Chen, B., J.M. Chen, J. Liu, D. Chan, K. Higuchi, and A. Shashkov, 2004. A vertical diffusion scheme to estimate the atmospheric rectifier effect, Journal of Geophysical Research D: Atmospheres, 109 (D4), 1-22 (doi:10.1029/2003JD003925).

The magnitude and spatial distribution of the carbon sink in the extratropical Northern Hemisphere remain uncertain in spite of much progress made in recent decades. Vertical CO 2 diffusion in the planetary boundary layer (PBL) is an integral part of atmospheric CO 2 transport and is important in understanding the global CO 2 distribution pattern, in particular, the rectifier effect on the distribution [Keeling et al., 1989 ; Denning et al., 1995]. Attempts to constrain carbon fluxes using surface measurements and inversion models are limited by large uncertainties in this effect governed by different processes. In this study, we developed a Vertical Diffusion Scheme (VDS) to investigate the vertical CO 2 transport in the PBL and to evaluate CO 2 vertical rectification. The VDS was driven by the net ecosystem carbon flux and the surface sensible heat flux, simulated using the Boreal Ecosystem Productivity Simulator (BEPS) and a land surface scheme. The VDS model was validated against half‐hourly CO 2 concentration measurements at 20 m and 40 m heights above a boreal forest, at Fraserdale (49°52?29.9?N, 81°34?12.3?W), Ontario, Canada. The amplitude and phase of the diurnal/seasonal cycles of simulated CO 2 concentration during the growing season agreed closely with the measurements (linear correlation coefficient (R) equals 0.81). Simulated vertical and temporal distribution patterns of CO 2 concentration were comparable to those measured at the North Carolina tower. The rectifier effect, in terms of an annual‐mean vertical gradient of CO 2 concentration in the atmosphere that decreases from the surface to the top of PBL, was found at Fraserdale to be about 3.56 ppmv. Positive covariance between the seasonal cycles of plant growth and PBL vertical diffusion was responsible for about 75% of the effect, and the rest was caused by covariance between their diurnal cycles. The rectifier effect exhibited strong seasonal variations, and the contribution from the diurnal cycle was mostly confined to the surface layer (less than 300 m).