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It was the worst air pollution

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attack in the United States 
history.

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[Announcer voice] “A death bring

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over Pennsylvania's bustling 
industrial town of Donora.

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Residents have difficulty 
in breathing the murky air

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as the town 
is plunged into darkness.”

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Twenty people died.

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It was almost instantaneous.

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People were choking 
in the streets.

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Newspapers grabbed 
hold of the story

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and it began to run 
wild across the country.

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Donora prompted

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scientific investigation

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to try to figure out 
what was going on.

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And the major breakthrough came 
from a surprising place.

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In the 1950s, the 
Dole Fruit Company

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was the world's 
largest producer of pineapples,

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and it had an interest in 
using a new chemical technique

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to better understand 
its big moneymaking product.

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Could you replicate the flavors?

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Could you make 
artificial flavors?

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One of the most promising plant 
chemists at the time was

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Dr. Ari Haagen Smit 
at Caltech in Pasadena.

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And he's funded by pineapple 
growers.

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His specialty was isolating 
plant proteins,

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basically to figure out 
all of the chemical explanations

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for why pineapples 
smell like pineapples.

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It turns out that

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agriculture 
is really affected by smog.

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And one of the things 
that gets him into studying

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what is happening to air quality 
in Southern California

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is that crops are dying,

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and they are desperate 
to figure out why.

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What Haagen Smit did 
was to take actual air

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and deconstruct it, to show 
what was making up the substance

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that was damaging 
leaves and plants.

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His initial approach

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to figuring out what was in 
the air was to use exactly

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the same processes 
that he'd used for pineapples.

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He drew in about 500 cubic feet 
of air, about the amount

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that a typical person 
would breathe in a day.

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And when all of that 
got distilled down

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into just a few drops 
of really terrible

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smelling brown liquid: 
distilled smog.

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Haagen Smit

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was able to study it 
at a molecular level.

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And one of the important 
findings was that

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this was not a sulfur problem, 
which was what had happened

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in Donora, Pennsylvania, 
in other industrial cities.

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Actually, 
what he was finding was

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large concentrations of ozone.

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But it was a bit of a mystery

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because there were no sources 
of ozone in Los Angeles.

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This is not something that 
industrial factories just emit.

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So something else is going on.

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The other thing 
Doctor Haagen Smit discovers

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when he analyzes the air is 
that there's a component in it

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that comes from petroleum

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hydrocarbons.

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Hydrocarbons are actually a part

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of fossil fuelsof gasoline.

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When gasoline evaporates, 
it releases hydrocarbons

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into the air that 
combine with other chemicals.

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But he discovers that smog

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is actually not just 
about the chemicals

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it's also about the sun.

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It's the interaction 
of the hydrocarbons

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with a mix of chemicals in the 
air being exposed to the sun

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that creates ozone.

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And of course, Southern 
California has sun in abundance.

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So the first thing he decided 
to do was to try to recreate

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smog in the laboratory.

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[Interviewer] “This device here 
recreate smog

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as we breathe it 
in Los Angeles.”

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[Haagen Smit]: “That's right.

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There is an abundance of ozone 
formed here in the air.

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And it reacts with, gasoline.”

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[Interviewer]: “And this, this 
then that you're making will be

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what we're breathing today 
here in Pasadena.

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[Haagen Smit: “That is a pretty 
duplication of it.

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The hydrocarbons in the air form 
ozone in the sunlight.

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And that is the beginning 
of our trouble.

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Then we take some gasoline 
and the vapors of the gasoline.

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You will see react now 
as the ozone.

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And we get concentrated smog.”

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His great discovery 
is that the combination

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of the ozone, the hydrocarbons, 
and their exposure

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to sunshine creates 
ozone pollution.

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Doctor Haagen Smit 
calls this photochemical smog.

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To learn more, watch

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Clearing the Air: 
The War on Smog

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from American Experience.