Applicability of an eddy covariance system based on a close-path quantum cascade laser spectrometer for measuring nitrous oxide fluxes from subtropical vegetable fields

Abstract

AbstractThe soil of subtropical vegetable fields is an important source of the atmospheric greenhouse gas nitrous oxide (N2O). In a field study in subtropical China, the authors used an eddy covariance (EC) system based on a close-path quantum cascade laser (QCL) spectrometer to measure N2O fluxes from a vegetable field. During the experimental period from 9 October 2014 to 18 February 2015, the observed half-hourly N2O fluxes ranged from −10.7 to 1077.4 μg N m−2 h−1, with a mean value of 99.3 μg N m−2 h−1. The detection limit (95% confidence level) of the EC system for half-hourly fluxes was estimated at 18.5 μg N m−2 h−1, i.e. smaller than 97.5% of all measured fluxes, and within the range of the lower limit of reported N2O emissions from subtropical vegetable fields. The random uncertainties in the half-hourly fluxes were estimated at 60% on average, of which 62% was due to stochastic variations caused by turbulence and 38% by instrumental noise. The flux systematic uncertainties were estimated at −18%...