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Particulate matter (PM) air pollution refers to microscopic airborne particles made up of dust, dirt, soot, smoke, sulfates, nitrates, and liquid droplets. PM can vary in size but according to the Environmental Protection Agency (EPA), particles less than 2.5 micrometers in diameter (PM2.5) are believed to pose the greatest risks to human health. Due to the small size of PM2.5, it can travel longer distances and has a longer life than coarse particulate matter.

Because of its small size and capacity to remain suspended in the air, PM2.5 can become deeply embedded in the lungs, causing adverse health effects. EPA states:

"Health studies have shown a significant association between exposure to fine particles and premature death. Other important effects include aggravation of respiratory and cardiovascular disease (as indicated by increased hospital admissions, emergency room visits, absences from school or work, and restricted activity days), lung disease, decreased lung function, asthma attacks, and certain cardiovascular problems such as heart attacks and irregular heart beat. Individuals particularly sensitive to fine-particle exposure include older adults, people with heart and lung disease, and children…because they often spend a lot of time playing outdoors and their bodies are still developing."

In addition to detrimentally affecting human health, PM also contributes to the formation of regional haze. Regional haze is the grimy-looking air that prevents one from seeing long distances. Regional haze affects our ability to enjoy scenic views in places like the Smokey Mountains. According to the EPA, sulfate particles account for 50 to 70 percent of the decreased visibility in the eastern United States.

In an effort to reduce and control the hazards associated with PM2.5, EPA issued federal standards in 1997 to be complied on a county basis. Tennessee then installed monitoring equipment to detect the ambient levels of PM2.5 in certain areas. Currently Tennessee has two counties (Knox, Hamilton) in which monitoring indicates a violation, meaning that PM2.5 levels are above the federal standard. If a county violates the standard or if relevant information indicates that it contributes to violations in a nearby area, that county will be designated as non-attainment for PM2.5. The significance of a non-attainment designation is that it places temporary restrictions on the county’s economic development and has the potential for decreased federal funding for transportation projects if attainment is not achieved by the designated timeframe.

Because of the health, environmental, and economic benefits reaped by counties with attainment status, the Department of Environment & Conservation is fully committed to ensuring that each of Tennessee’s 95 counties maintains the standards for PM2.5. One of the ways in which the department exemplifies this commitment is by participating in Visibility Improvement State and Tribal Association of the Southeast (VISTAS). VISTAS is an organization that addresses the management of haze from the platform of a regional approach.