I know he's not the most articulate of blokes but there is no denying the fact that since this patent, Jet A1 amongst others, has been filled with all manner of additives, this includes barium salts and aluminum particulates.
For whatever reason this is, there is no denying that our skies are far murkier as a result. HK excluded, the skies here are full of so much **** anyway but from a UK perspective, I have seen a huge difference under major east west airways, crossing the Gloucestershire countryside.