Radiometer based on the principle of Zeeman modulation designed for the measurement of NO in the atmosphere.

The principles, construction, and operation of a novel gas correlation spectrometer employing the Zeeman effect to perform selective modulation are described. The retrieval of column amounts of atmospheric nitric oxide (NO) is discussed. The sun is used as an IR source, and the radiation is modulated by the splitting of absorption lines in a sample of NO gas which is positioned in a variable longitudinal field. A sample of the results obtained at a high altitude observatory is presented. The diurnal variation in the observed NO column is consistent with photochemical predictions. Unexpected shorter term variabilities which are observed may be dynamic effects but are more likely to be instrumental artifacts. The instrument is insensitive to tropospheric NO, making it potentially useful for long term monitoring from the ground of NO in the stratosphere and mesosphere.