In what year did the photochemical smog incident in Los Angeles occur?

From 65438 to 0943, the earliest photochemical smog event in the world occurred in Los Angeles, USA. Since then, this smog has also appeared in North America, Japan, Australia and parts of Europe. After repeated investigations, it was not until 1958 that it was discovered that this incident was caused by the exhaust pollution of 2.5 million cars owned by Los Angeles. These cars consume about 1600 t of gasoline every day, and emit more than 1000 tons of hydrocarbons and more than 400 tons of nitrogen oxides into the atmosphere. These gases are exposed to sunlight, which leads to photochemical smog events and endangers human beings.