Shortly before his death in Pasadena, California, of lung cancer, the Air Resources Board's El Monte Laboratory was named after him.
He started his air pollution research in 1948, when Southern California residents suffered stinging eyes and respiratory irritation from smog.
[3] His original interest stemmed from damage to crop plants smog was causing in the Los Angeles Basin, and he had received many requests from government agencies to investigate air pollution.
[3][4] Using techniques originally developed in his work on the biosynthesis of essential oils, Haagen-Smit showed that smog primarily resulted from a photochemical reaction of the unburned hydrocarbons, ozone, and nitrogen oxides from automobile exhaust and industrial fuel combustion.
[7]: 224–226 Haagen-Smit's research led the automobile industry to install positive crankcase ventilation, the first vehicle emissions control system, in 1961.
On June 10, 1935, he married Maria "Zus" Wilhelmina Bloemers, a graduate student of botany in the University of Utrecht.