Imagine living in Los Angeles in the early 1940s—a fast growing metropolis with endless sunshine, Hollywood celebrities, suburban havens, and fancy cars. Then, imagine waking up one day, and the sun is gone, hidden behind a throat-burning noxious gas. Entire city blocks fade away, blotted out by an unexplainable gas that some thought was part of a World War II attack.
That is exactly what happened in July 1943—and then again and again for more than half a century. Without warning, noxious fog would roll in for days and sometimes weeks, paralyzing the daily activities of Los Angeles residents. Decreased visibility caused fatal collisions of cars and buses; polluted air would spread to the farms beyond the city and damage entire crops in a few hours.
It would take years for scientists to piece together the puzzle of this Los Angeles smog and decades to implement policies to improve the air we all breathe. Today, scientists are able to monitor the pieces of this puzzle from space thanks to NASA’s Aura satellite.
But what is smog? What were the pieces that made up this chemical puzzle? And how did Los Angeles free itself from this toxic nuisance and bring back “sunny California”?
Finding the pieces of the smog puzzle
The term “smog” is a contraction of the words “smoke” and “fog.” Smog usually consists of soot particles, sulfur dioxide, and other compounds. The citizens of Los Angeles initially blamed the pollution on oil refineries and factories, and they were partly right. State and local officials responded by establishing air pollution control offices, commissioning studies, restricting emissions of sulfur dioxide and smoke from power plants and industry, and banning trash-burning in backyards—a common practice at the time.
While these efforts helped reduce air pollution, they did not reduce the occurrence of smog. In October 1954, a series of intense smog events closed schools and industry in Los Angeles for almost a month. Citizens were frustrated at the lack of progress. They wanted breathable air!
The first piece to the Los Angeles smog puzzle was its smell, which was different from the sulfurous smog that claimed lives in Donora, Pa., and London, England. In those places, the culprit was the burning of coal, but there was very little of that in Los Angeles. Also, something in the Los Angeles smog was destroying rubber tires and damaging crops.
A chemist named Arie “Haagy” Haagen-Smit noticed that the smog in Southern California had a “bleach-like” odor that reminded him of a chemistry lab. In previous research, he used an apparatus to extract flavor compounds from plants to figure out, for instance, what gives pineapples their characteristic smell. Haagy decided to analyze Los Angeles's air with the same apparatus, which indicated the presence of oxidized volatile organic compounds (VOCs). So he exposed smog-sensitive plants to oxidized VOCs. Sure enough, the plants showed damage similar to plants damaged by the Los Angeles smog. Haagy thought he had the answer!
Haagy knew that plenty of VOCs were present in Los Angeles’s air, given the significant petroleum industry in Southern California and the number of cars on the road there. Gasoline is made up of organic compounds, some of which evaporate, or volatilize, in the air. (This is why you can smell gasoline fumes.) The petroleum industry in Los Angeles estimated that 120,000 gallons of gasoline were lost every day to evaporation during the refining process. Cars and trucks were equally inefficient, spewing uncombusted or partially combusted gasoline—containing volatile organic compounds—out of their tailpipes at a rate of 850 tons per day.
But when Haagy created synthetic smog in the lab, he unknowingly introduced another piece to the puzzle when oxidizing the VOCs: ozone. Oxidation is the process of combining a molecule with oxygen, and since ozone (O3) is a highly reactive molecule made of three oxygen atoms, it was the perfect compound to oxidize VOCs for his experiment.
What was oxidizing the VOCs in Los Angeles’s air? Surely, it wasn’t ozone, a powerful oxidant that was not emitted directly by tailpipes or smokestacks. Haagy and other scientists eventually figured out that nitrogen oxides in the air were reacting with the VOCs, and sunlight provided the catalyst for these chemical reactions to create ozone. Nitrogen oxides are produced during the combustion process inside car engines and are released in the exhaust.