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In order to understand information about ozone depletion, it is
important to know several terms and acronyms. We've listed them
below.
Aerosol:
1) small droplet or particle suspended in the atmosphere, typically
containing sulfur
Aerosols are emitted naturally (e.g., in volcanic eruptions) and as
the result of human activities (e.g., by burning fossil fuels). There
is no connection between particulate aerosols and pressurized products
also called aerosols (see below).
2) a product that relies on a pressurized gas to propel substances
out of a container
Consumer aerosol products in the US have not used ozone-depleting
substances (ODS) since the late 1970s because of voluntary switching
followed by federal regulation. The Clean Air Act and EPA regulations
further restricted the use of ODS for non-consumer products. All consumer
products, and most other aerosol products, now use propellants that
do not deplete the ozone layer, such as hydrocarbons
and compressed gases.
Carbon Tetrachloride (CCl4): a compound consisting of one carbon
atom and four chlorine atoms
Carbon tetrachloride was widely used as a raw material in many industrial
uses, including the production of CFCs, and as a solvent. Solvent
use ended when it was discovered to be carcinogenic. It is also used
as a catalyst to deliver chlorine ions to certain processes. Its ozone
depletion potential is 1.2.
Chlorofluorocarbon (CFC): a compound consisting of chlorine, fluorine,
and carbon
CFCs are very stable in the troposphere. They move to the Stratosphere
and are broken down by strong ultraviolet light, where they release
chlorine atoms that then deplete the ozone layer.
CFCs are commonly used as refrigerants, solvents, and foam blowing
agents. The most common CFCs are CFC-11, CFC-12, CFC-113, CFC-114,
and CFC-115. The ozone depletion potential (ODP)
for each CFC is, respectively, 1, 1, 0.8, 1, and 0.6. A table
of all ozone-depleting substances shows their ODPs, GWPs,
and CAS numbers. CFCs are numbered according to a standard
scheme. The National Oceanic and Atmospheric Administration provides
more detailed information about CFCs on their
web site (including graphs of their abundance in the atmosphere).
Class I Substance: one of several groups of chemicals with an
ozone-depletion potential of 0.2 or higher
Class I substances listed in the CAA include CFCs,
halons, carbon tetrachloride,
and methyl chloroform. EPA later added HBFCs
and methyl bromide to the list by regulation.
A table of class I substances shows their lifetime
ODPs, GWPs, and CAS numbers.
Class II Substance: a chemical with an ozone-depletion
potential of less than 0.2
Currently, all of the HCFCs are class II substances.
Lists
of class II substances with their ODPs, GWPs,
and CAS numbers are available.
Clean Air Act (CAA): law amended by Congress in 1990
Title VI of the CAA directs
EPA to protect the ozone layer through several regulatory and voluntary
programs. Sections within Title VI cover production of ozone-depleting
substances (ODS), the recycling and handling of
ODS, the evaluation of substitutes, and efforts to educate the public.
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.
Federal Register (FR): the daily publication containing all federal
government actions
The Federal Register is the formal method of communication for any
Notice, Notice of Proposed Rulemaking (NPRM), or Final Rulemaking
(FRM) issued by the US government. Once published in the FR, rules
are collected in the Code of Federal Regulations. The FR is available
at many libraries. FR cites ares similar in form to 11 FR 12345, where
11 is a number corresponding to the year (e.g., 62 is 1997) and 12345
represents the page number (pages are numbered continuously through
the year; the first page published in each year is page number 1).
Thus, a Notice whose cite is 62 FR 10700 was published beginning at
page 10700 in 1997. It is usually helpful to obtain the date as well,
since it is difficult to guess the date solely on the page number.
Global Warming Potential: a number that refers to the amount of
global warming caused by a substance
The GWP is the ratio of the warming caused by a substance to the warming
caused by a similar mass of carbon dioxide. Thus, the GWP of CO2 is
defined to be 1.0 . CFC-12 has a GWP of 8,500, while CFC-11 has a
GWP of 5,000. Various HCFCs and HFCs
have GWPs ranging from 93 to 12,100. Water, a substitute in numerous
end-uses, has a GWP of 0. A table of all ozone-depleting
substances shows their ODPs, GWPs, and CAS
numbers, and another table shows the
GWPs for many non-ozone-depleting substances.
Halon: a compound consisting of bromine, fluorine, and carbon
The halons are used as fire extinguishing agents, both in built-in
systems and in handheld portable fire extinguishers. Halon production
in the U.S. ended on 12/31/93 because they contribute to ozone depletion.
They cause ozone depletion because they contain
bromine. Bromine is many times more effective at destroying ozone
than chlorine. At the time the current U.S. tax code was adopted,
the ozone depletion potentials of halon 1301 and
halon 1211 were observed to be 10 and 3, respectively. These values
are used for tax calculations. Recent scientific studies, however,
indicate that the ODPs are at least 12 and 6, respectively. Note:
technically, all compounds containing carbon and fluorine and/or chlorine
are halons, but in the context of the Clean Air Act, "halon" means
a fire extinguishing agent as described above. A table
of class I substances shows their ODPs, GWPs,
and CAS numbers. Halons are numbered according to a standard
scheme.
Hydrobromofluorocarbon (HBFC): a compound consisting of hydrogen,
bromine, fluorine, and carbon
Although they were not originally regulated under the Clean Air Act,
subsequent regulation added HBFCs to the list of class
I substances. A table of class I substances
shows their ODPs, GWPs, and CAS numbers.
Hydrocarbon (HC): a compound consisting of carbon and hydrogen
Hydrocarbons include methane, ethane, propane, cyclopropane, butane,
and cyclopentane. Although they are highly flammable, HCs may offer
advantages as ODS substitutes because they are
inexpensive to produce and they have zero ozone depletion
potential, very low global warming potential
(GWP), and low toxicity. HCs are numbered according to a standard
scheme.
Hydrochlorofluorocarbon (HCFC): a compound consisting of hydrogen,
chlorine, fluorine, and carbon
The HCFCs are one class of chemicals being used to replace the CFCs.
They contain chlorine and thus deplete stratospheric ozone, but to
a much lesser extent than CFCs. HCFCs have ozone depletion
potentials (ODPs) ranging from 0.01 to 0.1. Production of HCFCs
with the highest ODPs will be phased out first, followed by other
HCFCs. A table of ozone-depleting substances
shows their ODPs, GWPs, and CAS numbers. HCFCs
are numbered according to a standard
scheme. The National Oceanic and Atmospheric Administration provides
more detailed information about HCFCs on their
web site.
Hydrofluorocarbon (HFC): a compound consisting of hydrogen, fluorine,
and carbon
The HFCs are a class of replacements for CFCs.
Because they do not contain chlorine or bromine, they do not deplete
the ozone layer. All HFCs have an ozone depletion potential
of 0. Some HFCs have high GWPs. HFCs are numbered
according to a standard scheme.
The National Oceanic and Atmospheric Administration provides more
detailed information about HFCs on their
web site.
Methyl Bromide (CH3Br): a compound consisting of carbon, hydrogen,
and bromine
Methyl Bromide's chemical formula is CH3BR. An effective pesticide,
this compound is used to fumigate soil and many agricultural products.
Because it contains bromine, it depletes stratospheric ozone and has
an ozone depletion potential of 0.6. Production
of methyl bromide will end in the U.S. on 12/31/2000. Much
more information is available.
Methyl Chloroform (CH3CCl3): a compound consisting of carbon,
hydrogen, and chlorine
Methyl chloroform is used as an industrial solvent. Its ozone
depletion potential is 0.11.
Montreal Protocol: the international treaty governing the protection
of stratospheric ozone
The Montreal Protocol on Substances That Deplete the Ozone Layer and
its amendments control the phaseout of ODS production
and use. 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
and it is part of the OzonAction
Information Clearinghouse database.
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-Depleting Substance(s) (ODS): a compound that contributes
to stratospheric ozone depletion
ODS include CFCs, HCFCs, halons,
methyl bromide, carbon tetrachloride,
and methyl chloroform. ODS are generally very stable
in the troposphere and only degrade under intense ultraviolet
light in the stratosphere. When they break down, they release
chlorine or bromine atoms, which then deplete ozone. A
detailed list of class I and class
II substances with their ODPs, GWPs,
and CAS numbers are available.
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. The science
page 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. Thus, the ODP of CFC-11
is defined to be 1.0. Other CFCs and HCFCs
have ODPs that range from 0.01 to 1.0. The halons
have ODPs ranging up to 10. Carbon tetrachloride
has an ODP of 1.2, and methyl chloroform's ODP is
0.11. HFCs have zero ODP because they do not contain
chlorine. A table of all ozone-depleting substances
shows their ODPs, GWPs, and CAS numbers,
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 ODS 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 page offers much more
detail on the science of ozone depletion.
Perfluorocarbon (PFC): a compound consisting of carbon and fluorine
PFCs have extremely high global warming potentials
(GWPs) and very long lifetimes. They do not deplete stratospheric
ozone, but EPA is concerned about their impact
on global warming.
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. UVC is completely absorbed by ozone and normal
oxygen. 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.particularly
effective at damaging DNA. It is a cause of 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. |
