Contrails

Here is a picture illustrating contrail dissipation rate being influenced by clouds:

According to the site where I borrowed this, the contrails dissipate more slowly in higher humidity - namely when they are crossing clouds. They also mention some contrails spreading out and lasting a long time, blocking the sun. Do they become bacterial? It should be easy to find out.
Update: It turns out this is a well known phenomenon but because it is promoted by conspiracy theorist, no scientist dares discuss it. Persistent contrails are called "chemtrails" and are supposed to be a government plot. It is as if anywhere there is a conspiracy theory about the government you might get close to the truth by replacing the word "government" with the word "bacteria". Anyway, that is what happens when observant people do not have the tools of knowledge and science. But no excuse exists for those with those tools who do not use them on "suspect" observations. Of course in academics, it is about self preservation. 

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