Why is the smoky mountains so smoky at times? Does pollution cause it?

No, that's a natural fog, not pollution.

Named for the blue fog or mist that hangs over the mountains and in the valleys, the Smokies were originally settled by the Cherokee. Shaconage, or “place of the blue smoke,” is what they called this range of the Appalachians.

The fog or mist is the result of warm humid air from the Gulf of Mexico cooling rapidly as it enters higher elevations. The fog is most prevalent after a summer rainstorm.

It's fog! It's truly beautiful when you drive up out of the fog bank and can view it from above.