An Approach to Minimizing Artifacts Caused by Cross-Sensitivity in the Determination of Air-Sea CO_2 Flux Using the Eddy-Covariance Technique

摘要

The air-sea CO_2 flux was measured from a research vessel in the North Yellow Sea in October 2007 using an open-path eddy-covariance technique. In 11 out of 64 samples, the normalized spectra of scalars (CO_2, water vapour, and temperature) showed similarities. However, in the remaining samples, the normalized CO_2 spectra were observed to be greater than those of water vapour and temperature at low frequencies. In this paper, the noise due to cross-sensitivity was identified through a combination ofintercomparisons among the normalized spectra of three scalars and additional analyses. Upon examination, the cross-sensitivity noise appeared to be mainly present at frequencies <0.8 Hz. Our analysis also suggested that the high-frequency fluctuationsof CO_2 concentration (frequency >0.8 Hz) was probably less affected by the cross-sensitivity. To circumvent the cross-sensitivity issue, the cospectrum in the high-frequency range 0.8-1.5 Hz, instead of the whole range, was used to estimate the CO_2 flux by taking the contribution of the high frequency to the CO_2 flux to be the same as the contribution to the water vapour flux. The estimated air-sea CO_2 flux in the North Yellow Sea was —0.039 ± 0.048 mg m~(-2) s~(-1), a value comparable to the estimates using the inertial dissipation method and Edson's method (Edson et al., J Geophys Res 116:C00F10, 2011).