No sauce for this but, here we go…
These X's is where HAARP, and similar technology, aim's there electromagnetic radiation. So, the theory is they put inert nano-particles into a chemtrail then HAARP targets the area were the particles are, activating them using a electromagnetic wave that turns them from inert to active. They do whatever they do and we breathe it in.
Again, no sauce, but this is this anons theory.