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Ozone Glossary
Atmosphere
The atmosphere is the column of
air that lies above the Earth's surface. The density of this air decreases as
you proceed up from the surface. The air in the atmosphere consists of 78%
Nitrogen, 21% Oxygen, and 0.9% Argon. The remaining 0.1% of the atmosphere
consists of ozone, water vapor, carbon dioxide, methane, helium, and neon. The
atmosphere is divided into different regions. The lowest two layers are the
troposphere and the stratosphere respectively. These two layers contain more
than 99% of the atmospheric molecules. 2. A unit of pressure. One atmosphere
(atm.) is equal to 760 mmHg (millimeters mercury) or 101.325 kPa
(kilopascals).
Atom
All matter is made up of atoms.
Atoms are made up of protons, neutrons, and electrons. The number of protons
an atom has, determines that atoms chemical properties. Ozone is made up of
three oxygen atoms.
Brewer Spectrophotometer
A ground-based instrument that
measures the amount of ozone in the atmosphere. The Brewer spectrophotometer
measures the amount of UV light from the sun at 5 different wavelengths
between 306 and 320 nm.
Chlorofluorocarbons (CFC's)
CFC's were used as a
refrigerator coolant and as propellants in aerosol cans. CFC's were thought of
as a great replacement for ammonia because ammonia is very flammable. CFC's
are safe, nonreactive (inert) molecules in the lower atmosphere (troposphere),
but in the stratosphere, where the UV radiation is intense, CFC's are broken
down. UV light breaks the bond between the carbon and chlorine on the CFC
molecule. With the highly reactive chlorine atom, now free, it reacts with
ozone and destroys it.
Direct Sun
Ozone measurements are often
taken with spectrophotometers using direct sunlight as the light source.
Direct Sun measurements require moderately bright sunlight. During days that
are overcast, spectrophotometers, such as the Dobson, can still take ozone
measurements using the zenith sky (light from directly overhead).
Dobson Spectrophotometer
A ground-based instrument that
measures the amount of ozone present in the atmosphere. The Dobson
spectrophotometer was designed by Gordon Dobson in the 1930's. The Dobson
spectrophotometer measures UV light from the sun at two to six different
wavelengths of between 305 and 345 nm.
Dobson Unit
The standard unit of measure
for ozone. If all of the ozone from the Earth's surface to outer space were
compressed to standard temperature and pressure (STP), the ozone layer or its
thickness would be about 3 mm thick. At STP, 3mm of ozone is 300 Dobson Units
(DU). 1mm = 100DU.
Element
An element is characterized by
a particular type of atom. The number of protons an atom contains determines
its chemical properties.
Kilometer (km)
Unit of length equal to 103
or 1,000 meters. Often referred to when measuring large distances.
Millimeter (mm)
Unit of length equal to 10-3
or 1/1000 meter. Often referred to when measuring small distances.
Molecule
Atoms combine in various ways
to form molecules. Three oxygen atoms bound together form one ozone molecule.
Nanometer (nm)
Unit of length equal to 10-9
or 1/1,000,000,000 meter. Often referred to when measuring light waves.
Ozone
Ozone is a molecule made of
three oxygen atoms bound together. Ozone is written by chemists as O3.
High energy ultraviolet light from the sun is damaging to living cells. Ozone
absorbs most high energy ultraviolet light before it reaches the Earth's
surface. Because ozone is very reactive, ozone in the air we breathe is
harmful. Ozone reacts with tissues in our sinuses and lungs. Therefore, we are
lucky that most ozone lies in the stratosphere at elevations greater than 8
km.
Ozone Hole
Since the 1970's, the amount of
ozone over Antarctica has dropped to about one third of normal levels during
the spring. This depletion of ozone, believed to be caused by chlorine put
into the atmosphere by man, is referred to as the ozone hole.
Ozone Layer
Most of the ozone in the
atmosphere is in the stratosphere (about 10 - 50 km above earth's surface).
This is what is called the ozone layer or the stratospheric ozone layer. The
layer refers to the thickness of the ozone.
Photochemical Reaction
The dissociation or excitation
of a molecule caused by the absorption of a photon. How a molecule will
react to absorbing a photon depends on the photon's energy and the molecule
absorbing the photon. Excitation of a molecule can cause the molecule to react
with other atoms or molecules more readily. Dissociation of a molecule
can cause the dissociated parts of the molecule to react more readily with
other atoms or molecules. A CFC molecule is dissociated by high energy
ultraviolet light in the stratosphere.
Photolysis
1.
(Noun) The dissociation of a molecule caused by the absorption of a photon.
2. photolyze
(Verb) The action of a molecule breaking apart after absorbing a photon. Ozone
is photolyzed by ultraviolet light.
Photon
Particles of light energy.
Spectrophotometer
Light can be separated into its
individual wavelengths by passing the light through a prism. When light passes
through matter, it may be reflected, emitted, transmitted or absorbed. By
knowing the intensity of the light before passing it through matter and
measuring the intensity of the light after it is passed through the matter,
the amount of matter in the sample can be measured.
Standard Temperature and
Pressure (STP)
0° Celcius and 1 atmosphere.
Stratosphere
The section of the atmosphere
between 8 and 16 km to 50 km above the surface of the Earth. In the
stratosphere, the temperature generally increases with increasing height, as
opposed to the troposphere, where temperature decreases with increasing
height.
Total Ozone Mapping
Spectrometer (TOMS Satellite)
The latest spectrophotometer
aboard the Earth Probe satellite launched by NASA in 1996. TOMS is a
spectrophotometer that measures the amount of ultraviolet light from the sun
that is reflected back from the Earth. The TOMS spectrophotometer measures
ultraviolet light at wavelengths between 312 and 360 nm.
Total Column Ozone
The amount of ozone contained
in a column of air. A column of air consists of the area from the Earth's
surface to outer space.
Tropopause
The tropopause is a transition
region of the atmosphere between the troposphere and the stratosphere. The
troposphere and the stratosphere have markedly different properties. The
tropopause is located just above the troposphere and just below the
stratosphere. The height of the tropopause changes during the seasons. The
tropopause is located at higher altitudes in the summer and fall and lower
altitudes in the winter and spring. This change in altitude, changes with the
abundance of ozone overhead.
Troposphere
Region of the Earth's
atmosphere that extends from the Earth's surface to between 8 and 16 km. In
the troposphere, the temperature decreases with increasing height, as opposed
to the stratosphere, where the temperature generally increases with increasing
height. The troposphere is convective, meaning that it mixes vertically.
Nearly all clouds are in the troposphere.
Ultraviolet (UV) Radiation
Light that is not visible to
the human eye. Ultraviolet light is higher in energy than visible light.
Ultraviolet light has a wavelength in the 200-400 nm region. Visible light has
a wavelength in the 400-800 nm region. The high energy ultraviolet light is
harmful to living cells in plants and animals.
UV-A
Lower energy ultraviolet light
from the Sun with a wavelength between 320-400 nm. UV-A light is not absorbed
by ozone, thus all of the UV-A light is allowed to reach the surface of the
Earth.
UV-B
Ultraviolet light from the Sun
with a wavelength between 290-320 nm. Ozone absorbs most UV-B light before it
reaches the surface of the Earth.
UV-C
High energy ultraviolet light
from the Sun with a wavelength between 200-290 nm. Ozone and oxygen molecules
absorb all UV-C light before it can reach the Earth's surface.
Visible Light
Light that is visible to the
human eye. Visible light is lower in energy than ultraviolet light. Visible
light has a wavelength in the 400-800 nm region.
Wavelength
The distance between the peaks
on a wave. A high frequency (higher energy) wave has a shorter distance
between its peaks. A low frequency (lower energy) wave has a longer distance
between its peaks.
Zenith Sky
The sky directly overhead.
Ozone measurements are often taken with spectrophotometers using the amount of
light directly overhead, rather than the light directly from the sun. Zenith
sky measurements can be taken on days that are overcast.
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