The first step to assess the accuracy of the cloud correction scheme in BIRA's NO2 retrieval is to generate synthetic data for various box cloud cases. The retrieval is then applied to the synthetic data. The analysis of the results will hopefully provide first insights in the performance of the cloud correction scheme depending on cloud type.

Cloud fractions [%]: 0,10,25,50,100

Cloud geometrical thickness 1km, bottom heights [km]: 1,3 (liquid water) 10 (ice)

Cloud optical thickness: 2,5,10,50

Surface albedos: 0, 0.1, 0.3, 0.8

solar zenith angles [degrees]: 30,60

viewing zenith angles [degrees]: 0,30,60

viewing azimth angles [degrees]: 0,90,180

NO2 profiles [pollution]: low, medium, high

continental aerosol: off, average

spectral bands: 400-500nm (0.2 nm resolution), 755-775nm (0.005 nm spectral resolution)

Total number of spectra and boxairmass-factors: 5x3x4x4x2x3x3x3x3x2 = 25920