Ground based observations of stratospheric nitrogen dioxide

Ground based measurements of stratospheric NO 2 , using four different established methods based on twilight sky observations in the spectral region 437.0–451.0 nm have been made at two locations: Primrose Lake (54.78°N, 110.05°W) and at Priddis (50.86°N, 114.29°W), Alberta, Canada, during March and April 1979. The four methods differ from one another on the basis of: (a) whether or not stratospheric ozone is taken into account, (b) whether a continuous NO 2 absorption spectrum or just the absorption at a few discrete wavelengths is used for analysis, and (c) the assumed altitude distribution of NO 2 concentration. Two different independently developed altitude distribution models are employed in obtaining the NO 2 vertical column abundance and its effective altitude from a set of slant column abundances, measured in the twilight sky at different solar zenith angles in the range 85–96°. A comparison shows that the use of one or the other of these two models alone could introduce a difference of as much as 30% in the derived vertical column abundance.