For the measurement of atmospheric NO2 vertical column density (VCD). Kitt Peak Solar Flux Atlascan be substituted as an extraterrestrial solar radiation. Compared with differential analysis method, theTaylor expansion of integrated transfer equation underestimates the VCD. This underestimation is as largeas 35% when the amount of NO2 is 1×1017 cm-2 and observation is conducted with an air mass factor of10. Even when the VCD is 2×1016 cm-2 and the air mass factor is 4, the relative error of the retrieved VCDis still no less than 3%. If the observation is restricted under the small air mass factor condition (≤4), withKitt Peak Solar spectrum as an extraterrestrial solar radiation, only an atmospheric layer of 2 km thick fromground can be studied, which will make the absorption too weak to be detected by normal instruments.The VCD in winter Tokyo area was observed and analyzed by differential method. which shows a goodprecision even when the absorption is as low as 3%. The largest average VCD was about 1.3×1017cm-2.and the lowest was about 1.3×1016 cm-2. The trend of its variation was almost the same as the ground levelobservation by Saltzman reagent method.
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