Question

tall smokestacks were built due to the theory \dilution is the solution to pollution.\ it caused local air quality to improve, but what problems did it cause?
improved global air quality
decreased air quality downwind

Explanation:

Tall smokestacks disperse pollutants higher in the atmosphere, which then drift downwind and accumulate in areas farther from the source, worsening air quality in those downwind regions rather than improving global air quality.

Answer:

Decreased air quality downwind