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  • 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.

Hi. It’s Mr. Andersen and this is AP environmental science video 29. It is on air pollution.

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空氣汙染 (Air Pollution)

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    Yrchinese 發佈於 2021 年 01 月 14 日
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