Given a scientific passage and an answer, generate a question for the given answer.
Q: Passage: Poor air quality started to become a serious problem after the Industrial Revolution. The machines in factories burned coal. This released a lot of pollutants into the air. After 1900, motor vehicles became common. Cars and trucks burn gasoline, which adds greatly to air pollution. Answer: industrial revolution
A:
During what time period did poor air quality become a problem?