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Ozone
named
from the Greek "ozein" for smell. Pronunciation: 'O-"zOn
Function:
noun
Etymology:
German Ozon, from Greek ozOn, present participle of ozein to smell
Ozone
is a molecule that contains three atoms of oxygen and thus has the formula
O3.
Ozone
was first discovered in 1839 by German scientist Christian Friedrich
Schonbein.
Ozone - Good Up High Bad
Nearby
NASA
Graphic
It
is a pale blue, relatively unstable molecule made up of three oxygen atoms. The
ozone molecule is angular, polar, and diamagnetic. Both oxygen bond lengths
(1.28 angstroms) are identical. It is formed from molecular oxygen (O2) by
ultraviolet and extreme ultraviolet photolysis followed by recombination of
atomic oxygen (O) with O2.The name ozone is derived from a Greek word meaning "to
smell". It may also be formed by passing an electrical discharge
through gaseous oxygen. It is characterized by a unique odor that is often
noticed during electrical storms and in the vicinity of electrical equipment. In
fact, the term ozone is derived from the Greek word ozein which means "to
smell." The density of ozone is about 2.5 times that of O2. At -112 degrees
C it condenses to a deep blue liquid. It is a powerful oxidizing agent and, as a
concentrated gas or a liquid, is highly explosive. Excess oxygen atoms, also
known as free radicals, oxidize materials that they contact and are associated
with the aging process.
Credit:University
of Alaska
Ozone is a relatively simple molecule, consisting of three
oxygen atoms bound together. Yet it has dramatically different effects depending
on where ozone resides, it can protect or harm life on Earth. High in the
atmosphere about 15 miles (24 km) up ozone acts as a shield to protect Earth's
surface from the sun's harmful ultraviolet radiation. Without this shield, we
would be more susceptible to skin cancer, cataracts, and impaired immune
systems.
Closer
to Earth, in the air we breathe, ozone is a harmful pollutant that causes damage
to lung tissue and plants. Near Earth's surface, where ozone comes into direct
contact with life forms, it primarily displays a destructive side. At ground
level, ozone is a health hazard it is a harmful pollutant that causes damage to
lung tissue and plants- it is a major constituent of smog.
Earth’s atmosphere
NASA GSFC Graphic
Because
it reacts strongly with other molecules, large concentrations of ozone near the
ground prove toxic to living things. Motor vehicle exhaust and industrial
emissions, gasoline vapors, and chemical solvents are some of the major sources
of NOx and VOC, also known as ozone precursors.
 
Environmental
Protection Agency graphic
Strong sunlight and hot weather cause
ground-level ozone to form in harmful concentrations in the air. Many
urban areas tend to have high levels of "bad" ozone, but other
areas are also subject to high ozone levels as winds carry NOx emissions
hundreds of miles away from their original sources.
At higher altitudes, where 90 percent
of our planet's ozone resides, it does a remarkable job of absorbing
ultraviolet radiation. In the absence of this gaseous shield in the
stratosphere, the harmful radiation has a perfect portal through which to
strike Earth. The amounts of "good" and "bad"
ozone in the atmosphere depend on a balance between processes that create
ozone and those that destroy it. An upset in the ozone balance can have
serious consequences for life on Earth. Scientists are finding evidence
that changes are occurring in ozone levels—the "bad" ozone is
increasing in the air we breathe, and the "good" ozone is
decreasing in our protective ozone shield.
Factors influencing Ozone
concentrations
- Stratospheric sulfate
aerosols: large explosive volcanoes are able to place a significant amount
of aerosols into the lower stratosphere, as well as some chlorine. Because
more than 90% of a volcanic plume is water vapor most of the other
compounds, including volcanic chlorine, get ''rained-out'' of the
stratosphere. The effects of a large volcano on global weather are
significant, which in turn can affect localized weather patterns such as the
antarctic ozone hole. Many observations have linked the 1991 Mt. Pinatubo
eruption to a 20% increase in the ozone hole that following spring[Solomon
et al. 1993]) . The effects of a large volcanic eruption on total global
ozone are more modest (less than 3%) and last no more than 2-3 years.
- Stratospheric winds: every 26
months the tropical winds in the lower stratosphere change from easterly to
westerly and then back again, an event called the Quasi-biennial Oscillation
(QBO). The QBO causes ozone values at a particular latitude to expand and
contract roughly 3%. Since stratospheric winds move ozone, not destroy it,
the loss of one latitude is the gain of another and globally the effects
cancel out.
- Greenhouse gases: to the
degree that greenhouse gases might heat the planet and alter weather
patterns, the magnitude of the stratospheric winds will certainly be
affected. Some of the more popular scenarios of global warming predict
cooler stratospheric temperatures, leading to more polar stratospheric
clouds
and more active chlorine in the area of the antarctic ozone hole.
- Sunspot cycle: ozone is
created by solar UV radiation. The amount of UV radiation produced by the
sun is not constant but varies by several percent in a roughly 11year cycle.
This 11year cycle is related to magnetic changes within the sun which
increase the solar UV output, and is heralded by an increase sunspots which
appear on the surface of the sun. Comparisons of yearly ozone concentrations
show a small 11 year variation in global ozone of about 2%. Episodes of
unusual solar activity, solar storms and large solar flares, could certainly
alter this value.
- Stratospheric chlorine, coming
mostly from man-made halocarbons. Careful subtracting of other natural
factors yields a net decrease of 3% per decade in global ozone,1978-1991;
due most likely to catalytic degradation by stratospheric chlorine
Credit:
EPA,NASA,NOAA
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