Enhancing sampling of dissolved N₂O in aquatic systems: Field-deployable automated gas bag collection system

Abstract

Measuring dissolved nitrous oxide (N₂O), a potent greenhouse gas and contributor to ozone depletion, is essential for understanding its aquatic dynamics and informing climate mitigation and emission estimates. Dissolved N₂O concentration measurements typically involve headspace equilibration of water samples in sealed containers, followed by gas chromatography analysis. This manual method is labor-intensive and often requires toxic preservatives. Alternatively, air-water exchangers coupled with laser analyzers provide high-precision continuous measurements but lack sample storage capabilities and require frequent relocation and setup to capture spatiotemporal variations. We developed an automated gas bag (AGB) collection system for collecting N₂O samples (AGB-N₂O) from discrete water samples, which could then be analyzed for concentration using laser analyzers. This method combines the field-friendly sample collection and storage of the manual method with the precision of exchangers and laser analyzers. Field experiments tested four setups of exchangers with varying internal volumes (2 L vs. 1 L) and water flow rates (small nozzle: 0.75 L min¯¹ vs. medium nozzle: 3 L min¯¹) at sites with low vs. high N₂O concentrations (13 nM vs. 95 nM). The 2-L exchanger with a medium nozzle achieved the fastest equilibration times of 2.25 and 0.08 min for high and low N₂O sites, respectively. The AGB-N₂O showed comparable results to the manual method for measuring dissolved N₂O concentrations (p > 0.05). However, the AGB-N₂O demonstrated significantly lower standard deviations, indicating higher precision and consistency. These findings demonstrate the suitability of the AGB-N₂O for diverse aquatic environments, offering reliable and efficient N₂O measurements.