Like Los Angeles, Chile's capital is particularly prone to generating dense low-level smog. Santiago smog is not a meteorological abstraction but something you can easily see from a plane window.
Three major factors of smog in a city are surrounding mountains, cold ocean currents, and air pollution. Santiago could have all three, but it is spared the cold fog rising off the fertile waters of the Humboldt Current by the Chilean Coastal Range, the mountains which separate the Chilean Central Valley from the Pacific Ocean. This still leaves Santiago nestled in its eponymous basin between the coastal range and the Andes towering to the east, and the city’s industry and diesel traffic do the rest.
It is usually worse in the winter months, but plenty of smog was visible from the window of a plane I departed Santiago in yesterday afternoon, eastbound over the Andes:
Santiago smog is perhaps the explanation for the curious paintjob of the city’s taxicabs, a bright yellow restricted to the cars’ top halves, extending from the wipers to the C-pillars, allowing you to successfully recognize and hail one even if pollution comes in a thick layer all the way to your waist.