Seasonal Variations of NO and 03 at Altitudes of 18.3 and 21.3 km

Abstract

Nitric oxide and ozone concentrations have been measured in situ from a high-altitude research aircraft based at the NASA Ames Research Center. Data which show the variations of NO and 03 with the time of year are presented for altitudes of 18.3 and 21.3 km. The extreme values of the observed NO concentrations at 21.3 km are 1.2?109 cm?3 in summer and 2?108 cm?3 in winter. At 18.3 km the extreme values are 1.6?109 cm?3 in summer and 1?108 cm?3 in winter. The smoothed NO seasonal data show a variation of about a factor of 2.5 at 21.3 km and a factor of 4 at 18.3 km. The ozone data show the generally expected magnitude and seasonal variation. We have used a photochemical model employing the measured ozone concentrations, the mean solar zenith angle, and seasonal HNO3 data reported by others to predict the seasonal NO variation at 20 km. The result is a summer-to-winter NO ratio of 2.5 which is in fair agreement with the observed ratios.