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.