If you’ve ever been among dense conifers trees, you’ll have noticed a mostly blue-ish but ranging from grey to purple haze (like the smoky mountains, or Pacific Northwest).

That’s the terpenes (and other VOC, “volatile organic compounds”) that the trees emit. These react with ozone, creating compounds that scatter blue light.

I am not certain, but I believe this fog helps plays a role (in combination with specific needle microstructures and density) in the formation of water condensation on conifer needles, which they can absorb, either via drip or more directly when it collects toward the base of the needles. The exact capability will depend on the species.

This chemical fog also acts as a communal defense against many pests and pathogens, isolated conifers are more vulnerable without it.