N2O soil fluxes as impacted by chambers and measurement technique

The exchange of greenhouse gases (GHG) between soil and the atmosphere is typically measured using the closed static chamber method at small scales (<0.1 ha). In this method, the gas flux is estimated based on the change in concentration over time within the chamber (non-steady state). For nitrous oxide fluxes (N 2 O), the traditional method is to sample the air from the chambers over elapsed time and analyze the concentration using a gas chromatograph (GC analysis). Over the past years, portable trace gas analyzers have become widely available, enabling in-situ measurements of N 2 O concentrations. Yet, as of 2025, GC analysis remains widely used. Chamber measurements may be either automated or manual and the air in the headspace can either circulate from the chamber to an analyzer unit and back (flow-through) or is confined inside the chamber (non-flow-through). In both cases the concentration of N 2 O increases over time (non-steady state) While the measurement principle is the same for non-steady measurements, there are differences in N 2 O flux measurements as affected by chamber type. Previously, different chamber designs and setups have been tested in chamber intercomparison campaigns under controlled conditions for other GHGs. The resulting flux estimates from different chambers varied substantially (Christiansen et al. 2011, Pihlatie et al. 2013, Pumpanen et al. 2004). In addition, field and semi-controlled environment tests revealed significant differences in N 2 O flux estimates between certain chamber setups using TGA and GC analysis, respectively (Kong 2025. Until now, there are only indications for why there are differences in N 2 O fluxes, partially because the experimental setup and resources determine the dimensions and type of chamber, which makes a comparison difficult. Furthermore, while there are commercial chambers available, most chambers are custom made and come in different dimension, shapes, and types. This further complicates the comparison. Despite the widespread use of portable trace gas analyzers, systematic testing of different chamber setups against a N 2 O reference flux or other chamber setups has not been sufficiently conducted. To our knowledge, there is only one unpublished dataset of N 2 O chamber intercomparison (Pihlatie et al., unpublished data ). In this study, we aim to revisit the dataset and investigate these differences in flux estimates further, comparing various setups against a known reference flux in a controlled experiment. The objective is to identify error sources and provide general uncertainty estimates for chamber measurements, including data processing and flux calculation, which is particularly important for measurements based on GC analysis. This will facilitate the assessment of systematic errors in existing datasets globally. Recommendations for chamber setup design will be updated as necessary. We will present first results and give an outlook on future activities.