Since what year has PM10 pollutants been regulated under the Clean Air Act?

The regulation of PM10 pollutants under the Clean Air Act began in 1970, coinciding with the significant amendments to the Act that established the National Ambient Air Quality Standards (NAAQS). This year marked a pivotal moment in environmental policy, as it set regulatory measures in place for various pollutants, including particulate matter with a diameter of 10 micrometers or smaller (PM10).

The Clean Air Act was first enacted in 1963, but it was the 1970 amendments that expanded its scope significantly, laying the groundwork for a comprehensive framework to address air pollution. The 1990 amendments, while important for enhancing regulatory measures and introducing additional pollutants, did not initiate the regulation of PM10, as that was already established in the earlier amendments. The remaining years—1980 and 1963—are prior to the introduction of PM10 regulations, making them incorrect choices. Therefore, the correct choice reflects the foundational year when these specific air quality standards were set into motion.