Abstract
Nitrous oxide (N2O) is a powerful greenhouse gas and is the largest remaining anthropogenic source of stratospheric ozone-depleting substances as halocarbons return towards preindustrial levels. To verify the N2O emission inventory using inverse analysis, precise and reliable measurements are necessary. In this study, we compared the conventional gas chromatography with the microelectron capture detector method (GC-μECD, Agilent 7890A) with advanced off-axis integrated cavity output spectroscopy (OA-ICOS, Los Gatos, EP-30) for atmospheric N2O measurements at the Jeju Gosan Suwolbong Station (JGS, 126.16° E, 33.30° N, 71.47 m a.s.l) in South Korea. The measurement uncertainties from linearity, repeatability, and reproducibility derived from the two instruments were compared. The values derived from GC-μECD were 2.4 to 8.7 times greater than that of OA-ICOS in all factors at the station. Since these factors affect the measurement quality, the calibration strategy should be well-established to reduce the measurement uncertainty. These uncertainties resulted in biases from the measurement of atmospheric N2O. The parallel inter-comparison experiment was implemented at JGS for 22 months, and the difference in atmospheric N2O was 0.17 ± 0.9 ppb between the two instruments. The significant differences were observed in the nonlinear range of the GC-μECD. Finally, these differences resulted in the over/underestimation of N2O characteristics locally and seasonally. Overall, OA-ICOS has a more robust performance with a lower measurement uncertainty than GC-μECD. Based on this study, we also suggest a calibration strategy for both instruments to achieve precise N2O measurements.
Highlights
Nitrous oxide (N2 O) is a third powerful greenhouse gas with 0.202 W·m−2 radiative forcing expressed by global abundance changes relative to 1750, the preindustrial level [1] (The global warming potential of N2 O is 300 times more than that of carbon dioxide (CO2 ) over a 100 year time horizon due to its long lifetime [2,3]
GC-μECD was nonlinear in the target range, meaning that one-point calibration was not sufficient, while off-axis integrated cavity output spectroscopy (OA-ICOS) showed a linear response against the reference gases (Figure 2)
Even if a second-order polynomial was applied as the regression curve for GC-μECD, the residual was still more than the WMO/Global Atmosphere Watch Programme (GAW) compatibility goal in a certain range
Summary
Nitrous oxide (N2 O) is a third powerful greenhouse gas with 0.202 W·m−2 radiative forcing (in 2019) expressed by global abundance changes relative to 1750, the preindustrial level [1] (The global warming potential of N2 O is 300 times more than that of carbon dioxide (CO2 ) over a 100 year time horizon due to its long lifetime [2,3]. N2 O is involved in stratospheric ozone depletion [4], and its emissions weighted by ozone depletion potential currently exceed those of all other substances [5]. Atmospheric N2 O increased globally by 1 ± 0.3 ppb yr−1 from 2010 to 2018 [11]. This increment resulted from the increased use of inorganic fertilizers and manure [12,13,14], and those sources are all subject to significant uncertainty. The significant increasing trend in agricultural soil emissions from Southern Asia, which includes China and India, is mostly due to the rise in nitrogen fertilizers in these developing economies [13,14,15]
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