I first flew into LA in 1959 and from the airplane you could see a pink smog dome. In fact, the pilot pointed this out to us passengers. So, that smog dome is appreciable and has been there for nearly 1/2 century.

As for residues, only pure hydrocarbons can clean without residue! Others may work but may leave a residue. Residue is often unimportant with solid state devices, but residue is critical when working with devices that have moving parts. And so, you have to take that into consideration with camera equipment vs electronic equipment.