Forest Trail Explorer

US Forest Service and Southern Research Station

Airborne Particles

Clear day: little uniform haze, no cloud deposition
Cloud deposition
Uniform haze: visibility impairment before dry deposition pollutants
Fine particulates, Shining Rock Wilderness Area, August 2007

Tiny particles of matter originating from land and sea are continually emitted directly into the atmosphere and suspended in either gas or liquid form. Particulates are also formed in the atmosphere – for example, when sulfur dioxide is converted to ammonium sulfates.

Fine particles are responsible for visibility impairment, but they can also negatively impact people’s health. High concentrations of fine particulates on a daily or annual basis can increase the likelihood of respiratory or cardiovascular disease, especially for children and the elderly.

On most days in rural areas of Western North Carolina, especially when visibility is poor, ammonium sulfates make up the majority of fine particles suspended in the atmosphere. In urban areas, the addition of organic particles (sodium chloride, magnesium, sulfates, nitrates, calcium, ammonia) makes adverse health effects greater in these areas. Most of the particles that create haze come from burning fossil fuels, most notably coal (sulfate).

The U.S. Environmental Protection Agency (EPA) has established two National Ambient Air Quality Standards (NAAQS) to protect people’s health. In Western North Carolina, there are several locations measuring fine particulates. In the six locations covered by this Report, neither the daily average nor the annual average has exceeded EPA’s standards. Furthermore, the three-year average trend in fine particulates has been decreasing at most of the monitoring sites.

The above content is a part of the Western North Carolina Vitality Index. To view the full report, visit

Forest Inventory and Analysis Resources

For more information on FIA, please click here.


Colorado State University, Visibility Information Exchange Web System. "Fine particle speciation." Accessed from:

U.S. Environmental Protection Agency. "Air Explorer, Particulate Matter 2.5." Accessed from:

Photo Credits

Fine particulates:

Visibility, Shining Rock Wilderness Area: