Traveling in North Carolina and Tennessee recently, I had the opportunity to visit Great Smoky Mountains National Park. While renowned for its “wondrous biodiversity”, the park’s name is derived from a localized atmospheric phenomenon.

The Cherokee, who originally inhabited the area, called the mountains, “Shaconage”, meaning “place of the blue smoke”. It refers to the smoke-like bluish haze that hovers over the park’s rugged peaks and valleys, especially after a rainstorm. According to the NPS, it is a natural by-product of plant transpiration.

While all trees and plants exhale water vapor, the conifer trees in the park also emit terpenes – a naturally occurring organic compound. Released in large quantities, the mix of terpenes and moisture react with natural low level ozone molecules to form tiny particles that scatter blue light. As a result, the mountains appear to be bathed in a gauzy blue mist.

In recent years, according to the NPS, human-made air pollution has been obscuring the Smokies’ signature blue haze.

View of the bluish- haze in Great Smoky Mountains National Park. Image Credit: NPS