The Blue Haze of the Great Smokies

The Great Smoky Mountains straddling the Tennessee-North Carolina border are named for the natural blue haze that perpetually hangs over the ridges, produced by isoprene and other volatile organic compounds released by the billions of trees in the forest. The mountains are among the oldest in the world, estimated at between 300 and 310 million years, and were never covered by glaciers during the ice ages, allowing plant and animal life to persist and diversify continuously for an extraordinarily long period. The Smokies contain more tree species than all of northern Europe combined.

Source: National Park Service