Development of Fast Response Carbon Dioxide and Humidity Instrument

对大气表层二氧化碳湍流输送的准确测量有望实现对二氧化碳-气候问题的深入理解。涡旋相关技术是测量二氧化碳湍流传输的最有前途的技术。为了利用涡旋相关技术研究二氧化碳的传输，我们研制了用于测量二氧化碳和湿度同时波动的快速响应仪。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0.3ppm，湿度测量的噪声为0.01g/kg。仪器的漂移量分别为0.16ppm/h和0.01g kg/h。该仪器可用于不同地表条件下的野外实验：秸秆田、海面和植被覆盖的农田。为了研究二氧化碳的输送过程，用Tukey方案计算了垂直风速和二氧化碳脉动的WC同谱。值得注意的是，来自残茬田地的WE共谱被限制在0.02至0.1赫兹的窄范围内。二氧化碳湍流输送的平均值白天约为-0.05 mg；m^(-2)S^(-1)；夜间小于0.05 mg；m^(-2)S^(-1)。二氧化碳在海面上的湍流输送的原始值为-0.05~-0.17 mg&lt；m^(-2)S^(-1)。现场实验表明，该仪器可用于涡旋相关技术与声速风速仪相结合的二氧化碳和湿度通量的测量。

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.