SustainableDavid:  Why? The only thing in common is Ozone--O3. Otherwise, Stratospheric O3 ("S O3") is beneficial, ground level O3 ("GL O3") is hazardous and toxic. S O3 is 1000s of feet up in the atmosphere; GL O3 is usually no more than 1000 feet. S O3 is a natural feature; GL O3 is human-caused pollution. One is the unwanted destruction of O3; the other is the unwanted production of O3. One is caused by the gradual migration of toxic chemicals into the stratosphere, where they react over and over and over to dissociate O3 for years; the other happens in a few hours and can happen every day. One is global; the other occurs in metropolitan areas with industries and traffic congestion.

Completely different characteristics: extent of coverage, constituents, concerned public, effects, causes, solutions, priorities....
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