I’m not surprised to see San Jose as #2 and Portland as #1, but I’m very surprised San Diego is not #1 or #2 or #3.
The smog is not as intense there as there is really no industry, all commercial. Furthermore when I lived there graffiti of any kind was always painted over/cleaned in a matter of days. It’s so clean there I can’t even believe it. Oh well, San Jose is good too.