Reference NO2 calibration system for ground‐based intercomparisons during NASA's GTE/CITE 2 mission

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Abstract
An NO2 calibration system, based upon a permeation device and a two‐stage dynamic dilution system, was designed, constructed, and characterized at the National Bureau of Standards. In this system, calibrant flow entering the second stage was controlled without contacting a metal flow controller, and permeation oven temperature and flow were continuously maintained, even during transport. The system performance and the permeation emission rate were characterized by extensive laboratory tests based on gravimetry, chemiluminescence detection, and tunable diode laser absorption spectroscopy. This system was capable of accurately delivering known NO2 concentrations in the ppbv and sub‐ppbv concentration range with a total uncertainty of approximately 10%. Upon completion of these tests the calibration system was placed on board NASA's research aircraft at both the Wallops Island and Ames research facilities. There it was employed as the reference standard in NASA's Global Tropospheric Experiment/Chemical Instrumentation Test and Evaluation 2 mission in August 1986, as discussed in a companion paper (Gregory et al., this issue).