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. The development of fast-response analysers for themeasurement of nitrous oxide (N2O) has resulted in excitingopportunities for new experimental techniques beyond commonly used staticchambers and gas chromatography (GC) analysis. For example, quantum cascadelaser (QCL) absorption spectrometers are now being used with eddy covariance(EC) or automated chambers. However, using a field-based QCL EC system toalso quantify N2O concentrations in gas samples taken from staticchambers has not yet been explored. Gas samples from static chambers areoften analysed by GC, a method that requires labour and time-consumingprocedures off-site. Here, we developed a novel field-based injectiontechnique that allowed the use of a single QCL for (1) micrometeorologicalEC and (2) immediate manual injection of headspace samples taken from staticchambers. To test this approach across a range of low to high N2Oconcentrations and fluxes, we applied ammonium nitrate (AN) at 0, 300, 600and 900 kg N ha−1 (AN0, AN300, AN600, AN900) toplots on a pasture soil. After analysis, calculated N2O fluxes from QCL(FN2O_QCL) were compared with fluxes determined by astandard method, i.e. laboratory-based GC (FN2O_GC). Subsequently, the comparability of QCL and GC data was tested usingorthogonal regression, Bland–Altman and bioequivalence statistics. For AN-treated plots, mean cumulative N2O emissions across the 7 dcampaign were 0.97 (AN300), 1.26 (AN600) and 2.00 kg N2O-N ha−1 (AN900) for FN2O_QCL and 0.99(AN300), 1.31 (AN600) and 2.03 kg N2O-N ha−1 (AN900) for FN2O_GC. These FN2O_QCL and FN2O_GC were highly correlated (r=0.996, n=81) based on orthogonal regression, in agreement following the Bland–Altman approach (i.e. within ±1.96 standard deviation of the meandifference) and shown to be for all intents and purposes the same (i.e.equivalent). The FN2O_QCL and FN2O_GC derived under near-zero flux conditions (AN0) were weaklycorrelated (r=0.306, n=27) and not found to agree or to beequivalent. This was likely caused by the calculation of small, but apparentpositive and negative, FN2O when in fact the actual flux was below thedetection limit of static chambers. Our study demonstrated (1) that thecapability of using one QCL to measure N2O at different scales,including manual injections, offers great potential to advance fieldmeasurements of N2O (and other greenhouse gases) in the future and (2) that suitable statistics have to be adopted when formally assessing theagreement and difference (not only the correlation) between two methods ofmeasurement.

A novel injection technique: using a field-based quantum cascade laser for the analysis of gas samples derived from static chambers