Observation of NO2 diurnal variation in the stratosphere

Spectrometric measurements of nitrogen dioxide by the observation of the sunlight absorption in the visible range, from a balloon executing large vertical excursions, were performed along a complete day on September 1979 at 43°N, 00°W. The instrument and the data processing method developed allow a detection limit of NO2 along the line of sight of 4×1015 mol cm −2. The results show in the lower stratosphere an NO2 diurnal variation with a maximum around noon. Above 22 km, the vertical column density varies from 2.4 ± 0.7×1015 mol cm −2 at 06:15 to 10.0 ± 2.8×1015 mol cm −2 at 11:20 and 6.4 ± 1.4×1015 mol cm−2 at 17:00. At noon, the mean concentration between 22 and 33.5 km is 8.7 ± 3.2×109 mol cm −3 which corresponds to a mixing ratio of 13.1 ± 4.8 ppbv. By comparison with a solar spectrum obtained at 33 km, ground observations made the day before the flight around 13:00 allow a direct measurement of the total atmospheric NO2 column density : 24 ± 3×1015 mol cm−2.