When did regulation of PM2.5 pollutants begin?

The regulation of PM2.5 pollutants began in 1997, which is when the U.S. Environmental Protection Agency (EPA) issued the final rule to designate PM2.5 as a criteria pollutant under the Clean Air Act. This regulation established the National Ambient Air Quality Standards (NAAQS) specifically for fine particulate matter (PM2.5), which includes particles that are 2.5 micrometers in diameter or smaller. The importance of regulating PM2.5 stems from its significant impact on human health, as these small particles can penetrate deep into the lungs and even enter the bloodstream, leading to respiratory and cardiovascular issues.

Earlier dates, including 1980, 1990, and 1970, refer to different milestones or regulations in air quality management or the establishment of the EPA itself, but they do not pertain specifically to the introduction of PM2.5 regulation. Thus, 1997 is the key year when the focus shifted explicitly to managing this type of air pollutant, marking a significant step in environmental regulation aimed at protecting public health and the environment.