One sunny summer day in 1943, a blue-brown haze descended upon the city of Los Angeles. It smelled like bleach, made people’s eyes sting and drove almost everyone indoors. It was so bad that some residents thought they were under a chemical warfare attack. This was Los Angeles’ first episode of “photochemical” smog.

A general description is given of the famous 1940 photochemical smog in Los Angeles, characterized by plant damage such as silvering of the lower surface of cereal and tobacco leaves and by eye-irritation, quite different from the previously recognized smog due to sulfur dioxide. The study of the origin and cause of Los Angeles smog is described.

In a Plexiglas chamber set up in the parking lot of the Los Angeles County APCD's Vernon headquarters, researchers created smog by exposing auto exhaust to sunlight. APCD employees voluntarily exposed their eyes to smog from the chamber while workers with stopwatches timed how long it took for tears to stream down the volunteers' faces.