The Blue Ridge is blue because the trees exhale

On a hot day a forest breathes out isoprene and other volatile compounds, partly to protect its own leaves from the heat.

Sunlight goes to work on them and builds particles so small that they scatter blue light more strongly than any other color.

That haze lying over the Blue Ridge and the Great Smokies is not smoke and it is not water vapor. It is the forest’s own breath, hanging in the air, catching the light.

When walking in the woods, what is the weirdest thing you’ve ever smelled?

Sources

• Air Quality, Great Smoky Mountains — National Park Service

Sources checked 2026-08-12.