Q: Given a scientific passage and an answer, generate a question for the given answer.
Passage: Air quality is a measure of the pollutants in air. Poor air quality started to become a serious problem during the Industrial Revolution. After 1900, motor vehicles added greatly to the problem. The Clean Air Act of 1970 improved the quality of the air over the U. S. Answer: pollutants
A:
Air quality is a measure of what in the air?