PBS Terra on YouTube recently did an episode about the blue haze over forests in (IIRC) Tennessee. Trees emit VOCs that make the air hazy. The blue haze from

PBS Terra on YouTube recently did an episode about the blue haze over forests in (IIRC) Tennessee. Trees emit VOCs that make the air hazy. The blue haze from trees was being replaced by brown haze from industry. Maybe tree smog is safe to breathe, but trees do create smog in at least some places.