When President Barack Obama gave a major address on climate change on June 25, 2013, he reached back more than three decades for a personal anecdote to support his argument.

"Now, what you'll hear from the special interests and their allies in Congress is that (my climate change plan) will kill jobs and crush the economy and basically end American free-enterprise as we know it," Obama said. "And the reason I know you'll hear those things is because that's what they said every time America sets clear rules and better standards for our air and our water and our children's health.

"And every time they've been wrong," Obama continued. "when I was going to school in 1979, 1980 in Los Angeles, there were days where folks couldn't go outside -- and the sunsets were spectacular -- because of all the pollution in the air.

"At the time when we passed the Clean Air Act, to try to get rid of some of this smog, some of the same doomsayers were saying, ‘New pollution standards will decimate the auto industry.’ Guess what? It didn't happen. Our air got cleaner."

Many Twitter users asked us whether it was really true that during Obama’s days in Los Angeles "there were days where folks couldn't go outside. … because of all the pollution in the air."

We’ll start with some background on smog. The smog predominant in Los Angeles -- formally known as "photochemical smog" -- is created when light reacts with motor vehicle and industrial emissions to form ground-level ozone. This ozone can make it difficult to breathe, causing asthma attacks and lung inflammation, as well as making eyes itchy and watery.

In the United States, at least, Los Angeles has been ground zero for smog for decades, due to its heavy automobile usage, its industrial base and the presence of mountains and valleys, which prevent polluted air from floating elsewhere. Los Angeles smog emerged in the 1940s and worsened from the 1950s to the 1970s. It got so bad in October 1954 that the city virtually shut down for the entire month (and gas masks were common, as the photograph below illustrates). Smog became so closely identified with Los Angeles that "smog in a can" became a popular gag gift.

Today, Los Angeles still has smog -- in April 2013, the American Lung Association ranked L.A. first in the nation for ozone pollution, as well as fourth for particulate pollution such as dust and soot. But concerted environmental efforts have reduced the extent of the problem significantly.

In rising order of seriousness, smog alerts for southern California start with health advisories and move upwards to stage 1, stage 2 and stage 3. The last stage 3 smog alert came in 1974 -- so long ago that Ronald Reagan was still governor. The last stage 2 alert came in 1988, and there has been only one stage 1 alert since 1998 (it came in 2003).

"Peak ozone levels in southern California today are roughly one-third of what they were in the late 1970s, due to aggressive and innovative air pollution controls here," said Sam Atwood, a spokesman for the South Coast Air Quality Management District, the air-pollution control agency for Los Angeles, Orange County and portions of Riverside and San Bernardino counties.

So what would Obama have experienced when he was a student at Occidental, the college he attended before transferring to Columbia University for his junior and senior year? We can approximate the impact based on statistical and anecdotal evidence.

Occidental, located in the Eagle Rock neighborhood northeast of downtown L.A., would have been subject to many of the smog risks typical of the region from 1979 to 1981.

According to South Coast Air Quality Management District data, a health advisory -- a comparatively low-level alert -- was issued somewhere in the agency’s region of jurisdiction 169 times in 1979, 152 times in 1980 and 159 times in 1981. The stage 1 threshold was met 120, 101, and 99 times during those three years.

Even allowing that Occidental itself may have experienced just a fraction of these episodes, the university still would have faced a significant number.

So what did these advisories mean in a practical sense? For a health advisory, the lowest of these levels, all children are supposed to "discontinue prolonged, vigorous outdoor exercise lasting longer than one hour," and "susceptible persons, such as those with heart or lung disease" should "avoid outdoor activity," including "calisthenics, basketball, running, soccer, football, tennis, swimming laps, and water polo."

For the more severe stage 1 episodes, all children are supposed to "discontinue all vigorous outdoor activities regardless of duration," including "physical education classes, sports practices, and athletic competitions."

Finally, for stage 2 or stage 3, all children are supposed to "discontinue all outdoor activities."

This suggests that Obama’s claim is slightly exaggerated. He said that "there were days where folks couldn't go outside," but nothing in the rules addressed what healthy adults could do, including healthy college-age kids. Rather, the rules addressed adults with compromised health as well as children.

Still, the reality of smog alerts was not pretty, and by all accounts, staying inside, if feasible, was certainly preferable.

The White House pointed us to a Newsweek article from Sept. 24, 1979, when Obama was just settling in at Occidental, that documents what it called the worst L.A. smog in 24 years. "Tennis courts stood empty," the article said. "Golf courses lay nearly deserted. Schools canceled recess, and the usual parade of joggers around Pasadena's Rose Bowl dwindled to just a handful."

We found other first-hand testimony. Char Miller, a professor of environmental analysis at Pomona College in the Los Angeles suburb of Claremont, recalls enduring smog alerts when he was a student at neighboring Pitzer College in the mid 1970s. "There were way too many days when you could not see the mountain that today frames my office window," he said. "It was possible to not know it was there for months at a time."

And William Kelly, the co-author of Smogtown: The Lung-Burning History of Pollution in Los Angeles, recalls attending Occidental a few years before Obama.

"When I got there in 1973, I played a vigorous game of basketball in an un-air-conditioned gym," Kelly said. "I don't remember the end of the game, just waking up in the early evening with a pounding headache and watering eyes and wheezing in my dorm room. Turns out there was a stage 2 smog alert going on that afternoon, and I didn't have a clue."

Our ruling

Obama said that as a student at Occidental College in Los Angeles from 1979 to 1981, "there were days where folks couldn't go outside. … because of all the pollution in the air."

The idea that "folks couldn’t go outside" is an oversimplification. The advisories -- and they were only advisories -- were aimed at children and people who had existing health concerns. But Obama is right that smog was a severe problem at the time in the Los Angeles region. On balance, we rate his claim Mostly True.