A reassessment of the global isotopic budget of atmospheric nitrous oxide

Abstract

Abstract. A simple box model is developed which accounts for the natural and anthropogenic sources and sinks of tropospheric nitrous oxide. Stable isotopic terms are included as well to investigate what additional insight they might provide concerning the overall picture of the global nitrous oxide budget. It is seen that fractionation associated with ultraviolet photolysis in the stratosphere plays a key role in balancing the isotopic budget. It is also noted that increased production due to human influence should have a unique isotopic signature which should provide observable differences between preindustrial air trapped in polar tim or ice and modem air. This build-up of isotopically light, anthropogenic nitrous oxide can be thought of as an N20 "Suess effect" and should be observable in time series measurements of clean baseline atmospheric samples. High-precision records of such changes could lead to a better estimate of the preindustrial N20 isotopic signature as well as provide insight into the pathways of the anthropogenic sources.

Isotopic signatures of N2O produced by ammonia-oxidizing archaea from soils

“…The end-member mixing model was not applicable to the CS culture because of the partial oxidation of ammonia and hence the 15 N bulk -N 2 O produced by strain CS did not reflect the isotopic shifts of NH 4 þ . The ranges of d 15 N bulk -N 2 O from soil AOA were similar to those (-10 to -50%) from agricultural soils and forest soils (Kim and Craig, 1993;Rahn and Wahlen, 2000;Pérez et al, 2001;Rock et al, 2007). Previous studies found that the d 15 N bulk -N 2 O values of marine AOB (Nitrosomonas marina C-113) were about -10% with 20% O 2 concentration (Frame and Casciotti, 2010), whereas the d 15 N bulk -N 2 O values of N. europaea (ATCC 19718) in ammonia-oxidizing and nitrite-reducing conditions were -46.5% and -34.0%, respectively (Sutka et al, 2003(Sutka et al, , 2006.…”

Online technique for isotope and mixing ratios of CH<sub>4</sub>, N<sub>2</sub>O, Xe and mixing ratios of organic trace gases on a single ice core sample

“…4.3). The amount of air trapped within the ice sample is also used to calculate the total air content of the ice (Raynaud and Lebel, 1979). To this end, the bulk air leaving the AirTrap at −78 • C is re-collected on the air volume trap at −196 • C (SST tubing,8 cm,o.d.…”

“…To identify melt layers from a reduced air content caused by melting, the "background air content" of unaffected bubble ice has to be established, which is primarily a function of the altitude (Raynaud and Lebel, 1979). The third principle uses the fact that some gases are more water-soluble than other gases, producing characteristic deviations in the mixing ratios of otherwise temporally fairly constant atmospheric gas species.…”

“…Typically, the combined uncertainty of air content measurements is 1 % (Raynaud and Lebel, 1979). To identify melt layers from a reduced air content caused by melting, the "background air content" of unaffected bubble ice has to be established, which is primarily a function of the altitude (Raynaud and Lebel, 1979).…”

“…to distinguish among sources and sink processes (Sowers et al, 2003;Ferretti et al, 2005;Bock et al, 2010b;Schmitt et al, 2012). For example, N 2 O emitted from the ocean is enriched in the heavy isotopologues for both nitrogen and oxygen compared to emissions from terrestrial ecosystems (Rahn and Wahlen, 2000); likewise CH 4 emitted from biomass burning is enriched in the heavy carbon isotope 13 C compared to microbial CH 4 . On the other hand, the wide natural variability of a particular source signature often leads to overlaps among sources, and source signatures may change through time .…”