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.