Slant column measurements of O3 and NO2 during the NDSC intercomparison of zenith-sky UV-visible spectrometers in June 1996
In June 1996, 16 UV-visible sensors from 11 institutes measured spectra of the zenith sky for more than 10 days. Spectra were analysed in real-time to determine slant column amounts of O3 and NO2. Spectra of Hg lamps and lasers were measured, and the amount of NO2 in a cell was determined by each spectrometer. Some spectra were re-analysed after obvious errors were found. Slant columns were compared in two ways: by examining regression analyses against comparison instruments over the whole range of solar zenith angles; and by taking fractional differences from a comparison instrument at solar zenith angles between 85° and 91°. Regression identified which pairs of instruments were most consistent, and so which could be used as universal comparison instruments. For O3, regression slopes for the whole campaign agreed within 5% for most instruments despite the use of different cross-sections and wavelength intervals, whereas similar agreement was only achieved for NO2 when the same cross-sections and wavelength intervals were used and only one half-day's data was analysed. Mean fractional differences in NO2 from a comparison instrument fall within ±7% (1-sigma) for most instruments, with standard deviations of the mean differences averaging 4.5%. Mean differences in O3 fall within ±2.5% (1- sigma) for most instruments, with standard deviations of the mean differences averaging 2%. Measurements of NO2 in the cell had similar agreement to measurements of NO2 in the atmosphere, but for some instruments measurements with cell and atmosphere relative to a comparison instrument disagreed by more than the error bars.
Authors: Roscoe, H. K., Johnston, P. V., Van Roozendael, M., Richter, A., Sarkissian, A., Roscoe, J., Preston, K. E., Lambert, J-C., Hermans, C., DeCuyper, W., Dzienus, S., Winterrath, T., Burrows, J., Goutail, F., Pommereau, J-P., D'Almeida, E., Hottier, J., Coureul, C., Didier, R., Pundt, I., Bartlett, L. M., McElroy, C. T., Kerr, J. E., Elokhov, A., Giovanelli, G., Ravegnani, F., Premuda, M., Kostadinov, I., Erle, F., Wagner, T., Pfeilsticker, K., Kenntner, M., Marquard, L. C., Gil, M., Puentedura, O., Yela, M., Arlander, D. W., Kastad Hoiskar, B. A., Tellefsen, C. W., Karlsen Tornkvist, K., Heese, B., Jones, R. L., Aliwell, S. R., Freshwater, R. A.