Field Performance Verification of Carbon Dioxide, Water, and Nitrous Oxide Closed-Path Eddy Covariance Systems with Vortex Intakes

Abstract:

Closed-path eddy covariance systems measure the flux of greenhouse gasses such as carbon dioxide, water vapor, and nitrous oxide. The challenge is to make accurate field measurements at sites around the world, even in extreme environmental conditions. Sites with dirty air present a particular challenge. Gas concentration measurements may be degraded as dust or debris is deposited on the optical windows in the sample cell. The traditional solution has been to add an in-line filter upstream of the sample cell to keep the windows clean. However, these filters clog over time and must be changed periodically. An in-line filter also acts as a mixing volume and in some cases limits the frequency response of the analyzer. A novel eddy-covariance system that includes a vortex air cleaner at the inlet has been developed and field tested. This new system eliminates the need for a traditional in-line filter to keep the sample cell windows clean. The new system reduces system maintenance and down time. Eddy covariance systems with the vortex intake were tested at several sites ranging from sites with extremely dirty urban air to sites with relatively clean mountain air, and in agricultural areas. These flux systems were monitoring either CO₂ and H₂O, or N₂O. Results show that the closed-path eddy covariance systems with a vortex intake perform very well and require lower maintenance compared to similar systems with in-line filters.