The observation of chemiluminescent NiO* emissions in the laboratory and in the night airglow

• Main Authors: W. F. J. Evans, R. L. Gattinger, A. L. Broadfoot, E. J. Llewellyn
• Format: Article
• Language: English
• Published: Copernicus Publications 2011-09-01
• Series: Atmospheric Chemistry and Physics
• Online Access: http://www.atmos-chem-phys.net/11/9595/2011/acp-11-9595-2011.pdf

The recent finding of an orange spectral feature in OSIRIS/Odin spectra of the night airglow near 87 km has raised interest in the origin of the emission. The feature was positively identified as the chemiluminescent FeO* emission where the iron is of meteoric origin. Since the meteorite source of atomic metals in the mesosphere contains both iron and nickel, with Ni being typically 6 % of Fe, it is expected that faint emissions involving Ni should also be present in the night airglow. The present study summarizes the laboratory observations of chemiluminescent NiO* emissions and includes a search for the NiO* signature in the night airglow. A very faint previously unidentified "continuum" extending longwave of 440 nm has been detected in the night airglow spectra obtained with two space-borne limb viewing instruments. Through a comparison with laboratory spectra this continuum is identified as arising from the NiO* emission. The altitude profile of the new airglow emission has also been measured. The similarity of the altitude profiles of the FeO* and NiO* emissions also suggests the emission is NiO as both can originate from reaction of the metal atoms with mesospheric ozone. The observed NiO* to FeO* ratio exhibits considerable variability; possible causes of this observed variation are briefly discussed.