Ground-based measurements of atmospheric NO₂ by differential optical absorption

Abstract

Nitrogen dioxide is important to stratospheric ozone chemistry¹. The few observations of vertical distribution of the gas are reviewed elsewhere². Most available data relate to ground-based measurements of the total amount in the vertical column. Such observations are ideally made from a high altitude site to avoid local tropospheric sources. Noxon³ observed a mean value of 5 × 10¹⁵ molecules cm^–2 from Fritz Peak Observatory. Pommereau and Hauchecorne⁴ obtained much higher values, of a few ×10¹⁷ molecules cm^–2, at Haute-Provence Observatory. Noxon et al. have reported latitudinal gradients^5,6 and response to stratospheric warmings⁷, reporting stratospheric column values in the range 1–5 × 10¹⁵ molecules cm^–2. During the past year, several series of observations have been made from a low altitude rural site in the UK. Values obtained for the vertical column were in the range 0.8–5.6 × 10¹⁶ molecules cm^–2. In view of the tropospheric contribution expected at this site⁸, these values represent an upper limit to the stratospheric NO₂ column and we show here that the values reported by Pommereau and Hauchecorne were anomalously high.