The total NO₂ slant column density of a species for a ground pixel, SCD_total, is determined using the DOAS method applied to nadir mode measurements.

Fig 3.4.1.5.1: The total slant column in the stratosphere and the troposphere.

Image: AT2-ELS

The DOAS procedure used here takes the raw spectroscopic data and

• compensates for the imperfections of the solar irradiance;
• removes spurious effects arising from scattering and inelastic absorption processes in the atmosphere and at the surface;
• calculates the concentration of the species in the slant column (that is, the SCD_total) of the species by fitting reference spectra to the measured spectrum.