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. © 2012, The Society of Agricultural Meteorology of Japan. All rights reserved.