Tropospheric ozone residual (TOR) is computed by subtracting the stratospheric column ozone from the total column ozone. The stratospheric column ozone is computed using the MLS limb measurements of ozone. The total column O₃ is measured by OMI, and the TOR is the difference between them.

The monthly mean maps of the TOR show pollution streaming from the U.S., Europe and China to the west in summer and pollution from biomass burning in the equatorial zone.