I think they spray all the time. Probably a fuel additive. I don't know. Sometimes the atmospheric conditions show what's going on, other times you don't see it. If you recall 10 years back or so, the trails would hover for about 30 minutes before disappearing. Now they last throughout the day which makes me think something has changed or intensified. All I can share are my observations but so far they are more valid than the authority assurances.