How satellite instruments track air pollution

This image shows a huge smoke plume (in white) mixed with smog hanging over Indonesia. Colours represent variations in ozone amounts (expressed in Dobson units).

Smog is composed of low-level tropospheric ozone and fine particles usually produced by industries and transports.

This blanket of pollution was caused by the many fires that spread over Indonesian islands in the second half of 1997.

Question: What do satellites have to do with air pollution ?