Experimental validation of WPL correction for CO₂ flux by eddy covariance technique over the asphalt surface

Abstract

We experimentally validated the density correction (called WPL or Webb correction) over the dry asphalt surface by simultaneously measuring CO₂ fluxes by closed-path eddy covariance and closed-chamber techniques, which is inescapable for evaluating the surface CO₂ flux by the open-path eddy covariance technique. The total CO₂ flux with WPL correction by the open-path eddy covariance technique was evaluated as a systematically small upward flux, which was consistent with that of our previous study. The instrumental error of the sonic anemometers and the additional heating correction for the open-path gas analyzer were not potential sources of total upward CO₂ fluxes. The CO₂ flux by the closed-chamber technique was also an upward flux; however, it was three orders of magnitude smaller than the total CO₂ flux by the open-path eddy covariance technique. The CO₂ flux calculated from the CO₂ mixing ratio by the closed-path eddy covariance technique was almost zero. Our results suggest the possible upward overestimation of the total CO₂ flux with the WPL correction by the open-path eddy covariance technique.