LAUSR

Ozone (O 3 ) 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 O 3 flux by comparing them with the EC O 3 flux. 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 O 3 concentration 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 O 3 fluxes with the MBR, AGEC, and AG methods were 30.4% lower, 11.7% higher, and 45.6% higher than the EC O 3 flux, respectively. (3) The effect of asynchronous O 3 concentration measurements on the O 3 gradient must be eliminated when using one analyzer to cyclically measure two-level O 3 concentrations. The accuracy of gradient methods for O 3 flux is related to the exchange coefficient calculation method, and its precision mainly depends on the quality of the O 3 gradient. 近地层臭氧通量不仅能帮助人们理解臭氧的沉积过程,而且可以更好地评估臭氧对生态系统的影响。涡度相关技术是测量湍流通量最好的方法,但该技术现在还没有被广泛地应用于臭氧通量观测,而梯度法在这方面仍然有一定的应用价值。为了评估梯度法在测量臭氧通量方面的表现,我们利用梯度法和涡度相关技术在玉米地上同时观测了臭氧通量。本研究主要比较了三种湍流交换系数(K)的计算方法对臭氧通量结果的影响。第一种是传统的空气动力学梯度方法(AG),该方法中K值是直接利用风速和温度梯度来计算的。第二种是AG与涡度相关技术(EC)结合的方法(AGEC),该方法利用一些常规的EC数据来计算K值;第三种是修订波文比方法(MBR),该方法利用显热通量和温度梯度计算K值。同时,我们分析讨论了不同臭氧浓度梯度测量和计算方法对梯度结果的影响。结果表明:(1)用MBR法计算的K值比用AGEC法计算的K值平均低40%,而AG法计算的K值比用AGEC法得到的K值平均高25%。(2)用MBR法、AGEC法和AG法计算的臭氧通量比用EC法观测的臭氧通量分别低30.4%、高11.7%和高45.6%。AGEC方法计算的臭氧通量最接近EC观测的结果,相对而言是计算K值最好的方法。(3)当用一台臭氧分析仪循环测量两个高度上的臭氧浓度来计算梯度时,必须考虑消除臭氧浓度非同步测量对臭氧梯度的影响。用梯度法估算臭氧通量的准确度与交换系数计算方法有关,而其精度主要取决于臭氧梯度的数据质量。