Am. Lee et al., IMPROVEMENTS TO THE ACCURACY OF MEASUREMENTS OF NO2 BY ZENITH-SKY VISIBLE SPECTROMETERS, Journal of quantitative spectroscopy & radiative transfer, 52(5), 1994, pp. 649-657
Visible spectra of the zenith-sky were recorded at Faraday in Antarcti
ca during 1990. Line-of-sight NO2 amounts were deduced by fitting labo
ratory cross-sections to the spectra. A new procedure was used to dete
rmine the offset to the zero of the measurement from the measurement s
eries itself. This offset includes the effect of the reference spectru
m-a single reference was used for the whole data set-plus any instrume
ntal or analytic artefacts. It is important to determine this offset t
o the zero because it affects the absolute calibration of the zero of
the vertical amount of NO2. In the new procedure, offsets were determi
ned from fits to plots of the measured line-of-sight NO2 vs calculated
air-mass factors, whose curvature had been precomputed from model pre
dictions rather than the straight-line fits of Langley plots. The resu
lting vertical NO2 amounts were significantly lower than those deduced
using a more subjective determination of offset, particularly in the
early spring when denitrification might be expected.