Understanding N2O sources and sinks with laser based isotopic analysis

Abstract:

Nitrous oxide (N₂O) is a potent greenhouse gas and the strongest stratospheric ozone-destroying substance released in the 21^st century. Main N₂O emissions are linked to different microbial pathways, therefore sources are disperse and highly variable, complicating their interpretation. Isotopic measurements have great potential to distinguish between individual source and sink processes. Developments in laser spectroscopy allow both the intramolecular distribution of ¹⁵N substitutions (¹⁵N¹⁴N¹⁶O versus ¹⁴N¹⁵N¹⁶O) and the oxygen isotopic composition of N₂O to be measured in real-time, at high precision and in excellent compatibility to IRMS [1].

In a number of laboratory and pilot plant studies we investigated the isotopic signature of distinct microbial and abiotic N₂O production and consumption pathways in soil and aqueous solution [e.g. 2-4]. Specific pathways were favoured by selection of the nitrogen substrates and process conditions and their isotopic signatures identified by real-time laser spectroscopic analysis. Results from our laboratory studies are in accordance with pure culture experiments and can therefore be applied to other ecosystems.

High precision isotopic analysis at ambient N₂O concentration is feasible by combining laser spectroscopy with automated preconcentration. Field deployment was demonstrated by real-time monitoring of the isotopic composition of N₂O emissions above an intensively managed grassland in central Switzerland. The responses of the N₂O isotopic signatures were analysed with respect to management events and climatic conditions [5]. In a follow-up project we combine real-time N₂O isotopic analysis at a tall tower in central Switzerland with atmospheric transport simulations and a biogeochemical model of surface fluxes of N₂O isotopomers. The working hypothesis is that this approach will allow us to quantify regional N₂O sources, identify emission hot spots, and constrain source processes, which will significantly advance our understanding of this important greenhouse gas.

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[5] B. Wolf et al. Biogeosci. (2015) 12, 2517.