To what extent are environmental regulations responsible for the fact that the air in our cities is much cleaner today than it was 40 years ago? Some evidence from the United States suggests that other forces may be primarily responsible.
Proponents of an aggressive approach to environmental regulation in America often point to the Clean Air Act as a signature achievement, which they credit for the improvement in air pollution levels in America’s cities. Air quality in Canadian cities has similarly improved during this time period.
The data in this graphic, however, suggests that air pollution levels had already been dropping quickly for almost a decade before the Clean Air Act was passed. The trend did not accelerate noticeably in the following years. The improvement in air quality is a hugely positive development (of which many people are unaware). This data suggests, however, that those who attribute this progress in the United States to the Clean Air Act may well be mistaken.