Two methods are used to remove the values measured for stratospheric NO₂ from the values measured for the total slant column of NO₂ to leave the tropospheric slant column for NO₂. These are considered in detail in the following sections:

• The use of a reference sector measured during an orbit over a section of the Pacific with very low tropospheric NO₂ values.
• The use of the SCIAMACHY limb scanning mode to measure stratospheric NO₂ concentrations directly.