Which city is famous for its photochemical smog?

Several cities are notorious for their photochemical smog including Beijing, Mexico City and Los Angeles. The three mentioned here are just examples and not an exhaustive list. Los Angeles has had problems over the years because of the many cars, lots of sunshine, and geography and weather that tend to keep the air confined to the same area for a prolonged period. Mexico City has had problems for many of the same reasons as Los Angeles, but compounded by its high altitude which allows the UV radiation (which contributes to the formation of photochemical smog) to be more intense. Beijing suffers from heavy photochemical smog due to a combination of a large population a surfeit of heavy industry nearby and a relative lack of regulations or technologies to limit the release of the precursors to photochemical smog. Of the three cities used as examples Bejing now has, by far, the worst problems with photochemical smog. During the Bejing Olympics, they shut down most industry around the city and limited the use of cars by the population and still had very noticeable photochemical smog. Many atheletes had expressed concerns about how bad the air was expected to be in Bejing, but by implementing drastic measures, the Chinese government was able to bring it down to a tolerable level for the few weeks of the Olympics. Normal conditions in and around Bejing are normally much worse that what was present during the Olympics.