it means you don't have much of a community

They aren't necessarily always released from the engines, but you can use optics to observe the phenomenon yourself.

Unless there are secret planes that are hidden from public eye, there are no mechanisms on private jets to allow for the release of that much water. Military/private jet's could be another story.

If you want a rabbit hole to go down, check out what aluminum-family particles do to health and nervous system development in biological systems.

There is evidence out there that suggests alum-additives are put in high-altitude jet fuels to help with efficient combustion in low-O2 environments. This is a valid chemical reaction backed up by science, as aluminum is a catalyst past a certain temp/pressure threshold. Major airlines admit to using metal additives in their fuels, but refuse to comment on which metals .

I offer no evidence to support my claims, but I encourage you to give google a shot if you want to learn more.

Well, for bio-agents I'd be real surprised if that worked. Jet exhaust is pretty hot, and it cools to an extreme rather quickly. You'd need a true extremophile to survive that temperature swing.

The second issue I would predict with this theory, is concentration. A crop dusting plane could perhaps do this within fog, but it took fire-hoses to make this work last time, which have an insane GPM capacity, which means you'd have to get thousands of gallons off the ground for every few seconds of use.

I will be the first to admit, this was the 50's, and we have likely figured out better ways to do this kind of thing since then.

Geoengineering is going on right now

You conspiracy people are slow on the news. Subverse 'news' has this story yesterday.

Did they do this to understand San Francisco's vulnerability or to is in other similarly foggy areas?

Seems like the site is down. Here is a cached version.