Those Smoky Mountains — What Makes the Blue Ridge Blue?

Ever wonder why the Smoky Mountains and Blue Ridge Mountains have those names? The Cherokee referred to their mountain homeland as Shaconage (shah-CON-uh-gee), or land of the blue smoke. European settlers borrowed the concept and came up with the Great Smoky Mountains and the Blue Ridge Mountains.  Today, you’ll find several national park units here, including Great Smoky Mountains National Park, Shenandoah National Park, the Blue Ridge Parkway, and the Appalachian National Scenic Trail.

So, what is it about these places that conjure up these smoky blue images? Is it:

• A. Blue flowers famous from the area during spring and summer, 
• B. Kentucky bluegrass in the meadows,
• C. Recurring forest fires with bluish-gray smoke, or
• D. East coast smog and pollution?

Actually, it’s none of the above. All those trees, bushes, flowers, ferns, and other plants have to breathe, just like us. But unlike us, where we exhale carbon dioxide laden air, the vegetation exhales something called volatile organic compounds.  Yikes! That sounds like pretty nasty stuff, and some VOCs like paint fumes and petroleum distillates really are bad for us and can often be flammable as well.  But plants can also give off natural VOCs — not nearly as bad for us as dry cleaning products or aerosol fumes.

To get technical on you, Volatile Organic Compounds are defined as organic chemicals that have a high vapor pressure and easily form vapors at normal temperature and pressure. You know that great pine smell that permeated your living room when you hauled in the freshly cut Christmas tree last month?  Those are VOCs you’re smelling. Rub those pine needles in your hand or just bring the tree into a warmer house and the smell gets even stronger because by doing so, you’ve helped release them into the air.

The class of VOCs called terpenes (as in turpentine) are naturally occuring hydrocarbons emitted by conifers. Two types of terpenes known as α-pinene and β-pinene are even used in the chemical communication system of insects!  Who knew?  In the wild and in much larger numbers, all these tiny molecules join forces to form new particles that scatter blue light from the sky.  So when you look at the mountainscape, it’s like wearing Carolina blue-tinted sunglasses.

So, do you think maybe Elvis Presley’s song Blue Christmas was talking about Volatile Organic Compounds invading Graceland every December?   Well, probably not.  For just that one tree to make a blue tinted living room, there’d have to be a whole lotta shakin’ goin’ on!

Parke Diem!
— Jon