San Gabriel Mountains on approach to LAX.

Dude I lived in central LA for years and witnessed planes spraying the grids on a weekly basis. I have so many photos and videos. Ever been out by on I-10? For some reason they do them quite a lot all the way through that area, desolate as it is. You can tell they're chemicals especially at sunset when the haze is a weird off-grey opaque color in the sun, unlike how real clouds of similar density are semi-translucent. But the big reason for suspicion is that these "trails" (the lines of clouds seen in OP's photo) expand over several hours into a pervasive haze, rather than vaporize quickly like typical airplane contrails composed of disturbed water vapor would.

Idk. What phenomenon does Science propose causes these long trail-like clouds to form at low to medium altitudes in otherwise clear atmospheric conditions?

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