Speaker 1: Welcome to Brainstuff, a production of iHeartRadio, Hey Brainstuff, Lauren Boblobam. Here,
Speaker 1: there aren't too many positives to be found in air pollution.
Speaker 1: It's unhealthy, unsightly, and damaging to this planet that we
Speaker 1: as a species hope to spend a lot more time on.
Speaker 1: But there's a pervasive urban legend of sorts that there
Speaker 1: is an upside here that's Smoggy Cities like Los Angeles
Speaker 1: and Beijing, which host hazy skies most of the time,
Speaker 1: at least get to have extra brilliant sunsets to cough
Speaker 1: at as a result. Could the phenomenon known as smog
Speaker 1: actually enhance sunsets? The short answer is well sort out,
Speaker 1: but only to a certain extent. To explain why, first,
Speaker 1: let's go over the science of sunsets and how different
Speaker 1: colors come to splash across the sky. To begin with,
Speaker 1: We've talked about this a bit before on the show,
Speaker 1: but it's worth going over. Basically, the sky appears to
Speaker 1: be whatever color it is due to atmospheric distortion and
Speaker 1: the limits of human eyesight. Okay, when the sun is
Speaker 1: high in the sky, its light travels a relatively short
Speaker 1: path through the atmosphere, to reach your eye. A sunlight
Speaker 1: usually appears white to our eyes because it's a mix
Speaker 1: of all of the wavelengths of visible light. You know ROIGBIV, red, orange, yellow, green, blue, indigo,
Speaker 1: and violet. Now, all of those wavelengths are different lengths.
Speaker 1: Red light has the longest among them, violet light has
Speaker 1: the shortest. The colors all have their own amount of
Speaker 1: energy too. Red light is relatively sluggish, a violet light
Speaker 1: is comparatively zippy. This stuff that makes up our air
Speaker 1: will scatter some of those wavelengths more than others. It's
Speaker 1: a phenomenon called Rayleigh scattered. Our atmosphere is composed of
Speaker 1: a very thin soup of atoms and molecules. Ninety nine
Speaker 1: percent of this soup, the broth, if you will, is
Speaker 1: atoms of nitrogen and oxygen. These atoms are tiny, hundreds
Speaker 1: of times smaller than even the shortest wavelengths of visible light.
Speaker 1: Because of that, those atoms simply don't have the power
Speaker 1: to knock around the longer wavelengths. The zippier light with
Speaker 1: shorter wavelengths is more likely to hit the tiny air
Speaker 1: atoms and get scattered around by them, bouncing until it
Speaker 1: eventually hits our eyes from any number of possible directions,
Speaker 1: meaning that violet light scatters the most. However, the sky
Speaker 1: does not appear violet during the daytime because the Sun
Speaker 1: doesn't release that much violet light and because our eyes
Speaker 1: aren't super good at detecting it. The sky instead appears
Speaker 1: blue because it is the fastest, shortest, and thus most
Speaker 1: wavelength of light that the Sun puts off a lot
Speaker 1: of and that we detect easily. But as the Sun
Speaker 1: moves across the sky, the game changes. The Earth is
Speaker 1: a sphere, so the distance between the Sun and your
Speaker 1: eye changes as the planet rotates. At high noon, the
Speaker 1: distance is the shortest. At sunset, when the sun is
Speaker 1: at the horizon, that distance is longer. When the distance
Speaker 1: is longer, there's more atmosphere for the light to travel
Speaker 1: through before you perceive it. Raleigh scattering is still an effect,
Speaker 1: but it produces an entirely different result. That's because those
Speaker 1: shorter wavelengths of light, the violet, indigo, and blue, have
Speaker 1: so much more atmosphere to travel through that they get
Speaker 1: scattered out before they reach you. That leaves only the
Speaker 1: longer wavelengths in the sky for you to see, thus
Speaker 1: turning the sunset sky all shades of yellows, oranges, and reds.
Speaker 1: The scattered blue light is busy creating a blue daytime
Speaker 1: sky somewhere else on the planet. But okay, so far
Speaker 1: we've been talking about all of this happening in a
Speaker 1: clear sky with mostly nitrogen and oxygen atoms doing the scattering.
Speaker 1: If you add other molecules into the mix, the ones
Speaker 1: in smog, for instance, the game changes again. Smog is
Speaker 1: a portmanteau of the words smoke and fog, coined in
Speaker 1: the early nineteen hundreds in London to describe the dark,
Speaker 1: foggy pollution that often hung over and through the city.
Speaker 1: It was coined specifically by people concerned with the health
Speaker 1: effects of the phenomenon at the time. A smog is
Speaker 1: made up of small particles of solids and liquids that
Speaker 1: wind up suspended in the air, called aerosols. Aerosols can
Speaker 1: come from natural sources like sea spray, trees, breathing and
Speaker 1: pollinating dust from sandstorms, forest fires, smoke and debris, and
Speaker 1: volcanic eruptions that send tons of ash into the air,
Speaker 1: but for the most part, the aerosols in big cities
Speaker 1: are human made. Think of all of this stuff we
Speaker 1: put into our air coal power, exhaust, car emissions, and
Speaker 1: gasoline fumes and the byproducts of everything from manufacturing to
Speaker 1: construction sites to cleaning solvents. Exhaust is full of nitrogen
Speaker 1: oxide compounds alike from combustion engines. Fumes can contain volatile
Speaker 1: organic compounds like from paint or petrol. It turns out,
Speaker 1: and we only figured this out in the nineteen fifties,
Speaker 1: that when exhaust and fumes combine in the air, and
Speaker 1: then that combo gets hit by sunlight, a chemical reaction
Speaker 1: occurs that produces ground level ozone and other airborne particles.
Speaker 1: Ozone is helpful when it's high up in the atmosphere,
Speaker 1: but is hazardous for us to breathe in directly so
Speaker 1: in cities. Smog is this human made mixture of chemicals
Speaker 1: composed of countless different moments of different sizes. Now, having
Speaker 1: some aerosols in the air can help scatter more light
Speaker 1: in the Rayleigh way. As long as the particles are
Speaker 1: small enough, this can bring out beautiful deep reds in
Speaker 1: the sunset. But once you've got a lot of aerosols
Speaker 1: and including particles that are closer to the same size
Speaker 1: of the wavelengths of visible light that will scatter all
Speaker 1: the colors indiscriminately. It winds up creating a washed out, grayish,
Speaker 1: hazy sky. So smoggy cities can experience extra vivid sunsets
Speaker 1: when that smog is particularly minimal. However, I also want
Speaker 1: to talk about these sometimes spectacular sunsets that occur following
Speaker 1: volcanic eruptions. After all, the aerosols released by a volcano
Speaker 1: are just another form of atmospheric pollution, right, true, but
Speaker 1: it matters what part of the atmosphere that pollution is in.
Speaker 1: Oh when we're talking about smog or the smoke from
Speaker 1: a forest fire. Those aerosols are hanging out in the
Speaker 1: layer of the atmosphere nearest to the ground, the troposphere.
Speaker 1: Here they create haze and more muted colors in the sky.
Speaker 1: But a volcano shoots aerosols all the way up into
Speaker 1: the stratosphere, higher than an airplane would go. From up there,
Speaker 1: the aerosols can bounce extra light to you for longer
Speaker 1: during a sunset, after the sun has passed below the horizon.
Speaker 1: This is also why some clouds that are way high
Speaker 1: up in the atmosphere turn brilliant shades of orange and red.
Speaker 1: During a sunset. They block any remaining blue light from
Speaker 1: above and reflect those longer wavelengths remaining, thus lighting the
Speaker 1: whole landscape up in glowing ambers. Today's episode is based
Speaker 1: on the article does smog make for Beautiful Sunsets? On
Speaker 1: HowStuffWorks dot Com? Written by Julia Layton. Brain Stuff is
Speaker 1: production of iHeartRadio in partnership with HowStuffWorks dot Com. It
Speaker 1: is produced by Tyler Klange. Four more podcasts from my
Speaker 1: heart Radio visit the iHeartRadio app, Apple Podcasts, or wherever
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