on marine and terrestrial fluxes are derived by inverse analysis, where concentration data for CO2 and other species from global surface observations are analyzed using global models of biogeochemistry and atmospheric transport. One of the largest sources of uncertainty for current inverse studies is the "rectification" of seasonal and diurnal oscillations of CO2 fluxes, in which correlation between biophysical fluxes and rates for transport produce large scale, stationary concentration gradients in the atmosphere; validation data for this phenomenon are currently unavailable. This study will provide comprehensive data of the CO2 gradients due to rectification. This will be accomplished via airborne measurements of CO2, CO (carbon monoxide), SF6 (sulfur hexafluoride), 13CO2, and other tracers in and above the planetary boundary layer (PBL) over North America and adjacent ocean regions in two campaigns (summer and winter), supplemented by intensive diurnal observations in and above the PBL in selected regions. This project is supported jointly by NSF, DOE, NASA and NOAA.
