Great idea. They could also be used to find the source of air pollutants and chemical leaks. The drones open a new way to quickly search an area for items of interest. It would be a short step to integrate coordinated search coordinates to the drones and have them work together to map the levels of any substance they could detect.
I agree, this was one of the more compelling uses. Imagine being able to deploy these at accidents involving spills, and for a lot of other recovery situations where now people are put into harm's way.
One of the interesting new things that these drones could do in addition to what the current air pollution equipment does , is that , they can travel and trace the source from where the pollutants are being added to the air , say zeroing onto a factory exhaust , thereby pin pointing the cause and extent of the pollution. Such thing would not be possible by the current stationary monitoring equipment