Analytical Sciences, Talk
Laser based N2O isotopomer analysis bridges the gap between pure culture studies and field applications
Ellen Gute1, Eliza Harris1, Benjamin Wolf1, Stephan Henne1, Lukas Emmenegger1, Joachim Mohn1
1EMPA Dübendorf
Nitrous oxide (N2O) is a potent greenhouse gas and the strongest ozone-destroying substance emitted this century. Atmospheric N2O concentrations have been rising at a rate of 0.2-0.3% per year over the past decades due to anthropogenic emissions, primarily arising from enhanced microbial production in fertilized agricultural soils. N2O sources are linked to different microbial processes, therefore sources are disperse and highly variable, complicating the development of effective mitigation strategies. Isotopic measurements have great potential to unravel spatial and temporal variations in sources, sinks and chemistry of N2O. Recent developments in quantum cascade laser spectroscopy [1] allow both the intermolecular distribution of 15N substitutions (‘site preference’; 15N14N16O versus 14N15N16O) and the oxygen isotopic composition (δ18O) of N2O to be measured with a precision of
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 wastewater, soil and aqueous solution [e.g. 3]. Specific pathways were favored 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.

Real-time analysis of N2O isotopic composition in ambient air is feasible by combining high precision laser spectroscopy with automated preconcentration [4]. In the first field campaign measuring real-time N2O isotopic composition, we monitored an intensively managed grassland in central Switzerland for three months. The responses of the N2O isotopic composition of soil-emitted N2O were analyzed with respect to management events and weather influences [5]. In a follow-up project we intend to 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 be of upmost importance for developing targeted mitigation options.
[1] H. Wächter, J. Mohn, B. Tuzson, L. Emmenegger, M. W. Sigrist, Opt. Express 2008, 16, 9239-9244.
[2] E. Harris, D. D. Nelson, W. Olszewski, M. Zahniser, K. E. Potter, B. J. McManus, A. Whitehill, R. G. Prinn, S. Ono, Anal. Chem. 2014, 86, 1726-1734.
[3] P. Wunderlin, M. F. Lehmann, H. Siegrist, B. Tuzson, A. Joss, L. Emmenegger, J. Mohn, Environ. Sci. Technol. 2013, 47, 1339-1348.
[4] J. Mohn, B. Tuzson, A. Manninen, N. Yoshida, S. Toyoda, W. A. Brand, L. Emmenegger, Atmos. Meas. Tech., 2012, 5, 1601-1609.
[5] B. Wolf, B. Tuzson, L. Merbold, C. Decock, L. Emmenegger, J. Mohn, EGU, 2014, Vienna.