Computing surface concentration fluxes of trace gases from a variational method using measured variance and single-level concentration data

Surface fluxes of O3, CO2 and SO2 were estimated from a variational method by using measured concentrations and variances of these trace gases. The measurements were taken over a deciduous forest when it was fully leafed during the summer of 1988 and when it was leafless during the winter of 1990. A flux–variance relation and a flux–gradient relation were employed as constraints in a cost function which is minimized to find the optimal estimate of concentration fluxes of the gases under study. Fluxes of O3, CO2 and SO2 from the variational method were compared with fluxes estimated by the flux–variance relation and measured using an eddy correlation technique. Results show that the variational method improves the estimates of fluxes.