>>4535905 lb
To let you know, that "dark" trail was already there before the plane passed over with the contrail that you are seeing now.
You can really see this phenomena when the Sun is setting and the angel of sunlight will reveal BLACK CONTRAILS.
Black Contrails exist BEFORE the actual contrail.
Almost as if the plane is following the BLACK CONTRAIL and then spraying another chemical into it.
I am thinking that it is a catalyst. Two chemicals that combine to form another desired effect. The BLACK CONTRAIL is laid down beforehand, and for the most part–it is invisible, unless the angel of light reflects off it…visually appearing as a "shadow".