Real World: Ozone Alerts


Good ozone? Bad ozone? What’s the difference?
And why is NASA interested in measuring ozone? Find out, next, on Real World. Have you ever lived in a city that posted
an ozone alert on a really hot summer day? Just what does that alert mean and what causes
the problem? It all goes back to basic chemistry. You see the oxygen we breathe is actually
a molecule made up of two oxygen atoms, so its molecular formula is O2. Ozone is an unstable
and reactive form of oxygen that is made up of three oxygen atoms, so its molecular formula
is O3. Now, that difference of one oxygen atom might seem insignificant, but it’s actually
a huge deal. Bad ozone, or ground-level ozone, is actually
an air pollution problem that is created when pollutants like exhaust, paints, cleaning
fluids, or other industrial emissions react with sunlight, creating more of the unstable
ozone molecules. In the troposphere, which is the lowest level
of Earth’s atmosphere, and the one we’re in right now, ozone’s natural concentration is
about 10 parts per billion, or about .00001 percent of the atmosphere. According to the
Environmental Protection Agency, ozone levels greater than 80 parts per billion over a long
period of time can cause throat and lung irritation or aggravation of asthma or emphysema. And
that brings us back to those ozone alerts. When levels get high enough to cause problems,
alerts are issued and people are asked to change their regular habits — things like:
drive less, delay mowing, and stay inside if you have certain health conditions. Of course, not all ozone is bad. Ninety percent
of the ozone in our atmosphere sits in the stratosphere, the layer of our atmosphere
between about 10 and 50 kilometers above Earth. Stratospheric ozone protects Earth’ surface
from excessive ultraviolet radiation. NASA astronauts on the International Space
Station have an amazing view of our fragile atmosphere and the thin line that makes up
the ozone layer. But why is NASA so interested in ozone? Well,
let’s hear from Dr. Joe Zawodny, an atmospheric scientist at NASA’s Langley Research Center. In mid 1980s, we discovered that there was
an ozone hole in the Antarctic, and shortly thereafter we discovered that the global ozone
layer was decreasing. We discovered that the reason behind that was due to chlorine compounds
released by humans. Chlorine was seen to peak and then started to decrease in the late 1990s,
and we’ve seen global decrease in ozone flatten out. It now has a slight increasing trend. In order to understand how ozone might be
changing, it needs to be measured. The most common unit for measuring ozone is called
the Dobson Unit. One Dobson Unit is the number of molecules of ozone that would be required
to create a layer of pure ozone .01 millimeters thick. Of course, ozone isn’t all packed into
a single layer in the Earth’s atmosphere – it’s dispersed throughout it. Since NASA doesn’t have a way to actually
scoop up all the atmosphere and squeeze the ozone into layers, just how do we measure
something that makes up less than .00006 percent of our atmosphere?
For over 30 years, NASA has used the Stratospheric Aerosol and Gas Experiment, or SAGE, family
of instruments to increase our understanding of the atmosphere and our knowledge about
ozone. And the latest generation, SAGE III, is catching a ride on the International Space
Station, bringing a whole new perspective to the problem. So SAGE III measures ozone three different
ways. We use a method called solar occultation, where we look at the sun directly with the
instrument, and look through the atmosphere as the sun sets or rises. We can also do the
same thing using the moon. The moon’s a million times dimmer, so it’s a little bit more difficult,
and the third way is we can just look at scattered sunlight, just look at the atmosphere and
look at the blue sky, if you will. Molecules like ozone have unique absorption features
in them that are easily detectable. So when you see ozone vary, or if you’re measuring
surface temperature, and you want to know why you see the variability in the record
that you do, what else is going on? What the aerosols are doing, what some of the important
chemical species that control ozone, what they were doing, and only by understanding
that variability can you get at the underlying variability that you may not fully understand. The measurements collected from SAGE III will
provide valuable information to the global scientific community — helping us answer
questions like, “How is our global Earth system changing? How do human activities influence
our climate? And . . . What can we do to protect our atmosphere?” And NASA scientists will search for those
answers by using the numbers — data collected from SAGE III – to tell the story. See you next time, on Real World.

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