When I was driving from San Diego back to Orange County on I5 North mid 70's, at around San Juan Capistrano about 50-60 miles from LA I could see a giant brown dome about 1 mile high covered LA, the dome was a little lighter by late 90's, and keep getting light every few years.
People who live in LA area(even in Orange County about 40-60 miles south of LA) more than 20-30 years can tell you how terrible the smog was before 1990.
The main problem is LA is a basin, the smog linger in the basin even they have good breeze in the afternoon from Pacific Ocean, but the mountains on the North and East keep the smog in.
The only time we can see true blue sky is after a good rain, other days are a little brown. Farther south around San Clemente all the way to San Diego we have cleaner sky.
PS Do you guys know where Californians spent their vacation ? Hawaii !
Why Hawaii when we have miles and miles of beach within 20-30 minutes drive ? Because we like the clean air of Hawaii.
The minute I had my feet on Hawaii ground I can felt the air I breath in my lungs. Every morning I went outside just to breath the air, within a day or two all my sneezing, coughing ... was gone. Within a week or two back to CA I had the same problem again.