Development of Fast Response Carbon Dioxide and Humidity Instrument

对大气表层二氧化碳湍流输运的精确测量有望实现对二氧化碳-气候问题的深刻认识。涡流相关技术是测量二氧化碳湍流输运最有前途的方法。为了利用涡旋相关技术研究大气中二氧化碳的输运，我们研制了快速响应仪，用于同时测量大气中二氧化碳和湿度的波动。测量频率为30hz，传感路径长度为20cm。二氧化碳测量噪声为0.3 ppm，湿度测量噪声为0.01 g/kg。仪器的漂移分别约为0.16 ppm/h和0.01 g kg/h。该仪器适用于秸秆田、海面、植被田等不同地表条件下的田间试验。为了研究二氧化碳的输运过程，采用Tukey方案计算了垂直风速和二氧化碳波动的wc-共谱。我们注意到，残茬场的自共谱被限制在0.02 ~ 0.1 Hz的狭窄范围内。白天二氧化碳湍流输运的平均值约为-0.05 mg <m^(-2)s^(-1)>，夜间小于0.05 mg <m^(-2)s^(-1)>。二氧化碳在海面上湍流输运的原始值为负-0.05 ~ -0.17 mg <m^(-2)s^(-1)>。现场试验表明，该仪器可与声速风速仪结合使用涡流相关技术测量二氧化碳和湿度的通量。

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.