Air Pollution


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.

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