I am trying to find a good place to gather usnea lichen. I keep reading how sensitive it is to air pollution, but don't know how far I need to be for it to be ok. I found a place that seems pretty good but it's only about 5 minutes outside of a somewhat busy suburban area. Had to hike to the back side of a small lake before I found much but could still hear some cars in the distance. I'm thinking this is probably not far enough but not sure what kind of radius I should be looking at.