Does Smog Make Sunsets More Beautiful?

Although a little air pollution can bring out brilliant colors in sunsets, most of it just causes a washed-out haze. Learn how both sunsets and smog work in this episode of BrainStuff, based on this article: https://science.howstuffworks.com/environmental/green-science/smog-sunset.htm

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Episode Transcript

Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio, Hey Brainstuff, Lauren Boblobam. Here,
there aren't too many positives to be found in air pollution.
It's unhealthy, unsightly, and damaging to this planet that we
as a species hope to spend a lot more time on.

(00:23):
But there's a pervasive urban legend of sorts that there
is an upside here that's Smoggy Cities like Los Angeles
and Beijing, which host hazy skies most of the time,
at least get to have extra brilliant sunsets to cough
at as a result. Could the phenomenon known as smog
actually enhance sunsets? The short answer is well sort out,

(00:48):
but only to a certain extent. To explain why, first,
let's go over the science of sunsets and how different
colors come to splash across the sky. To begin with,
We've talked about this a bit before on the show,
but it's worth going over. Basically, the sky appears to
be whatever color it is due to atmospheric distortion and

(01:10):
the limits of human eyesight. Okay, when the sun is
high in the sky, its light travels a relatively short
path through the atmosphere, to reach your eye. A sunlight
usually appears white to our eyes because it's a mix
of all of the wavelengths of visible light. You know ROIGBIV, red, orange, yellow, green, blue, indigo,

(01:32):
and violet. Now, all of those wavelengths are different lengths.
Red light has the longest among them, violet light has
the shortest. The colors all have their own amount of
energy too. Red light is relatively sluggish, a violet light
is comparatively zippy. This stuff that makes up our air

(01:54):
will scatter some of those wavelengths more than others. It's
a phenomenon called Rayleigh scattered. Our atmosphere is composed of
a very thin soup of atoms and molecules. Ninety nine
percent of this soup, the broth, if you will, is
atoms of nitrogen and oxygen. These atoms are tiny, hundreds

(02:15):
of times smaller than even the shortest wavelengths of visible light.
Because of that, those atoms simply don't have the power
to knock around the longer wavelengths. The zippier light with
shorter wavelengths is more likely to hit the tiny air
atoms and get scattered around by them, bouncing until it
eventually hits our eyes from any number of possible directions,

(02:39):
meaning that violet light scatters the most. However, the sky
does not appear violet during the daytime because the Sun
doesn't release that much violet light and because our eyes
aren't super good at detecting it. The sky instead appears
blue because it is the fastest, shortest, and thus most

(03:00):
wavelength of light that the Sun puts off a lot
of and that we detect easily. But as the Sun
moves across the sky, the game changes. The Earth is
a sphere, so the distance between the Sun and your
eye changes as the planet rotates. At high noon, the
distance is the shortest. At sunset, when the sun is

(03:21):
at the horizon, that distance is longer. When the distance
is longer, there's more atmosphere for the light to travel
through before you perceive it. Raleigh scattering is still an effect,
but it produces an entirely different result. That's because those
shorter wavelengths of light, the violet, indigo, and blue, have

(03:41):
so much more atmosphere to travel through that they get
scattered out before they reach you. That leaves only the
longer wavelengths in the sky for you to see, thus
turning the sunset sky all shades of yellows, oranges, and reds.
The scattered blue light is busy creating a blue daytime
sky somewhere else on the planet. But okay, so far

(04:04):
we've been talking about all of this happening in a
clear sky with mostly nitrogen and oxygen atoms doing the scattering.
If you add other molecules into the mix, the ones
in smog, for instance, the game changes again. Smog is
a portmanteau of the words smoke and fog, coined in
the early nineteen hundreds in London to describe the dark,

(04:27):
foggy pollution that often hung over and through the city.
It was coined specifically by people concerned with the health
effects of the phenomenon at the time. A smog is
made up of small particles of solids and liquids that
wind up suspended in the air, called aerosols. Aerosols can
come from natural sources like sea spray, trees, breathing and

(04:50):
pollinating dust from sandstorms, forest fires, smoke and debris, and
volcanic eruptions that send tons of ash into the air,
but for the most part, the aerosols in big cities
are human made. Think of all of this stuff we
put into our air coal power, exhaust, car emissions, and

(05:10):
gasoline fumes and the byproducts of everything from manufacturing to
construction sites to cleaning solvents. Exhaust is full of nitrogen
oxide compounds alike from combustion engines. Fumes can contain volatile
organic compounds like from paint or petrol. It turns out,

(05:31):
and we only figured this out in the nineteen fifties,
that when exhaust and fumes combine in the air, and
then that combo gets hit by sunlight, a chemical reaction
occurs that produces ground level ozone and other airborne particles.
Ozone is helpful when it's high up in the atmosphere,
but is hazardous for us to breathe in directly so

(05:54):
in cities. Smog is this human made mixture of chemicals
composed of countless different moments of different sizes. Now, having
some aerosols in the air can help scatter more light
in the Rayleigh way. As long as the particles are
small enough, this can bring out beautiful deep reds in
the sunset. But once you've got a lot of aerosols

(06:18):
and including particles that are closer to the same size
of the wavelengths of visible light that will scatter all
the colors indiscriminately. It winds up creating a washed out, grayish,
hazy sky. So smoggy cities can experience extra vivid sunsets
when that smog is particularly minimal. However, I also want

(06:42):
to talk about these sometimes spectacular sunsets that occur following
volcanic eruptions. After all, the aerosols released by a volcano
are just another form of atmospheric pollution, right, true, but
it matters what part of the atmosphere that pollution is in.
Oh when we're talking about smog or the smoke from

(07:03):
a forest fire. Those aerosols are hanging out in the
layer of the atmosphere nearest to the ground, the troposphere.
Here they create haze and more muted colors in the sky.
But a volcano shoots aerosols all the way up into
the stratosphere, higher than an airplane would go. From up there,
the aerosols can bounce extra light to you for longer

(07:26):
during a sunset, after the sun has passed below the horizon.
This is also why some clouds that are way high
up in the atmosphere turn brilliant shades of orange and red.
During a sunset. They block any remaining blue light from
above and reflect those longer wavelengths remaining, thus lighting the
whole landscape up in glowing ambers. Today's episode is based

(07:54):
on the article does smog make for Beautiful Sunsets? On
HowStuffWorks dot Com? Written by Julia Layton. Brain Stuff is
production of iHeartRadio in partnership with HowStuffWorks dot Com. It
is produced by Tyler Klange. Four more podcasts from my
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