alt Hacker NewsI remember an interview with the producthead of Google Earth (the desktop client), she said when photographing all the streets, the cars also checked for air pollution: She mentioned a capital in Europe, where the amount of particles under certain sizes differed by 10x from one crossing to the next.
The measurement may very well be accurate but statements like that should set off massive red flags and not be taken at face value. A factor of ten difference for something that just kinda diffuses through the air doesn't "just exist". You don't get gradients like that "naturally" for the most part. It's the result of something. Maybe there's a source something is upwind of and something else is downwind of. Maybe there's conditions causing it to concentrate. Or it varies 10x day to day, but on an average basis it equals out. Etc. Etc.