Direct Measurements of Stable Isotope Ratios in Nitrous Oxide in Air

 

Research Staff: Hansjürg Jost, James R. Podolske

Nitrous oxide (N2O) is increasing at a rate of about 0.3% per year in the atmosphere. It is an important greenhouse gas and its decay products react with the ozone layer, potentially influencing the future of life on this planet. There is still a large uncertainty in the ground level sources of N2O, which are believed to be from biological activity. Isotopic ratios can be used to characterize such sources and help reduce the uncertainties in the source budget and add to our understanding of signatures of life.

Only limited isotopic data of the main sources (tropical soils, temperate soils) is currently available and almost no isotope ratio data on seasonal and annual variations and changes in anthropogenic sources exist. An instrument with long term, continuous determination of isotope ratios will contribute tremendously to a better characterization of N2O sources and understanding of the underlying (physiological) processes.

We are currently building a prototype instrument to perform in-situ, non-destructive measurements of isotope ratios of trace gases in ambient air in real time to allow continuous monitoring. It employs a tunable diode laser and state of the art optical cavities. Our cavities are 0.9 m long and with mirror reflectivities of greater than 99.99% have an effective path length of more than 9 km. This long optical path allows us to accurately measure the weak spectroscopic features created by the different, rare isotopes of a trace gas.

We plan to characterize the long term sensitivity of the prototype and expect that continued development of this technology will lead to a field deployable instrument.

 

Collaborators: Todd B. Sauke, SSX

Point of Contact: Hansjürg Jost, 650/604-0697, hjost@mail.arc.nasa.gov