Reduction of Air Pollutants| Atmospheric Pollution| AP Environmental Science| Khan Academy

- [Instructor] Hey there, friends.

Today, we're gonna learn
about air pollution.

And to start off, we're going back in time

to the small town of Donora, Pennsylvania,

in October of 1948.

(pensive harp music)

Walking into this small industrial town,

you can immediately sense
that something is wrong.

It's the middle of the day,

but there's a thick
yellowish smog everywhere,

enveloping everything and
even blocking out the sun.

It's so dark that streetlights
are on during the daytime.

It stings your eyes and it's
hard, even painful to breathe.

What we're experiencing
is the Donora Death Fog,

one of the worst air pollution disasters

in the United States.

Donora was an industrial town
full of steel plants and mills

which released toxic emissions,

such as hydrogen fluoride
and sulfur dioxide

when processing steel and other metals.

Normally, these poisonous gases

would disperse into the atmosphere.

But this time, there was
a temperature inversion,

which caused a blanket of warm air

to cover a layer of colder
air near the surface

and ride over Donora.

Consequently, the toxic emissions

were essentially trapped
under the warm air.

Over the course of several days

from October 26th to October 31st,

these toxic emissions
had accumulated so much

that half of the 14,000
people living in Donora

suffered from respiratory
problems and 20 people died.

Relief only came when the
steel mills were shut down

and a rainstorm alleviated the smog.

But following the deadly Donora smog,

the public began to
realize just how dangerous

and life-threatening
air pollution could be,

and citizens demanded change.

Donora became a turning
point in US history

and was a start of the clean air movement.

The Air Pollution Control Act of 1955

was the first piece of
US federal legislation

involving air pollution and provided funds

for research about air pollution.

Then, in 1963, the Clean
Air Act was passed,

the first federal legislation
to control air pollution,

and later expanded in 1970,
which resulted in the creation

of the US Environmental
Protection Agency, the EPA,

to develop and enforce regulations

to protect the general public

from exposure to major
outdoor air pollutants.

The Clean Air Act was expanded
in 1977 and again in 1990.

And throughout its nearly-60-year history,

our air quality has drastically improved

and pollutants have dropped sharply.

Since 1990, major air pollutants
such as carbon monoxide,

nitrogen oxides, sulfur dioxide,

and volatile organic compounds
have greatly decreased,

and that's just since 1990.

These four main air
pollutants that I highlighted

are largely released as emissions
from burning fossil fuels,

which comes from driving vehicles

and operating coal-fired power plants

and other industrial facilities.

So, as we've started to
drive more efficient vehicles

and obtain more energy from
clean renewable sources,

we've decreased the amount
of fossil fuels that we use.

And in turn, we've reduced emissions

from fossil fuels and
associated air pollutants.

But how does the Clean
Air Act work exactly?

How do we clean the air

and limit emissions of harmful pollutants?

Clean Air Act regulations
implemented by the EPA

have led to new technologies
that help to limit emissions

and remove pollutants from the air.

In particular, many of these technologies

help to reduce air pollution

from coal-burning power
plants and vehicles.

Each of these
pollution-control technologies

functions to remove harmful
components out of emissions

and release a less harmful substance.

In the last decade or so,
you've also probably noticed

more and more electric
vehicles on the road.

Improving the fuel economy of vehicles

and even using battery-powered
electric vehicles

can reduce the need to
burn as much gasoline,

thereby reducing emissions
and giving us cleaner air.

A good example is the growing demand

for hybrid and purely electric vehicles.

Here we have a simplified figure

that explains the sources of energy

for different types of vehicles

and their respective emissions.

On the left, we have
conventional vehicles,

which rely on fossil fuels
such as gasoline or diesel

and, when driven,
produce lots of emissions

like carbon dioxide and air pollutants.

Hybrid and plug-in hybrid vehicles

are similar to conventional vehicles

in that they have an
internal combustion engine,

but they also have an electric motor

which uses energy stored in batteries.

These batteries can be charged
by regenerative braking

or, in the case of plug-in hybrids,

just by using a wall outlet
or other charging equipment.

In turn, because these hybrid cars

are partially fueled by batteries,

they produce fewer emissions
than a conventional car.

Finally, vehicles that
rely solely on electricity,

known as battery electric
vehicles or BEVs,

can use an alternative electricity source

so that there's no emissions

at the source of the electricity.

What else can we do to ensure cleaner air?

We can reduce our reliance on fossil fuels

and instead invest in
cleaner renewable resources

to generate electricity such
as geothermal, wind, and solar.

And we can make decisions
in our day-to-day lives

to reduce or prevent air pollution

by using less energy
and alternative fuels.

For example, walking, biking,
or using mass transportation

can reduce the need to burn fossil fuels.

And there are plenty of other ways

to reduce our electrical needs;

in particular, using more
energy-efficient appliances.

For example, think of the LED bulb,

which uses 75% less energy
than incandescent lighting.

So, even switching out bulbs

in the lights around
your house or apartment

can make a huge difference.

But there's still many other
places out there like Donora,

and oftentimes folks living in cities

with heavy air pollution
literally can't afford to leave.

There's still much work to be done.

In Donora, though, there's
the Donora Smog Museum,

which has the tagline
"Clean air started here."

The terrible incident
suffered by Donora's community

played a huge and pivotal role

in opening the eyes of Americans

to the hazards of air pollution
and spurred political action

that's carried forth through today

and will continue into the future.

Let's all take a deep breath
and be glad that we can.