A reassessment of the global isotopic budget of atmospheric nitrous oxide

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 firn or ice and modern air. This build-up of isotopically light, anthropogenic nitrous oxide can be thought of as an N2O '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 N2O isotopic signature as well as provide insight into the pathways of the anthropogenic sources.