1943: In the middle of World War II, Los Angeles residents believe the Japanese are attacking them with chemical warfare. A thick fog that makes people’s eyes sting and their noses run has taken hold of the city. Visibility is cut down to three city blocks.

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Attack of the L.A. Smog ArchivesAs residents would later find out, the fog was not from an outside attacker, but from their own vehicles and factories. Massive wartime immigration to a city built for cars had made L.A. the largest car market the industry had ever seen. But the influx of cars and industry, combined with a geography that traps fumes like a big bowl, had caught up with Angelenos.

"People in Los Angeles were very proud of their air," said Chip Jacobs, one of the authors of Smogtown: The Lung-Burning History of Smog in Los Angeles. "They said that L.A. was the land of pure air, and that moving there could cure tuberculosis and alcoholism. They thought there had to be one simple answer."

The day after the first big smog, city officials pointed to the Southern California Gas Company's Aliso Street Plant as the source of the thick cloud. The facility manufactured an ingredient in synthetic rubber called butadiene.

Public pressure temporarily shut down the Aliso Street Plant, but the smog episodes continued to get even worse. Undeterred, Los Angeles Mayor Fetcher Bowron announced in August that there would be "an entire elimination" of the problem within four months.

But the search for the culprit of the "gas attacks" – and the ensuing battle to curb the culprit's emissions – was just beginning.

"It took them to the early 1950s for a scientist to tell Californians that the car they loved was really a death chamber, because the fumes from tailpipes were the source of their smog problem," Jacobs said. "It wasn't some factory or a slip-up at some oil plant: It was the cars that were streaming into Los Angeles."

The scientist who solved the smog mystery was Arie Haagen-Smit, a chemist at the California Institute of Technology. He was the first to recognize that ozone was the primary source of the haze. Ozone is created when partially unburned exhaust from automobiles and the hydrocarbons from oil refineries are hit by sunlight. Haagen-Smit also demonstrated that the ozone was the cause of the bleach smell L.A. residents were reporting, as well as the source of their eye irritation and respiratory problems.

Haagen-Smit "told a populace that didn't want to hear the truth," Jacobs said. "When they finally wrapped their heads around reality, they didn't blame themselves. They blamed the car companies for making defective products."

Meanwhile, L.A. built more and more freeways, and new industries came into town. The smog became commonplace.

"Throughout the '50s and '60s, some parts of L.A. were getting dangerous amounts of smog 200 days a year," said Jacobs, who grew up in Los Angeles. "There were a lot of L.A. residents who barely saw the mountains through the brown-and-orange pollution. A lot of us got used to it. That was just the way it was."

It would take another 20 years for California to finally enact decisive standards for smog pollution from vehicles. The smog laws ultimately were mirrored across the country.

Sources: 1) Smogtown, by Chip Jacobs and William Kelly

2) "The Southland's War on Smog" (South Coast Air Quality Management District)

Photo: Smog masks the Los Angeles City Hall and Civic Center in 1948.

Los Angeles Times Photographic Archive/UCLA Library