The air we breathe is this extremely precious
thing. Especially, because there is so little of
it - the atmosphere is really thin, it's like if you wrapped a single layer of plastic wrap
around a basketball. That thin sheet is what makes this tiny little
planet in the vast solar system, and as far as we know - universe - able to sustain life. We're going to look at some ways in which
human beings have negatively affected the thin layer of earth’s atmosphere by filling
it with pollutants. And spoiler alert - some of the main culprits
are these guys: vehicles and power plants - particularly those that burn fossil fuels. There’s a theme in this episode - burning
fossil fuels puts a lot of pollutants in the air we breathe. But before we get into that, let’s first
take a look at what ‘air’ or more accurately the atmosphere is. This is the atmosphere. It’s mostly nitrogen, some oxygen, a dash
of argon, and then everything else, like Neon, Helium, and Water, is a tiny sliver. And notably, carbon dioxide, a molecule we’re
going to be talking about a lot during this series, because it is so important for understanding
climate change, makes up only a very small percentage of the atmosphere. All those gases together, plus any pollutants
and dust that end up floating around make up the atmosphere. We can then divide up the atmosphere by distance
from the surface. These layers are the troposphere, stratosphere,
mesosphere, thermosphere and then the exosphere on top. We're only going to focus on two layers of
the atmosphere. The troposphere and the stratosphere. The troposphere is where most of environmental
science happens: All life forms, all biogeochemical cycles, weather patterns big and small, everything. The stratosphere is important, because that’s
where the ozone layer is. Now, a small point of clarification. Ozone is three oxygen molecules bonded together. Down here, in the troposphere, you don’t
want it, it’s real bad. It’s a pollutant that people make, a component
of photochemical smog which is just as bad as it sounds, and is related to a whole host
of respiratory issues. However, in the stratosphere, stratospheric
ozone is amazing. It’s our planet’s sunscreen. The ozone layer blocks out the vast majority
of the sun's harmful ultraviolet (UV) radiation and without it, life would not exist as we
know it. All organisms on this planet have evolved
with this small amount of UV radiation that makes it onto the surface of our planet. And that includes us - that’s why when people
go into space, radiation is a huge worry, because we aren’t built to experience the
full power of the sun. Fortunately for our soft UV-sensitive bodies,
most of the ozone in the atmosphere is up in the stratosphere, in the ozone layer. Up there, the physical properties of the ozone
molecule allow it to absorb all the UVC and most UVB radiation. UVA, and some UVB, still makes its way to
the earth’s surface. The difference between UVC, UVB, UVA - is
the energy levels, UVC has a longer wavelength, but they’re all still within the ultraviolet
section of the light spectrum. Hmm. This is getting dangerously close to physics,
so back to the ozone layer. Most ultraviolet radiation gets stopped at
the door, but some of it gets through, and it has some benefits - it helps people create
Vitamin D - but it also has risks. Exposure can cause cataracts in your eyes
or skin cancer. Wear sunscreen and sunglasses, people. However, if we didn’t have the ozone layer,
there is no amount of sunscreen that could protect us. And that almost happened. People started using these miracle chemicals
called chlorofluorocarbons, or CFCs. Long story short - that chloro - which stands
for chlorine pops off the carbon chain when exposed to UV radiation. Then that rogue chlorine tears an oxygen out
of an ozone molecule. The fancy name for this is ozone depletion,
and that led to what you might have heard referred to as the ozone hole. Fortunately, humans collectively got their
act together and banned CFCs under The Montreal Protocol in 1987. You can learn all about that in this video. Here’s the important take away - the story
of stratospheric ozone depletion is a great example of science understanding a problem,
identifying the culprit, and legislative and international bodies coming together to ban
that very substance. And eventually, seeing a recovery in our earth’s
system. Now, let’s bring it down a layer, back home
into the troposphere to talk about air pollution. Air pollution is a pretty broad category that
encompases anything in the air that harms us or any other organism. And it’s a pretty big deal: an estimated
five to six million people die every year due to air pollution - primarily from related
respiratory problems. Breathing in foreign particles and chemicals
is not good for the precious system in here In the United States, the body that is tasked
with monitoring and protecting us from air pollutants is the Environmental Protection
Agency or EPA. The EPA has six air pollutants that they continuously
monitor all over the country and they're called criteria pollutants. [I used to be really good at this] NOx, SOx,
Particulate Matter, Lead, Carbon Monoxide, and ozone. There's dozens and dozens, if not hundreds,
of different types of air pollutants out there, but these six are consistently tested and
measured all over the country because we can tie each one of them to specific human activities. Which makes monitoring and enforcing air quality
standards easier. You might have noticed a pattern in these
names. A lot have ‘Ox’ or ‘oxide’ - nitrogen
dioxide, sulfur dioxide, carbon monoxide. That oxide is a result of combustion. When things are burned that have sulfur in
it, that makes SOx, sulfur oxides. When things are burned that have nitrogen
in them, they make NOX, nitrogen oxides. If they have carbon – carbon monoxide. So if you hear oxide, or Ox - that means something
has probably been burned. For reasons I will make painfully obvious,
we’re going to talk a lot about power plant emissions this episode, so I think it is worth
taking a second to know what we’re looking at. This is a power plant and you can see two
types of smoke stacks or flues. The large one, with curved sides, that’s
a cooling tower. All that’s coming out of there is water
vapor. The smaller, thinner smoke stacks - that’s
where you’ll find the SOX, NOX, leads, and other dangerous pollutants. Okay, let’s start with NOx and SOx - why
should we be worried about these oxides? Both are highly reactive and are emitted when
fuels are burned at high temperature. For NOx, the big emitters are cars, construction
equipment, boats, and power plants. SOx comes almost entirely from coal-fired
power plants and some other industrial processes. And lucky for us, nitrogen oxides and sulfur
oxides are poisonous. They’re bad for our respiratory system,
can impact plant growth, and react with the air to make acid rain. The formal term for this is acid deposit. In the air NOX reacts to create nitric acid
and SOx creates sulfuric acid. Which then fall to the ground - its an acid
so it can burn through structures we’ve built, damaging buildings, statues, you name
it. And of course, it is dangerous to humans and
other organisms. Here’s a chart showing the critical pH levels
that organisms cannot survive in. Take this cute crayfish - below 5.5, it dies. Acid deposition lowers the pH of water and
soil, making them more acidic, and that can have serious ramifications throughout an ecosystem. The US has actually done a pretty okay job
of reducing SOx emissions from power plants, partly through regulation, improvements in
smokestack scrubbers and other cleaning technology, but also the economic viability of coal isn’t
so hot these days. So while acid deposition still has serious
consequences, it isn’t as prevalent as it once was. There’s another serious consideration when
it comes to oxides, especially NOx, and that’s photochemical smog - which we’ll come back
to later. So next on the list - this is particulate
matter - the solid stuff in the air. So not a gas like NOx and SOx, but solid particles
that are small enough to be airborne - this could be smoke, dust, or soot particles, like
ash and lead, or pollen. Near coal-power plants, having tiny pieces
of mercury in the air is not uncommon - and most of these whether from natural or anthropogenic
(the fancy word for human) sources can be dangerous to our health. The US EPA categorizes particulate matter
into two sizes, PM10, anything smaller than 10 micrometers across, and PM2.5, anything
smaller than 2.5 micrometers across. In general, the smaller the particulate matter,
the more dangerous it is to us. Particulate matter comes in many shapes, sizes
and origins. Some of which are even beneficial, important
elements of the earth system. Dust from windstorms in the Saharan desert
in Africa add phosphorus to the soils in the Amazon - an ocean away - to make up for nutrient
loss from flooding and surface runoff. Although dust particles are small, no larger
than around a tenth of the width of a human hair, they form massive plumes that can be
seen from space. This footage is from NASA's Calypso satellite. This data shows that on average, 182 million
tons of dust leaves Africa each year. 27 million tons of which ends up in the Amazon
basin. However anthropogenic sources of particle
pollution are often not so beneficial. Power plants, especially coal-fired power
plants are responsible for large concentrations of particulate matter. This map of the United States shows the concentrations
and sources for particulate matter, notice it is especially dense in the eastern US,
which is also where the majority of the US population lives. So those pollution generating plants are providing
electricity but they are also poisoning the air we breathe, where we breathe it. Relevant to right now, the spring of 2020,
the novel coronavirus has had a dramatic impact on the amount of particulate matter in the
air. This example happens to come from India. You can see in 2016, 17, 18, 19, 20 there
are heavy layers of particulate matter in the atmosphere. But now in March of 2020, we see a big drop. With much of the world sheltering-in-place
- and less vehicle traffic and different demands on power grids as a result, here India, but
also the rest of the world is producing far fewer air pollutants. Next up on the list of nasty things in the
air – lead. The main sources of lead in the United States
are smelting ore or metals processing, as well as aircraft fuel. Lead actually used to be a much bigger air
pollution problem in the US, but because of EPA regulations, we no longer use leaded gasoline
in our cars. Lead still makes the list though because it
is a scary neurotoxin that affects cognition and brain development. And if that wasn’t bad enough it persists
for a long time, especially if it’s been deposited into the soil. It is worth mentioning that lead is also a
serious water pollutant, the NRDC has a tracker that shows you all the places in the US that
exceed the EPA’s lead action level. So some of these pollutants that are dangerous
in the air because we can breathe them in, can also have serious impacts if we consume
through our drinking water, or they get into the food system. Okay, next up on our list of doom: Carbon
Monoxide. Carbon monoxide is extra devious because it
is a serious outdoor and indoor air pollutant. And like the other oxides – carbon monoxide
is produced when something is burned, like fossil fuels or biomass, or a gas stove, or
even a forest. Here you can see there is a high concentration
of carbon monoxide in the troposphere over Africa and Southeast Asia - these levels are
from massive forest fires. Carbon monoxide is colorless and odorless,
so you can't see it when it's in the air, but it is really, really toxic to us humans. It blocks the activity of hemoglobin, so our
blood can’t carry oxygen around and we suffocate. And now, let’s bring it full circle and
talk about ozone again. But remember- good up high, bad nearby. Tropospheric, or ground level ozone is a human-made
secondary air pollutant. That’s a mouthful, so let’s unpack what
that means. Ground level ozone wouldn’t exist without
people, but we call it secondary because we don’t directly produce it. Rather it’s the end result of a series of
chemical reactions. Basically, NOX from vehicle emissions plus
Volatile Organic Compounds (or VOCs) plus sunlight makes tropospheric ozone. And when that ozone is all mixed together
with the slurry of pollutants like particulate matter already in the atmosphere you end up
with photochemical smog - a dangerous thick haze that can form over large cities. That isn’t smoke, it is like the criteria pollutants combined into one
evil super-Voltron of pollution. And if you’re too young to know what Voltron
is, well this is YouTube, you can go watch a few things after we’re done. So - the criteria pollutants are super serious. And the best way to reduce the impact and
spread of these pollutants - reduced fossil fuel burning. So that means fewer coal plants and fewer
internal combustion engines. But, as I’ve mentioned a couple times, the
US has in general improved its air quality over the last several decades. And a lot of these regulations and ingenious
pollution-reducing devices, like catalytic converters reducing NOX pollution from cars,
or scrubbers in coal smoke stacks trapping sulfur dioxide, are a result of the Clean
Air Act. The Clean Air Act is up there as one of the
most fundamental and life-changing pieces of legislation ever enacted in the United
States. Effectively it gives the Environmental Protection
Agency the authority to set limits on air pollutants, and importantly enforce those
limits. Carbon monoxide, sulfur dioxide, VOCs, NOX,
particulate matter, they've all seen a dramatic decrease since the Clean Air Act. Even since 1990, we can see huge decreases
in some of these air pollutants. Compared to where the US was there have been
dramatic improvements. Though we still have a long way to go in securing
clean, healthy air for everyone. We’ve been focusing on outdoor air pollutants,
but there is a whole class of indoor air pollutants that affect human health and performance. But because they happen inside people's homes,
these are much harder to test for and regulate. Now obviously, we’ve only talked about a
handful of air pollutants and there are many many more. But there is one tricky substance in the air
that we’re going to talk about a lot in this series that we haven’t discussed in
the context of air pollution: carbon dioxide. Carbon dioxide plays a huge role in our planet’s
climate and climate change. But it isn’t really an air pollutant - at
least not in the sense that carbon dioxide itself harms human health. I mean, I'm talking right now and I'm releasing
CO2 as I breathe, but that's not the same as the criteria pollutants that we talked
about earlier. When we talk about carbon dioxide, we want
to implicate it as one of the main greenhouse gases along with methane and nitrous oxide
that are both essential to life on this planet but also in current concentrations are making
it increasingly hot in here. So to wrap up: air pollution affects human
health, animal health, and plant health. While there are natural sources of air pollution,
the most serious emitters are us, and in particular when people burn fuels or organic material. Tropospheric air pollution has seen serious
improvements in the United States thanks to the Clean Air Act and globally because of
other environmental legislation and technological advances. And way up high, the stratospheric ozone layer
is recovering thanks to The Montreal Protocol. These issues haven’t been completely solved,
but with continued strengthening of regulations and reductions in fossil fuels use we hopefully
won’t be dealing with air pollution forever.