Hi. It’s Mr. Andersen and this is AP environmental science video 29. It is on air pollution.
When we think of air pollution today we think of cities like Beijing. I spent a week there
and I could never see the sun. In this picture you can see before and after a rain, which
has knocked a lot of those chemicals out of the atmosphere. And these chemicals have adverse
health effects. And so we saw that in Western Europe. In London, in 1952, they had the great
smog. It was difficult to see, but thousands of people died. And that led to legislation.
We had the same problems in North America. And so what is air pollution? It is not only
chemicals in the atmosphere but chemicals that have bad health effects. And since we
are breathing it in it is going to affect our lungs, our heart and can lead to increased
cancer risks. Where are these chemicals coming from? Well they can be produced naturally.
And so we have forest fires and volcanoes that can produce these pollutants. But also
we have stationary sources, you can think of those as industrial, like factories. And
then we have mobile sources. That would be like cars and buses. And so if they are effecting
us negatively we call these pollutants. And in AP environmental science you simply should
memorize the different types of pollutants that I have listed here. Starting with volatile
organic compounds or VOCs. This would be like formaldehyde, gasoline, anything that is organic
and can diffuse into the environment. We have carbon monoxide, this odorless gas. We have
NOx which is going to be nitric oxide and nitrogen dioxide. We then have sulfur dioxide
produced through the combustion of coal. We then have particulate matter. These are going
to be suspended solids. And then finally we have chemicals like lead. These are all primary
pollutants. That means they are produced by the source themselves. But they can combine
with other chemicals in the atmosphere and produce secondary pollutants. So for example
NOx can produce nitric acid. And sulfur dioxide can produce sulfuric acid. And these combined
can produce acid rain or more generally acid deposition that has huge impacts on life.
And then one of the pollutants that you are probably most familiar with is ozone that
can be produced through sun. And also we need nitrogen dioxide to produce that. And if we
can combine a lot of these then we have smog. It is probably the most famous type of air
pollution that you are familiar with. And it is exacerbated by things like temperature
inversions. So how do we control air pollution? Well with regulation is one way. The clean
air act in the United States was able to reduce pollutants and save lives. And so technology
is able to scrub those pollutants out of the air before it is released. Where is the air
pollution coming from? What are the sources? They can be stationary, like this factory.
They could be mobile like all of these cars stuck in traffic. Or it can be natural, remember,
like a giant forest fire can increase the amount of air pollution. But regardless, how
do they affect us? It is through our cardiovascular system. It is just like smoking. You can think
of it that way. It can lead to lung disease, heart disease and increased risks of cancer.
And so where do we see these health effects most? It is wherever we have industrialization.
So clearly it is going to be in places like China, but look over here on Eastern Europe.
We have a huge amount of industrialization and not a lot of regulation. And so let’s
go through those primary pollutants again. We have VOCs, which are volatile organic compounds.
An example could be this gasoline that is evaporating into the environment. Formaldehyde.
If you smell a pine tree, those are VOCs or organic compounds that are coming off and
can lead to things like smog. We have carbon monoxide which is produced naturally through
photochemical sources. But it can also be produced through combustion. All of these
sources produce carbon monoxide. We then have NOx which is going to be nitric oxide and
then nitrogen dioxide. It is this brown gas that contributes to that color that you see
in smog. We then have sulfur dioxide. You have probably smelled that if you have ever
been around a coal plant. And you can see here that in the US it is going to be restricted
to the East coast generally because we are going to have more industrialization there.
And then we have particulate matter. These are going to be small solids. This is from
the EPA, so you can think of sand as an example of a particulate. But it is not small enough.
And so this is your hair. It is going to be on the order of 50-70 microns. And so we are
talking about things that are smaller than that. Small sediments that as you breathe
it in the hairs in your nose and respiratory track do not trap it. It goes into your lungs,
and just like smoking, it is stuck there and can lead to other types of diseases. And then
we have chemicals like lead. We used to add lead to our gasoline. And there are huge neurological
impacts of lead. Now again these primary pollutants can produce secondary pollutants. And so the
nitrogen and the sulfur can lead to nitric acid and sulfuric acid. And these lead to
acid rain. It can dissolve statues like this, but more importantly it changes the pH in
the whole food web and can impact living systems. And then we have ozone. Ozone we have talked
about before can be good. And so if we look at the stratosphere, way up here in the stratosphere
remember the ozone which is produced naturally is blocking harmful UV rays. But if we move
down near the earth it produces a tropospheric ozone, we call that bad ozone. It is one of
that large things that contributes to smog, photochemical smog. And so photochemical smog,
this is some in Mexico City, you can almost draw a line here and say the smog is below
that line. Well what you are looking at there is a temperature inversion. And so the heat
is inverted. Let me show you what that looks like. And so if we have, in this environment,
the sun is heating the earth. And so we are going to have the air near the earth warmer.
And so if we look at that gradient it is going to go from warm at low altitude to cool and
then cooler air as we move up. And this gradient is going to move a lot of those pollutants
up and then away from that city or wherever they are produced. But sometimes due to currents
or wind or just the geography of the city you can get what is called an inversion. And
so instead what we have is a layer of cooler air near the earth. And so it is inverted.
And so as we move up it gets warmer. And then it gets cooler after that. So what you are
doing is you are trapping all those pollutants near the surface of the earth. They cannot
move up and the cannot move away. And then we start to have chemical reactions going
on. And so photochemical smog is caused by these three things, NOx, VOCs and the sun.
And so if we look at that chemically, this is nitrogen dioxide. And if you have sunlight
what happen is that will break a free oxygen atom away. Now that free oxygen atom can then
combine with atmospheric oxygen and it can produce this ozone. And so what is smog? It
is essentially these NOx compounds and then this ozone. But naturally what will happen
is that these will spontaneously move back to nitrogen dioxide and regular tropospheric
oxygen. And so again, to make smog we have to have not only NOx and then sun but we have
to have these volatile organic compounds as well. And so how does it work? We break apart
that nitrogen dioxide again. So we are producing this nitric oxide. And that will combine with
these volatile organic compounds in the atmosphere itself. And so now what happens is that we
produce this ozone but it is not spontaneously going to go back again. And so how do you
form smog? We have to have these volatile organic compounds. We have to have this nitrogen
dioxide. And then we have to have sunlight. And so areas like Los Angeles where all of
these come together have a huge amount of smog. How do we prevent it? We prevent the
amount of nitrogen dioxide and we prevent the amount of volatile organic compounds in
the atmosphere. Now how do we eliminate air pollution? We do that through legislation.
So we have restrictions on the amount of pollutants. And so the clean air act is probably the most
famous one in 1970. And what they did is they put strict standards on these pollutants over
here. And so in industry you are limited on how many of these pollutants you can put into
the atmosphere. But how do we do that? Technologically we can use a catalytic converter. This is
essentially grabbing onto that nitrogen dioxide and carbon monoxide that is produced in combustion.
We can then use mechanical filters or electrostatic filters like this. They will produce a gradient
and it grabs on to some of these pollutants. We can scrub the air. And we can use wet scrubbers
as well. So as the air goes in, the polluted air goes in, we have a mist eliminator so
there is water here and that water will grab onto a lot of those chemicals. They will move
down into this packing material and then the clean air is going to go out the other side.
And so did you learn the following? Could you pause the video at this point and go through
and fill it all out? Well let me do that for you. It can cause lung disease, heart disease
and then increased cancer risks. Those chemicals could come naturally. The could come stationary
or mobile sources. We can control that through the clean air act and technology and regulation.
If we look at the pollutants themselves, again in review, it is VOx, carbon monoxide, NOx.
That produces nitric acid. We have sulfur dioxide, particulate matter and then things
like lead. These acids can lead to acid deposition. And the combination of all these produces
smog which is exacerbated by temperature inversions. And so that is air pollution. It is deadly
if we do not regulate it. And I hope that was helpful.