Most think that the trails are the result of additives to the fuel. Water vapor turned to ice, does not spread out over a couple hour period and turn into clouds. The barium is needed in the stratus levels to aid in weather modification experiments like the ones done by HAARP.

This is a link to the HAARP web site
HAARP Home Page

The HAARP patent includes a proposal to release large clouds of barium in order to increase electron precipitation
EASTLUND HAARP BARIUM electomagnetic weapons chemtrails