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