It will depend on where the air is coming from as well as temperature and humidity. If you have light winds and high pressure you will usually have poor visibility, especially if there is a lot of industrial and traffic pollution (I expect that is often the case in LA). Winds from the sea are usually cleaner than from the land.
Often the best visibility is just after a cold front has passed through - stronger winds and lots of rain to clear the haze.
High humidity is bad for visibility as more water vapour is held in the air.