The reason the chem.......contrails look different is this: the vortex under the wing flows outward and above the wing inward. This 'swirls' the vortex so that the outer part of the core flows up and the inner flows down. If you view obliquely like this, it can make the vortexes appear differently to one another. Having said that, I am not sure why there appears to be such a difference in the exhaust core of the engine. Again, viewed from another angle, it probably looks the same.