Comparison of Ozone Fluxes over a Maize Field Measured with Gradient Methods and the Eddy Covariance Technique

Ozone(O) fluxes were measured over a maize field using the eddy covariance(EC) technique and gradient methods.The main objective was to evaluate the performance of the gradient methods for measuring the Oflux by comparing them with the EC Oflux.In this study,turbulent exchange coefficients(K) calculated with three methods were compared.These methods were the aerodynamic gradient(AG) method(in which K is calculated by using wind speed and temperature gradients),the aerodynamic gradient combined with EC(AGEC) method,in which the friction velocity and other variables are based on EC measurements,and the modified Bowen ratio using the EC sensible heat flux and temperature gradient(MBR) method.Meanwhile,the effects of the measurement and calculation methods of the Oconcentration gradient were analyzed.The results showed that:(1) on average,the transfer coefficient computed by the MBR method was 40% lower,and the coefficient determined with the AG method was 25% higher,than that determined with the AGEC method.(2) The gradient method’s Ofluxes with the MBR,AGEC,and AG methods were 30.4% lower,11.7% higher,and 45.6% higher than the EC Oflux,respectively.(3) The effect of asynchronous Oconcentration measurements on the Ogradient must be eliminated when using one analyzer to cyclically measure two-level Oconcentrations.The accuracy of gradient methods for Oflux is related to the exchange coefficient calculation method,and its precision mainly depends on the quality of the Ogradient.