what is in the chem trails?

I live about 20 miles south east of the Salt Lake International airport and about 40 miles south east of Hill Airforce base and it seems like we have a constant flow of chem trails in the sky.
It is not the exhaust from the Jets flying in and out of the commercial airport.
I say this because there are hundreds of flights in and out every day and if that was the source then there would be hundreds of trails a new one every couple minutes and they would all be heading north or south because that is where the runways are that they fly in and out of.

Hill Airforce base flys jets also but their test bombing rang is way west of here and so far away that we never see them flying over the test range.
There are 3 chem trails that I can see now by looking out my window.
As soon as they begin to dissipate new ones appear and it goes on and on and on.
Are these safe to breath?