Novel Method for Nitrogen Isotopic Analysis of Soil-Emitted Nitric Oxide.

The global inventory of NO x (NO x = NO + NO2) emissions is poorly constrained, with a large portion of the uncertainty attributed to soil NO emissions that result from soil abiotic and microbial processes. While natural abundance stable N isotopes (?15N) in various soil N-containing compounds have proven to be a robust tracer of soil N cycling, soil ?15N-NO is rarely quantified due to the measurement difficulties. Here, we present a new method that collects soil-emitted NO through NO conversion to NO2 in excess ozone (O3) and subsequent NO2 collection in a 20% triethanolamine (TEA) solution as nitrite and nitrate for ?15N analysis using the denitrifier method. The precision and accuracy of the method were quantified through repeated collection of an analytical NO tank and intercalibration with a modified EPA NO x collection method. The results show that the efficiency of NO conversion to NO2 and subsequent NO2 collection in the TEA solution is >98% under a variety of controlled conditions. The method precision (1?) and accuracy across the entire analytical procedure are ±1.1‰. We report the first analyses of soil ?15N-NO (-59.8‰ to -23.4‰) from wetting-induced NO pulses at both laboratory and field scales that have important implications for understanding soil NO dynamics. [ABSTRACT FROM AUTHOR]