Improvements to the accuracy of measurements of NO2 by zenith-sky visible spectrometers II: errors in zero using a more complete chemical model

Using a flexible chemical box model with full heterogeneous chemistry, inte rcepts of chemically modified Langley plots have been computed for the 5 ye ars of zenith-sky NO2 data from Faraday in Antarctica (65 degreesS). By usi ng these intercepts as the effective amount in the reference spectrum. drif ts in zero of total vertical NO2 were much reduced. The error in zero of to tal NO2 is +/- 0.03 x 10(15) melee cm(-2) from one year to another. This er ror is small enough to determine trends in midsummer and any variability in denoxification between midwinters. The technique also suggests a more sens itive method for determining N2O5 from zenith-sky NO2 data. (C) 2000 Elsevi er Science Ltd. All rights reserved.