I do not know
But some folks differentiate between chemtrails and contrails (vapor)
There’s a fairly large following of the premise that a state/derp level organization has been attempting some type of aerial seeding or atmospheric modification via commercial/mil transport sized aircraft dispensing some substance into the aircrafts slipstream.
The difference between the two (contrail vs chemtrail) is basically that the latter appear in more gridlike patterns and are generally more persistant. They are also said to be associated with some type of fallout according to some observers.