Column Ozone: ozone between the Earth's surface and outer
space.
Ozone levels can be described in several ways. One of the most
common measures is how much ozone is in a vertical column of air.
The dobson unit is a measure of column ozone.
Other measures include partial pressure, number density, and concentration
of ozone, and can represent either column ozone or the amount
of ozone at a particular altitude.
Dobson Unit (DU): a measurement of column
ozone levels.
If 100 DU of ozone were brought to the Earth's surface, it would
form a layer 1 millimeter thick. In the tropics, ozone levels
are typically between 250 and 300 DU year-round. In temperate
regions, seasonal variations can produce large swings in ozone
levels. For instance, measurements in Leningrad have recorded
ozone levels as high as 475 DU and as low as 300 DU. These variations
occur even in the absence of ozone depletion, but they are well
understood. Ozone depletion refers to reductions in ozone below
normal levels after accounting for seasonal cycles and other natural
effects. For a graphical explanation, see NASA's
TOMS site.
Montreal Protocol: the international treaty governing the
protection of stratospheric ozone.
The Montreal Protocol on Substances That Deplete the Ozone Layer
and its amendments are the international treaties requiring that
countries end production of ozone-depleting substances. Under
the MP, several international organizations report on the science
of ozone depletion, implement projects to help move away from
ODS, and provide a forum for policy discussions. In addition,
the Multilateral Fund provides resources to developing nations
to promote the transition to ozone-safe technologies. The full
text of the MP is available online.
Nanometer: a distance of one billionth of a meter.
The nanometer, or nm, is a common unit used to describe wavelengths
of light or other electromagnetic radiation such as UV.
For example, green light has wavelengths of about 500-550 nm,
while violet light has wavelengths of about 400-450 nm. One billionth
is a tiny number. One foot is about one billionth the distance
of 48 round-trips between Los Angeles and Washington, DC.
Ozone: a gas composed of three atoms of oxygen.
Ozone is a bluish gas that is harmful to breathe. Nearly 90%
of the Earth's ozone is in the stratosphere
and is referred to as the ozone layer. Ozone
absorbs a band of ultraviolet radiation called UVB
that is particularly harmful to living organisms. The ozone layer
prevents most UVB from reaching the ground.
Ozone Depletion: Chemical destruction of the stratospheric
ozone layer beyond natural reactions.
Stratospheric ozone is constantly being created and destroyed
through natural cycles. Various ozone-depleting substances (ODS),
however, accelerate the destruction processes, resulting in lower
than normal ozone levels. Because ozone absorbs UVB,
less ozone will allow more of this harmful solar radiation to
reach the Earth's surface. The
science section of EPA's ozone depletion Web site offers much
more detail on the science of ozone depletion.
Ozone Depletion Potential (ODP): a number that refers to
the amount of ozone depletion caused by a substance.
The ODP is the ratio of the impact on ozone of a chemical compared
to the impact of a similar mass of CFC-11. The ODP of CFC-11 itself
is defined to be 1.0. Other ozone-depleting substances have ODPs
ranging from 0.02 to 10. Several classes of substitutes have zero
ODP because they do not contain chlorine.
Ozone layer: the region of the stratosphere
containing the bulk of atmospheric ozone.
The ozone layer lies approximately 15-40 kilometers (10-25 miles)
above the Earth's surface, in the stratosphere. Depletion of this
layer by several chemicals produced through human activities will
lead to higher UVB levels, which in turn will
cause increased skin cancers and cataracts and potential damage
to some marine organisms, plants, and plastics. The
science section of EPA's ozone depletion Web site offers much
more detail on the science of ozone depletion.
Solar noon: the time during the day when the sun appears
to have reached its highest point in the sky. Usually, this is not
the same time as "clock noon". The relationship between
clock noon and solar noon depends on your location within your time
zone and the time of year.
Stratosphere: the region of the atmosphere above the troposphere.
The stratosphere extends from about 10km to about 50km in altitude.
Commercial airlines fly in the lower stratosphere. The stratosphere
gets warmer at higher altitudes. In fact, this warming is caused
by ozone absorbing ultraviolet radiation. Warm air remains in
the upper stratosphere, and cool air remains lower, so there is
much less vertical mixing in this region than in the troposphere.
Troposphere: the region of the atmosphere closest to the
Earth.
The troposphere extends from the surface up to about 10 km in
altitude, although this height varies with latitude. Almost all
weather takes place in the troposphere. Mt. Everest, the highest
mountain on Earth, is only 8.8 km high. Temperatures decrease
with altitude in the troposphere. As warm air rises, it cools,
falling back to Earth. This process, known as convection, means
there are huge air movements that mix the troposphere very efficiently.
UV: ultraviolet radiation.
Ultraviolet radiation is a portion of the electromagnetic spectrum
with wavelengths shorter than visible light. The sun produces
UV, which is commonly split into three bands: UVA,
UVB, and UVC. UVA is not
absorbed by ozone. UVB is mostly absorbed
by ozone, although some reaches the Earth under normal conditions
and even more will reach the surface because of ozone
depletion. UVC is completely absorbed by ozone and normal
oxygen (O2). NASA provides more information on their
web site.
UVA: a band of ultraviolet radiation with wavelengths from
320-400 nanometers produced by the Sun.
UVA is not absorbed by ozone. This band
of radiation has wavelengths just shorter than visible violet
light. NASA provides more information on their
web site.
UVB: a band of ultraviolet radiation with
wavelengths from 280-320 nanometers produced by
the Sun.
UVB is a kind of ultraviolet light from the sun (and sun lamps)
that has several harmful effects.
It is particularly effective at damaging DNA, causing melanoma
and other types of skin cancer. It has also been linked to damage
to some materials, crops, and marine organisms. The ozone
layer protects the Earth against most UVB coming from the
sun. It is always important to protect oneself against UVB, even
in the absence of ozone depletion, by wearing
hats, sunglasses, and sunscreen. However, these precautions will
become more important as ozone depletion worsens. NASA provides
more information on their
web site.
UVC: a band of ultraviolet radiation with wavelengths shorter
than 280 nanometers.
UVC is extremely dangerous, but it is completely absorbed by
ozone and normal oxygen (O2). NASA provides
more information on their
web site.
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