In the United States, where the development of motorization took place about 20 years
earlier than in our country, it is reported that the city of Los Angeles experienced the
problem of air pollution due to photochemical smog as early as the late 1940's. In
1950 Haagen-Smitl. reported the this new type of air pollution was the gas which was
produced in the atmosphere, when the exhaust gas emitted by automobiles reacted to the
sunlight. The pollutant gas resulted in doing harm to plants, and causing irritation of the
eye and even the cracking of tires.