Measurements of NO, NO₂, and HNO₃ in the Stratosphere

Atmospheric models designed to predict the effect on the ozone budget of the injection of nitric oxide into the stratosphere by high-flying aircraft require a knowledge of the NO concentration in the unperturbed atmosphere. Moreover, a monitoring program will require a base line against which to measure the magnitude of any future stratospheric pollution. A number of measurements have recently been reported, not only on NO, but also on NO 2 , and HNO 3 which are interconverted by stratospheric photochemistry. All the methods but two employ "remote-sensing" optical absorption or emission techniques. Infrared solar absorption using long optical paths at twilight has proven to be very sensitive in detecting trace atmospheric constituents but quantitative interpretation appears to be very difficult. Chemiluminescence and direct "particle" sampling have provided insitu measurements.The spread in the reported values of mixing ratios is very large for NO 2 , appreciable, but smaller for NO, and smallest for HNO 3 . Insufficient data are available to assess how much of this spread is due to measurement errors and how much is due to natural variability in the mixing ratios. Intercomparisons of the measurements for different nitrogen compounds are made by consideration of the principal chemical reactions governing their relative concentrations. Discrepancies exist which should diminish as more accurate chemical rate data and synoptic stratospheric measurements become available.