Observations of the diurnal variation of nitrogen dioxide in the stratosphere

Observations of NO 2 from the limb infrared monitor of the stratosphere (LIMS) experiment in high‐latitude summer are presented. Appropriate selection of latitude and days during the month of May yields NO 2 observations obtained during the afternoon and evening at solar zenith angles ranging from about 35° to 110°. These data show that the NO 2 abundances in the stratosphere become strongly dependent on the solar zenith angle for angles exceeding about 80°. Model calculations and other observations suggest that from about 80° to 95° this dependence probably reflects variations in the propagation of the visible radiation that photodissociates NO 2 . The data obtained at zenith angles greater than about 95° provide clear evidence for the night decay of NO 2 to form N 2 O 5 , and the observed decay rate is shown to be consistent with present theory.