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

Surface fluxes of O-3, 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 O-3, 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. (C) 2000 Elsevier Science Ltd. All rights reserved.