The impact of gas‐surface reactions on mass spectrometric measurements of atomic nitrogen

Recently, atomic nitrogen has been measured in the upper thermosphere with a mass spectrometer carried on the Atmosphere Explorer satellites. Only a small fraction of N atoms are directly measured by the mass spectrometer, however. The majority appear as NO, formed within the ion source. Occasionally a relatively large NO 2 signal has also been observed, showing a strong dependence on the ion source surface temperature. Comparison of a numerical simulation of the reactions leading to NO 2 with data obtained in circular orbits on AE‐C provides insight into the pertinent chemical reactions. It demonstrates that the techniques used in open source neutral mass spectrometer operation—warmup and outgassing of the source before measurements—were successful in minimizing the effects of this contaminant.