Development of Fast Response Carbon Dioxide and Humidity Instrument

近地层CO2湍流输送的精确测量有望加深对CO2-气候问题的认识。涡动相关技术是测量CO2湍流输送最有前途的技术。为了利用涡动相关技术研究大气中二氧化碳的输运，我们研制了一台快速响应的二氧化碳和湿度同步波动测量仪。测量频率为30 Hz，传感路径长度为20 cm。二氧化碳测量的噪声为0.3 ppm，湿度测量的噪声为0.01 g/kg。该仪器的漂移量分别为0.16ppm/h和0.01g/kg/h，并在不同地表条件下进行了田间试验：残茬田、海面和植被田。本文用Tukey方案计算了垂直风速和CO2脉动的wc-余谱，以研究CO2的输送过程。注意到，来自茬地的w-cospectrum被限制在0.02至0.1Hz的窄范围内。白天湍流输送的平均值约为-0.05 mg <m^（-2）s^（-1）>，夜间小于0.05 mg <m^（-2）s^（-1）>。海面CO2湍流输运的原始值为负的-0.05 ~-0.17 mg <m^（-2）s^（-1）> .现场实验表明，本仪器是一种很有前途的涡动相关技术结合声波风速计测量CO2通量和湿度的仪器.

The accurate measurement of turbulent transport of carbon dioxide in the atmospheric surface layer has been expected to achieve deep understanding of the carbon dioxide - climate ploblem. The eddy correlation technique is the most promising one to measure turbulent transport of carbon dioxide. In order to investigate carbon dioxide transport by the eddy correlation technique, we developed the fast response instrument designed to measure simultaneous fluctuations of carbon dioxide and humidity. The measuring frequency is 30 Hz and the sensing path length is 20 cm. The noise is 0.3 ppm for carbon dioxide measurement and 0.01 g/kg for humidity measurement. The drift of the instrument is about 0.16 ppm/h and 0.01 g kg/h, respectively.The instrument is applied to the field experiments under various surface conditions: stubble field, sea surface and vegetated fields. The wc-cospectra of vertical wind velocity and carbon dioxide fluctuations are calculated by Tukey's scheme in order to investigate the carbon dioxide transport processes. It is noted that the we-cospectra from the stubble field are confined to a narrow range of 0.02 to 0.1 Hz. The average values of turbulent transport of carbon dioxide are about -0.05 mg <m^(-2)s^(-1)> in the daytime and less than 0.05 mg <m^(-2)s^(-1)> in the nighttime. The raw values of turbulent transport of carbon dioxide over sea surface are negative of -0.05 to -0.17 mg <m^(-2)s^(-1)> .Field experiments show that the present instrument is promising for flux measurements of carbon dioxide and humidity by the eddy correlation technique in conjunction with a sonic anemometer.