An innovative eddy-covariance system with vortex intake for measuring carbon dioxide and water fluxes of ecosystems
Jingyong Ma1,2, Tianshan Zha1,2, Xin Jia1,2, Steve Sargent3, Rex Burgon3, Charles P.-A. Bourque4, Xinhua Zhou3, Peng Liu1,2, Yujie Bai1,2, and Yajuan Wu1,21School of Soil and Water Conservation, Beijing Forestry University, Beijing, China 2Beijing Engineering Research Center of Soil and Water Conservation, Beijing Forestry University, Beijing, China 3Campbell Scientific, Inc., Logan UT, USA 4Faculty of Forestry and Environmental Management, 28 Dineen Drive, University of New Brunswick, Fredericton, New Brunswick, Canada
Received: 26 Aug 2016 – Accepted for review: 25 Oct 2016 – Discussion started: 01 Nov 2016
Abstract. Closed-path eddy-covariance (EC) systems are used to monitor exchanges of carbon dioxide (CO2) and water vapor (H2O) between the atmosphere and biosphere. Traditional EC intake systems are equipped with in-line filters to prevent airborne dust particulates from contaminating the optical windows of the sample cell which degrades measurements. In order to preserve fast-frequency response, the in-line filter should be small, but small filters plug quickly and require frequent replacement. This paper reports the test results of a field-performance of an innovative EC system (EC155, Campbell Scientific, Inc.) with a prototype vortex intake replacing the in-line filter of a traditional EC system. The vortex intake design is based on fluid dynamics theory. An air sample is drawn into the vortex chamber, where it spins in a vortex flow. The initially homogenous flow is separated when particle momentum forces heavier particles to the periphery of the chamber, leaving a much cleaner air stream at the center. Clean air (75 % of total flow) is drawn from the center of the vortex chamber, through a tube to the sample cell with optical windows. The remaining 25 % of the flow carries the heavier dust particles away in a separate bypass tube. An EC155-system measured CO2 and H2O fluxes in two urban forest ecosystems in the megalopolis of Beijing, China. These sites present a challenge for EC measurements because of the generally poor air quality with high concentrations of suspended particulate. The closed-path EC system with vortex intake significantly reduced maintenance requirements by preserving optical signal strength and sample cell pressure within acceptable ranges for much longer periods. The system with vortex intake also maintained excellent high-frequency response. For example at the Badaling site, percentage system downtime due to plugged filters was reduced from 26 % with traditional in-line filters to 0 % with the prototype vortex intake. The use of vortex intake could extent the geographical applicability of the EC technique in ecology and allow investigators to acquire more accurate and continuous measurements of CO2 and H2O fluxes in a wider range of ecosystems.
Ma, J., Zha, T., Jia, X., Sargent, S., Burgon, R., Bourque, C. P.-A., Zhou, X., Liu, P., Bai, Y., and Wu, Y.: An innovative eddy-covariance system with vortex intake for measuring carbon dioxide and water fluxes of ecosystems, Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-280, in review, 2016.