A Long-Term Field Trial of a Lower-powered Eddy Covariance System for Measuring Nitrous Oxide Fluxes

A Long-Term Field Trial of a Lower-powered Eddy Covariance System for Measuring Nitrous Oxide Fluxes

Eddy covariance measurements of N₂O fluxes are suitable for capturing the spatial and temporal heterogeneity of N₂O emissions. Available closed-path systems for use with EC have multipass absorption cells that necessitate high flow rates, and thus high power usage.  Filter requirements lower the response time, increase frequency losses, and increase maintenance requirements. This field trial tested the performance of a closed-path EC system that improves on traditional instrumentation for N₂O flux measurements.  The new system consisted of a Campbell Scientific TGA200A configured to measure both N₂O and CO₂, and features a relatively small sample cell that allowed for the use of a lower-powered pump (~230 W).    A new vortex intake removed particulates from the sample air stream with no filter to clog and no additional mixing volume that could degrade frequency response.  This intake also dried the air to supersede spectroscopic or WPL corrections.  This EC system was collocated with a traditional analyzer (Campbell Scientific TGA100A) to compare N₂O and CO₂ flux measurements for a year (May 2015 to May 2016) in a fertilized cornfield in Southern Ontario, Canada.  A fast-response closed-path Campbell Scientific CPEC200 also measured CO₂ and H₂O fluxes at the same location.  Both TGA systems were rugged to the environmental conditions, as both operated through all weather conditions in the summer (air temperatures > 30^oC) and winter (< -20^oC).  The new system rarely required maintenance, and data losses over the year were minimal. Preliminary results showed that spectral losses for N₂O were small for both systems.  Spectral corrections for CO₂ were also small and comparable to those of the CPEC200 system. Values of the N₂O fluxes were similar between the two systems; CO₂ fluxes from both TGA systems correlated well to those measured by the CPEC200 (r² > 0.9).