A Calibration System for Evaluating N2O Soil Flux Chamber Performance

Abstract:

Nitrous oxide (N₂O) is an extremely potent greenhouse gas that is produced naturally in the soil environment during both nitrification and denitrification. Chamber based techniques – adapted from other greenhouse gas research fields – have been used for many years to study soil N₂O emissions. These chambers can provide estimates of gaseous fluxes, but some techniques have been shown to produce systematic bias. These biases have been well studied for more abundant greenhouse gases such as carbon dioxide, but a detailed understanding is lacking for N₂O due to the technical challenges associated with N₂O determination (e.g. low signal-to-noise ratio in gas chromatography (GC) measurements). Recent advances in laser technology enable N₂O measurements to be made in real time with high accuracy and precision, allowing for quantification of potential systematic biases introduced by chamber systems. Here, we present a laboratory-based system consisting of a large gas reservoir with a perforated lid and variable-depth sand column that produces stable N₂O fluxes, which can be used to benchmark chamber performance. The theory and development of the system is outlined, along with three-dimensional model results that assess the system’s performance and potential limitations (e.g. proximity limitations for multiple chambers, effect of large chambers on the calibration system dynamics). Preliminary results from the InGOS multi-institution chamber benchmarking study are also presented, which will focus on chamber performance across a wide range of N₂O fluxes and cross-chamber comparisons demonstrating the significance of measurement protocol and chamber design in error elimination.