Usually the temperature in the atmosphere decreases as you go upwards. this thermal structure aids in vertical mixing since the cold air tends to sink and the warm air heated from the sun shining on the surface tends to rise. Sometimes however an INVERSION occurs. In this case the Temp actually increases as one goes higher. this produces a relatively stable density stratification so that pollutants and sea salt and dust gets trapped in the lowest layers of the atmosphere. Another factor promoting a layer just above the surface is when high pressure forms and the winds are nearly calm the cold ocean water relative to air cools the air and allows an inversion layer to form. This radiation fog rapidly burns off once the sun rises... so expect to see the brown layer under fair skies early in the morning when it has been cold but not windy and we are having fair weather.

Actually although pollution exists in the atmosphere it can seem worse on certain days.For LA, the main reason you see it is that LA is a basin surrounded by mountains. Thus the clouds, smog sit in the basin and have nowhere to go. As for the haze being over the ocean (between the mainland and Catalina) that is because the weather moves most commonly in an off-shore pattern which means all the smog moves off land onto the ocean. When there is an onshore wind, then wind actually moves the smog inland. Another reason for the cloud cover is called an inversion. That is when the smoggy air is trapped by upper level pressure.

Yes, and in fact your eyes do not deceive you: changes in wind direction result in the pollution being blown to different areas of the L.A. basin. When the winds blow the pollution east into San Bernardino and Riverside, the bay will be clear of pollution. Similarly, rain will clear pollution out of the air. In times like these, there genuinely is less pollution between you and the island.