The CO₂ budget and rectification airborne study: Strategies for measuring rectifiers and regional fluxes

Temporal covariations between atmospheric transport and surface gas fluxes, known as rectifier effects, may lead to significant spatial variations in CO₂ and other gases. Attempts to constrain carbon fluxes using surface background measurements and inverse methods are limited by large uncertainties in these effects. Airborne measurements of the vertical and horizontal distributions of CO₂, CO, O₂, and other tracers have the potential to significantly reduce these uncertainties. In this paper, we discuss observational requirements for quantifying rectifier effects and estimating regional fluxes, and use existing temperate and tropical forest data and model simulations to investigate the most promising measurement strategies. Using relationships between multiple tracers, it should be possible to separate the terrestrial, oceanic, and industrial influences on observed horizontal and vertical CO₂ variations. Summer observations of terrestrial CO₂ signals over land would then provide a direct measure of the diurnal rectifier effect, while comparisons between summer and winter observations would constrain the seasonal rectifier. We have plans for such measurements over North America and the adjacent ocean regions using airborne instrumentation and flask samples, as part of the CO₂ Budget and Rectification Airborne Study. The analyses presented here provide preliminary tests of our measurement approach and reveal evidence of strong diurnal rectifier effects.