Daily Column Ozone

The algorithm for calculating the column ozone of the atmosphere is based on the work of Gao et al. (2001), which uses the direct-beam irradiance for the retrieval. Given spectral measurements of UV-B, the total column ozone Q in Dobson units is calculated as:

where

Px Rayleigh scattering optical depth at wavelength A;

ma air mass corresponding to the SZA (#) at the time when the measurement is taken;

P observed station atmospheric pressure;

P0 mean sea level atmospheric pressure;

ax ozone absorption coefficient (base e) at wavelength A;

extraterrestrial voltage intercept at zero air mass at wavelength A;

Vi direct normal voltage after cosine and dark current bias corrections at wavelength A;

/u ratio of the actual and the vertical paths of solar radiation through the ozone layer;

R average earth radius (6,371.229 km);

z height of the station above mean sea level;

h height of ozone layer above mean sea level at station location (20 km is assumed);

d solar zenith angle.

Total column ozone is computed using those 3-min average measurements when the irradiance at 311 nm is greater than 0.002,5 Wm-2nm-1 and the condition d > 70° holds. Daily total column ozone is then determined by averaging these 3-min results if there are at least five of such 3-min averages.

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