The majority of the photochemical processes involving the trace gas species that interest us take place in the troposphere. Our focus, therefore, is directed towards the vertical column of air above the ground pixel that stretches from the surface to the top of the troposphere at an altitude of ~8-15 km. This is known as the tropospheric vertical column VC_trop.

The task of the remote sensing of NO₂ is to measure the quantity of NO₂ in the VC_trop.

Fig 3.4.1.1.1: The tropospheric vertical column.

Image: AT2-ELS

Note that in most of the diagrams in this section the thickness of the troposphere (~15 km) and that of the stratosphere (~50 km) are not shown to scale.