United States Office of Research and EPA/640/K-95/004
Environmental Protection Development March 1995
Agency Washington, DC 20460
Stratospheric
Ozone Depletion
A Focus on EPA's
Research
-------
EPA's Office of Research and Development
The Office of Research and Development (ORD)
conducts an integrated program of scientific research
and development on the sources, transport and fate
processes, monitoring, control, and assessment of risk
and effects of environmental pollutants. These activi-
ties are implemented through its headquarters offices,
technical support offices, and twelve research labora-
tories distributed across the country. The research
focuses on key scientific and technical issues to
generate knowledge supporting sound decisions
today, and to anticipate the complex challenges of
tomorrow. With a strong, forward-looking research
program, less expensive more effective solutions can
be pursued and irreversible damage to the environ-
ment can be prevented.
-------
"It is important to recognize that by the time it
is possible to detect decreases in ozone
concentrations with a high degree of confidence,
it may be too late to institute corrective
measures that would reverse this trend."
(U.S. EPA's Science Advisory Board, March, 1987)
In September of 1987 the United
States, along with 26 other countries,
signed a landmark treaty to limit and
subsequently, through revisions,
phase out the production of all sig-
nificant ozone depleting substances.
Many researchers suspected that
these chemicals, especially chlorof-
luorocarbons (CFCs) and halons,
were depleting the protective strato-
spheric ozone layer and allowing
increased levels of solar radiation to
reach the Earth's surface. What made
this treaty the Montreal Protocol
on Substances that Deplete the
Ozone Layer so significant is that
consensus was reached and action
taken based upon scientific theory.
Although the causes and effects of
stratospheric ozone depletion are still
not completely understood, these
countries (joined by 106 more as of
1994) agreed that the potential risks
were significant and that environ-
mentally safe alternatives to ozone
depleting substances (ODSs) could
be developed.
The Protocol was not ratified
without considerable debate. One
significant concern was that eco-
nomic alternatives would be difficult
to find. The highly-engineered com-
pounds in question included
refrigerants (refrigerators and freez-
ers), coolants (air conditioning),
synthetic foams (insulation, life
vests, pads), propellants (aerosol
spray cans), cleaning solvents, fire
extinguishers, and sterilizers. Typi-
cally, these compounds were
nonflammable, noncorrosive, non-
reactive, low in toxicity and efficient
in heat absorption and transfer ... a
vital combination of traits consider-
ing their applications. Would use of
alternatives present an even greater
threat to human health and the envi-
ronment? Would alternative
compounds require replacement or
expensive conversion of current
equipment? Would developing na-
tions be provided the necessary
technology and financial assistance
to accommodate the phaseout? Were
fluctuations in the stratospheric
ozone layer simply natural phenom-
ena?
As asserted by EPA's Science
Advisory Board several months prior
to Protocol ratification, delaying glo-
bal action until every facet of the
ozone depletion issue was com-
The stratospheric
ozone layer should
heal through
reduced emissions
of ozone depleting
substances.
However, due to the
long life span of
these chemicals
and their gradual
migration to the
stratosphere, we
have yet to face the
time of greatest
solar radiation
levels and the
potential
consequences.
Printed on Recycled Paper
-------
90% of the ozone
present in the
Earth's atmosphere
can be found in the
stratosphere. This
stratospheric
ozone is considered
to be beneficial
because of its ability
to screen out
potentially harmful
solar radiation. Much
of this ozone is
created over the
equator (where the
sun's rays are most
direct) and is
transported by global
air currents toward
the poles.
Tropospheric
ozone is a
component of smog
- and quite often
part of the air we
breathe. This
harmful "layer" of
ozone, formed when
sunlight reacts with
certain pollutants,
can damage lung
tissues, crops and
other plants.
pletely understood might have al-
lowed irreparable damage to the
stratospheric ozone layer. Strategies
to effect the phaseout as mandated
by the Protocol were devised and key
areas of needed research and devel-
opment were identified.
Amendments to both the Montreal
Protocol (1990 and 1992) and in the
U.S., the Clean Air Act (1990), have
further accelerated the phaseout
schedule.
The mission of EPA's Office of
Research and Development (ORD)
includes identifying and quantifying
the risks associated with strato-
spheric ozone depletion; working
cooperatively with the private sector
to catalyze development of safe al-
ternative chemicals and
technologies; and studying both
natural and human-induced effects
on the Earth's atmosphere. Through
an orderly phaseout of ozone deplet-
ing substances and a thorough
understanding of the potential effects
of increasing levels of solar radia-
tion, policy makers and citizens alike
can remain aware of the risks while
effecting solutions to the problem.
Understanding Ozone and
the Atmosphere
As seen in the diagram below,
the Earth's atmosphere consists of
four layers (listed respectively from
closest to furthest away from the
Earth's surface): troposphere, strato-
sphere, mesosphere, and
thermosphere. Regions between each
of these layers where temperature
remains constant (isothermal) tend to
reduce mixing between layers. How-
ever, since temperature in the
troposphere (where our weather oc-
curs) normally decreases with
increasing height, a great deal of tur-
bulence occurs. This turbulence and
instability allows upward movement
of air currents that may contain the
heavier-than-air ozone depleting sub-
stances. While ozone can be found in
the troposphere as a chief component
of smog (see box at left), a great deal
of effort is being devoted to reduc-
tion of this "ground-based" ozone.
The next layer stratosphere
is much more stable than the tropo-
sphere and has little influence on the
weather. The stratosphere does, how-
Note: Relative scale
pictured is not
accurate. The
average radius of
the Earth is
approximately
3,959 miles.
&..
-------
ever, contain high levels of ozone
gas (referred to as the "ozone layer")
that absorb much of the sun's ultra-
violet radiation (including
ultraviolet-B a type of solar radia-
tion that has been linked to skin
cancer, eye disease, immune system
disorders, and damage to various ma-
rine and terrestrial ecosystems).
Since the outer two layers (mesos-
phere and thermosphere) have much
lower concentrations of ozone (and
other atmospheric components), they
do not significantly affect the incom-
ing ultraviolet radiation.
Ozone (O3) molecules are made
up of three oxygen atoms while the
diatomic oxygen molecules we need
to breathe consist of only two oxy-
gen atoms (O2). Ozone molecules are
created and broken down continu-
ously in our atmosphere.. .essentially
maintaining a balanced oxygen to
ozone budget.
Ozone concentration is a balance
of processes that produce ozone and
those processes and reactions that
remove ozone. Natural formation of
stratospheric ozone involves two
steps: 1) the sun's rays strike and
According to NASA,
of the incoming short-
wave solar radiation,
only 50% hits the
Earth's surface24%
as direct sunlight and
26% as scattered
sunlight. The rest of
the incoming short-
wave radiation gets
caught up in the
Earth's atmosphere,
where it is either
scattered back into
space (25%) or
simply absorbed
(25%).
Natural Ozone Production in the Stratosphere
Ultraviolet radiation from
the sun strikes a diatomic
oxygen molecule and
splits it into two
oxygen atoms.
Diatomic oxygen
molecule
Oxygen
atoms
The free oxygen atoms react
with diatomic oxygen molecules
to form ozone.
Ozone
molecule
Natural Ozone Destruction in the Stratosphere
Ozone absorbs ultraviolet light in the range of
290-320 nanometers. This solar energy
breaks apart the ozone molecules
into diatomic oxygen /\
molecules and ,^ /
oxygen atoms. /
Oxygen
atom
The free oxygen atom can react with an
ozone molecule and form two molecules
of diatomic oxygen.
Ozone
molecule
Diatomic oxygen
molecules
-------
Ozone Destruction Caused by Manmade Compounds (e.g., CFCs)
Ultraviolet radiation from
the sun strikes the CFC
molecule and causes a
chlorine atom to break
away.
Fluorine
Chlorine
Chlorofluorocarbon
(CFC) molecule
The chlorine atom reacts with
an ozone molecule to form
chlorine monoxide and
diatomic oxygen.
Chlorine
atom
Ozone molecule
made up of3
oxygen atoms
Chlorine
monoxide
Diatomic
oxygen
When a free atom of oxygen
reacts with a chlorine monoxide
molecule, diatomic oxygen is
formed and the chlorine atom
is released to destroy more
Oxygen
atom
Chlorine
monoxide
Diatomic
oxygen
Chlorine
atom
-------
split apart oxygen molecules (O2)
into single oxygen atoms (O); 2)
these single atoms are very unstable
and will react readily with nearby
atoms or molecules to become more
stable. When O atoms combine with
nearby O2 molecules, ozone is
formed.
Stratospheric ozone levels fluc-
tuate periodically. Under some
circumstances, the fluctuations are
extreme. For instance, atmospheric
conditions can at times isolate a por-
tion of the stratosphere . . .
effectively keeping it from mixing
with surrounding ozone-rich and
warmer pockets of air. Should there
be a high concentration of ozone de-
pleting substances in the isolated
pocket, ozone destruction can out-
pace ozone replacement and result in
a sharp decrease in ozone concentra-
tion (an "ozone hole") and
consequently, less screening out of
the sun's ultraviolet-B rays.
This extreme depletion occurs
during the southern spring (Septem-
ber through November). . .
creating the Antarctic "ozone hole."
Atmospheric conditions there clearly
favor the annual phenomenon (ex-
tremely cold winter temperatures
support the formation of a "polar
vortex" an impenetrable core in
the atmosphere) where ozone deplet-
ing substances accumulated
throughout the winter can be acti-
vated by springtime solar radiation to
October mean
concentrations of
ozone in the
stratosphere over
Antarctica during
the years 1991 to
1994. Reds and
greens indicate high
ozone
concentrations
while blues and
purples indicate low
ozone
concentrations (see
color index). The
"ozone hole"
typically breaks up
in mid-November.
-------
Concentrations of
ozone depleting
substances in the
stratosphere are not
expected to peak
until the year 2000.
Monthly mean
measurement
curves of CFC-11
and CFC-12 from 7
monitoring sites for
the period from
1977 to 1993
(adapted with
permission from
Elkinsetal., 1993).
break down ozone. Additionally, ice
crystals present in this region of the
stratosphere act as reaction "plat-
forms" for enhanced ozone
breakdown.
The stable ozone depleting sub-
stances don't just destroy one ozone
molecule; a chain reaction occurs.
Using chlorofluorocarbons (CFCs)
as an example, solar radiation breaks
down the CFCs which in turn re-
leases chlorine atoms. A series of
reactions takes place, with chlorine
acting as a catalyst, that results in
destruction of ozone (O3) and the
formation of diatomic oxygen (O2).
The chlorine from the CFCs is avail-
able to begin the ozone destruction
cycle again.
Antarctic Ozone Deficit:
Why Should We Care?
Even knowing that the Antarctic
ozone hole has gotten larger since
1979, most people might not be con-
cerned. After all, few people live in
the Antarctic (e.g., international sci-
entific teams); additionally,
shouldn't decreasing CFC produc-
tion eventually shrink the ozone hole
to its natural size?
Recent findings (Elkins et al.,
1993) do indicate that the increasing
rate of emissions of two significant
ozone depleters (CFC-11 and CFC-
12) has slowed (see figure below).
EPA's Office of Air and Radiation
has successfully implemented regu-
c
g
2
"c
-------
How EVERYONE CAN HELP
Car Air Conditioning
Have your car air conditioning system
properly serviced. Only certified technicians
using approved recovery or recycling
equipment may work on car air conditioners.
Ask your service company if its technicians
and equipment meet EPA requirements
before agreeing to service.
Check for leaks. Have leaks repaired before
more refrigerant is
added. Some states may
require this by law.
Ask about retrofitting.
Many of today's car air-
conditioning systems will
soon be able to use an
alternative refrigerant
that does not destroy
ozone.
Old Refrigerators
and other Appliances
Dispose of appliances
responsibly. CFC or
HCFC refrigerant must
be removed from an
appliance before it is
discarded. The public
works or solid waste
department in your town
or a home appliance
dealer can help. Ask
about home appliance
recycling or CFC recovery programs.
Help start a refrigerant recovery and
recycling program in your area. Contact
EPA's Stratospheric Ozone Information
Hotline to hear about innovative steps some
communities have already taken. The
number is 800-296-1996.
The New Clean Air Act
The Clean Air Act of 1990 contains
many measures to protect the ozone
layer. Most important, the law
requires an end to the production of
chemicals that deplete the ozone
layer. CFCs will not be produced
after 1995. HCFCs can replace CFCs
in some air conditioning systems and
may be produced until 2030.
Home Air Conditioners
Ensure that refrigerant is recovered. The
intentional release or "venting" of refrigerant
during service, maintenance, and disposal is
prohibited. Used refrigerant can be recycled.
Before agreeing to service, ask whether the
technician will use refrigerant-recovery
equipment if the refrigerant needs to be
removed. Also, ask if the technician is or
plans to become certified by an EPA-
approved organization.
After the job has been
completed, ask if the
equipment was used.
In addition, the Clean Air Act bans
the release of CFC and HCFC
refrigerants during the service,
maintenance, and disposal of air
conditioners (and all other equipment
that contains these refrigerants).
Individuals who work on such
equipment must follow EPA
regulations for ozone-safe service
practices, including the recovery and
recycling of refrigerant.
Repair leaks. Ask the
service technician to
locate and repair leaks
before refilling (or
"recharging") your
system with more
refrigerant.
Violation Reports
Call the Hotline. If you
suspect or witness
unlawful refrigerant
releases, you can file a
report easily and
anonymously by calling
the Stratospheric Ozone
Information Hotline at
800-296-1996.
Other Actions
Become active in your community. Speak
with your neighbors and friends about ozone
depletion and their air conditioners.
Be an informed consumer. Look for labels
identifying products manufactured with or
containing ozone-depleting substances.
Consider alternatives that do not damage the
ozone layer.
(Adapted from the publication EPA/430/F-93/006)
-------
Ultraviolet Region of the
Electromagnetic Spectrum
0 200 295 320 400
Wavelength in Nanometers (one-billionth of a meter)
Energy is transferred from the sun to the earth in the form of
electromagnetic energy. Electromagnetic energy can be
divided into a spectrum, in which photons that transfer energy
have both a wavelength and energy level. The electromagnetic
spectrum is divided into ultraviolet, visible, and infrared regions.
The ultraviolet (UV) region, shown above, is composed of
UV-C, UV-B, and UV-A. Ozone differentially removes
wavelengths of UV-B between 295 and 320 nm; UV-A in
wavelengths above 350 nm is not removed, nor is visible light
(400-900 nm). Ozone removes all UV-C. Wavelengths between
295 and 300 nm are generally more biologically effective (i.e.,
able to cause damage) than other wavelengths in UV-B and
even more so than UV-A radiation.
(Adapted from the publication EPA/400/1-87/001D)
lations (under Title VI of the
amended Clean Air Act) limiting
production, sales and imports of
these and other ozone-depleters. Ad-
ditionally, standards and
requirements regarding servicing air
conditioners and recycling refriger-
ants are now in place in the U.S. (see
available publications listed on page
23).
Given the stability of the ozone
depleting substances already in the
atmosphere, the continued (yet de-
creased) release of these substances,
and the anticipated emissions of tem-
porary alternatives (that deplete
ozone to a lesser extent), most scien-
tists believe that the lowest levels of
worldwide stratospheric ozone (and
the greatest potential effects of UV
radiation exposure) are yet to come.
Interest Rises in S. America
In some countries, potential ad-
verse consequences do exist as a
result of localized ozone depletion
over Antarctica. Argentina, Chile, S.
Africa, and New Zealand are threat-
ened annually by the Antarctic ozone
hole. During September and October
of 1991, the Antarctic ozone hole al-
lowed a large human population in
the southern tip of South America to
be exposed to increased levels of
UV-B. The affected location with the
greatest population density was the
city of Punta Arenas in southern
Chile (110,000 inhabitants). In re-
An international team of scientists was sent to Punta Arenas,
Chile, to investigate reports of human and animal health problems
associated with regional stratospheric ozone depletion.
-------
sponse to numerous reports from that
region of acute (i.e., damage caused
by a short-term exposure) eye and
skin disease in both humans and ani-
mals, ORD's Health Effects
Research Laboratory joined a
multidisciplinary international team
to investigate these reports in No-
vember of 1992 (that month was
purposefully chosen to capture any
effects of similar ozone depletion in
September and October of that year).
Human Health Findings
Though UV-B exposure in-
creased in the vicinity of Punta
Arenas by approximately nine per-
cent in September and four percent
in October, a review of area medical
records showed no associated in-
crease in reports of eye disease or
skin irritation. A greater frequency of
dermatologic visits for warts did oc-
cur yet the significance of this
finding remains uncertain.
Three occupational groups (fish-
ermen, shepherds, and hospital
workers) were given standard eye
and skin exams to discover if any
trends could be related to the amount
of time spent outdoors. No health
differences by occupational category
could be associated with increased
UV-B exposure.
Animal Health Findings
Eye exams of sheep from the
Punta Arenas region revealed an ab-
normally high rate of infection
caused by the microorganism
Chlamydia psittaci. However, no
known relationship exists between
this infection and solar exposure. A
13 percent rate of cataract was found
in the studied sheep but comparison
statistics for the breed of sheep com-
mon to the region do not exist. In a
small sample of Hereford cattle, the
team found a 17 percent incidence of
Ozone
destruction
Stratospheric ozone
prevents a major
proportion of
ultraviolet rays from
degrading stable
ozone depleting
substances in the
lower atmosphere.
However, once
ozone depleting
substances reach
the upper
stratosphere,
sufficient UV
radiation is present
to release the
atoms (e.g.,
chlorine or bromine)
that can lead to the
cycle of ozone
destruction
described in the
figure on page 4.
Stratospheric
ozone layer
Key
Ozone depleting
substances
Ultraviolet
radiation
Chlorine
atoms
-------
Viewing the Earth from the South Pole, it is easy to see why
residents ofS. America, Africa, Australia, and New Zealand are
interested in the gradual expansion of the annual Antarctic
ozone hole. At the end of each southern spring as polar
temperatures increase and the ozone hole breaks up, large
segments of ozone-deficient atmosphere can migrate over
heavily populated areas before dispersing completely.
In describing
disease and
physical disorders,
the term "acute"
refers to effects
caused by a single
or short-term
elevated exposure.
Effects resulting
from constant or
long-term exposure
are considered to
be "chronic." As an
example, sunburn
may be considered
an acute effect of
solar radiation while
certain types of skin
cancer are potential
chronic effects.
conjunctival squamous cell carci-
noma an eye condition related to
long-term UV-B exposure.
Recommendations
The Punta Arenas investigation
demonstrated the feasibility of per-
forming standardized field
examinations and using local medi-
cal records to assess the possibility
of acute UV-B related disorders.
While documented evidence of such
disorders in this region was sparse,
the relatively small sample sizes
studied made trend determinations
difficult. No changes to the Chilean
Ministry of Health's current UV-B
exposure strategy (which includes
public education and the recommen-
dation of hat and sunglass use during
periods of maximal exposure) were
recommended.
Should the exposure in this re-
gion remain constant or decrease
from the exposure levels experienced
in 1992, the team agreed that the
likelihood of acute ozone hole-re-
lated disease is low. However,
should exposures increase over the
coming years, the likelihood of
chronic UV-B related health effects
would increase.
Taxing the Food Chain
In an ecosystem (the interacting
system of a biological community
within its environment) such as the
Antarctic Ocean, plants and animals
have adapted to the harsh environ-
mental conditions. As is often the
case, these species are greatly depen-
dent upon one another for survival
(see diagram on page 12). Adverse
effects to one species in a food web
may cause harmful effects to other
species and the ecosystem as a
whole.
Though injurious UV-B effects
have been documented on some indi-
vidual species within marine
ecosystems, the nature and extent of
ecosystem responses to UV stress are
not well understood. Is the structure
and function of the total marine eco-
system more or less sensitive than its
components? Will negative effects
(e.g., increased UV-B) on the base of
the food web cascade through the
system and reduce fish production?
To answer these questions,
ORD's Pacific Ecosystem Branch
based in Newport, Oregon, is study-
ing a broad range of potential effects
related to stratospheric ozone deple-
tion and the subsequent increased
UV-B at the Earth's surface. Because
phytoplankton circulate in the eu-
photic zone (area of light
penetration) of oceans where some
-------
The Oceanic Carbon Cycle
UV-B penetrates, they are the marine
species most at risk from ozone
depletion.
Under one project, university
and EPA scientists are studying the
effects of UV-B radiation on marine
ecosystems using 13,000 liter tanks
as "living models" of a marine eco-
system. A set of these tanks will be
exposed to a range of UV-B doses,
with the effects on both primary pro-
ducers (i.e., phytoplankton) and fish
larvae determined. The results will
be incorporated into a model of UV-
B radiation effects on marine food
webs and ecosystems.
Evaluating Phytoplankton
Perhaps differences in UV-B tol-
erances between species will be great
enough to create a competitive ad-
vantage for one particular species
over another. What if animals depen-
dent upon a certain species of
phytoplankton for food cannot
readily adapt to feeding on other spe-
cies? Will more and more species in
the food web also decline? How will
decreased or different, more UV-tol-
erant phytoplankton populations
affect the carbon cycle and global
climate change (see boxes above)?
Global Climate Change: Connected to
Stratospheric Ozone Depletion
Energy from the sun passes through the Earth's atmosphere
relatively freely. However, the radiant heat emitted by the
Earth is absorbed to some degree by gases in the
atmosphere. When the concentration of these heat-absorbing
gases increases, more heat is absorbed at the Earth's surface
and the climate warms. Carbon dioxide (CO2), a key heat-
absorbing compound in the atmosphere, is used up by plants
and phytoplankton during photosynthesis. Significant
reductions in plant and phytoplankton populations due to
increased levels ofultraviolet-B radiation can be expected to
worsen the global warming phenomenon.
Many ozone depleting substances and proposed alternatives
are global warming substances. Researchers are going to
great lengths to find substitutes that minimize adverse
environmental impact.
The Pacific Ecosystem Branch is
studying the direct effects of UV-B
radiation on long-term growth and
metabolism in representative phy-
toplankton species. The research
results will aid development of mod-
els to predict the effects of increased
UV-B radiation on the structure and
function of marine phytoplankton
communities.
In a related project, growth rings
in the shells of long-lived Antarctic
bivalves (e.g., clams) are being stud-
ied much like the rings in
Plankton, forming the basis of aquatic
food chains, are microscopic life
forms inhabiting bodies of water.
Zooplankton form the animal
complement of the plankton
community. Phytoplankton, the
plant (photosynthetic) component
of this community, reside most often
near the surface where the presence
of sunlight allows photosynthesis. In this
process, phytoplankton build new organic
matter (and release oxygen) using such
components as carbon dioxide, water, and
salts. The phytoplankton at left has many small
green chromatophores and the red stigma a light-
sensitive pigment.
-------
A representation of the Antarctic marine food web. EPA's researchers are studying the effects of
increased levels ofultraviolet-B radiation on the base of this chain and how subgroup population changes
affect other organisms within this ecosystem (Source: Ambio Vol. 19, No. 2, 1990, p. 57).
-------
cross-sections of trees. Fluctuations
in growth ring sizes of these filter
feeders (i.e., they filter phytoplank-
ton out of water for food) may
correlate well with the annual Ant-
arctic ozone hole (first documented
in 1979). If so, bivalve growth rings
could be used as indicators of phy-
toplankton population reductions
resulting from stratospheric ozone
depletion.
How sensitive are phytoplankton
species to changes in solar radiation?
ORD scientists are studying phy-
toplankton pigment reactions to
increased UV-B exposure. Should a
measurable correlation be estab-
lished, pigment change can be used
as a cost-effective, ecologically rel-
evant indicator of the extent of
exposure and damage to phytoplank-
ton.
Global Ozone Deficit
The extensive Antarctic scien-
tific efforts are well established and
have been generating a broad range
of data sets for years. Over time,
ozone depletion trends have been
recognized there and the conse-
quences are being thoroughly
investigated.
The polar regions are extremely
cold for good reasonsolar radia-
tion is at its greatest angle of
incidence (i.e., least direct) at these
points and must penetrate more at-
mosphere. However, in more
temperate (and populated) areas of
the world, the sun's rays are more
direct and intense. Even so, factors
such as latitude, altitude, pollution
and cloud cover can significantly af-
fect the relative risks of UV-B
radiation.
The results of a monitoring ef-
fort in Canada (Kerr and McElroy,
1993) demonstrate that UV-B expo-
sures at the Earth's surface increased
seasonally between 1989 and 1993
(more so in winter than in summer
months). While Kerr and McElroy
note that such short-term trends
should not be used to predict future
UV-B conditions, for the first time in
North America increased levels of
ground-based UV-B energy (at a
wavelength of 300 nanometers) have
been linked scientifically to strato-
spheric ozone depletion. Ongoing
EPA effects research will provide
data needed to determine the relative
risks of increased UV-B exposure
and whether changes in stratospheric
ozone significantly affect those risks.
With this information, EPA can bet-
ter inform the public and
policymakers should adaptation
strategies against increasing UV-B
radiation become necessary.
Understanding UV-B Effects
on Humans
In response to the global threat
of increased UV-B exposure, and in
light of indicated connections of
such exposure to immune system
disorders, eye disease, and skin can-
cer, ORD's Health Effects Research
Laboratory convened an expert panel
in 1988 to recommend a research
strategy. The panel identified the fol-
lowing key questions to be answered
through EPA's human health re-
search: 1) Does immune system
suppression by UV-B exposure occur
in humans as it does in experimental
mice? 2) Does this same immune
suppression lead to enhanced suscep-
tibility to infectious diseases and
UV-induced cancers? 3) Does
greater skin pigmentation protect
against the immunosuppressive re-
sponse? 4) While sunscreens protect
against sunburn, do they also prevent
other effects associated with UV-B?
The following three sections
highlight some of ORD's research
In his book "Earth in
the Balance," Al
Gore (1992)
compared the
phenomenon of
stratospheric ozone
depletion to the
pouring of a sand
pile: "Small changes
reconfigure the
sand pile and
ultimately render it
vulnerable to larger
changes."
-------
To prevent
overexposure to
UV-B, health
officials recommend
protective clothing,
sunglasses, liberal
use of sunscreen,
and wise planning of
outdoor activities
during daylight hours.
projects aimed at better understand-
ing the human health effects of
UV-B exposure.
Connecting UV-B to Immunity
The contact sensitivity assay is a
convenient tool used to test immune
responses under various conditions.
Here, a compound (such as
dinitrochlorobenzene or DNCB) is
applied to the subject's skin. Under
normal circumstances, this initial ex-
posure results in an immune
response which on second exposure
to the same agent results in a rash.
The rash is an expression of immune
responsiveness.
When mice or humans are ex-
posed to UV prior to the first
exposure to the agent, the immune
response does not develop and a rash
on second exposure does not occur.
Since these same types of immune
responses are needed to defend the
host against certain types of infec-
tions, the inability to make this
response suggests that the ability to
defend the host against these infec-
tions may be compromised by UV-B.
ORD's Health Effects Research
Laboratory has supported research
showing that prior exposure to UV-B
radiation enhanced several types of
infections in mice. One infection
studied leishmaniasis is a skin
disease caused by the bite of
sandflies carrying the protozoan,
Leishmania major. With simulta-
neous UV-B exposure (at
typically-encountered levels), the
sore caused by the vector's bite (usu-
ally significant due to a dermal
immune response) was smaller in
comparison to test animals not ex-
posed to UV-B. An abnormally high
concentration of live organisms
could be found at the site of the bite
and in the lymph nodes in those mice
exposed to UV-B. Additionally, the
UV-B-exposed mice failed to de-
velop protective immunity against
repeat infections.
Another interesting discovery
was made when researchers infected
test animals at one part of the body
while exposing another body part to
UV-B. The immune response was
still suppressed (leading to an abnor-
mally high spread of infection to
other parts of the body). These data
suggest that the infection does not
have to occur at the same site as the
UV-B exposure for the individual to
experience immunological suppres-
sion. It is thought that the immune
system gets programmed wrong such
that there is stimulation of a different
set of immune responses which ac-
tively suppress or reduce responses
that would ordinarily limit certain
types of infection and provide protec-
tive immunity.
Certain routine vaccinations rely
on similar protective immune re-
sponses to help people (and animals)
fend off disease. Future ORD work
in this area may provide valuable in-
sight on vaccine effectiveness after
UV-B exposure.
Screening Out UV-B
Components of various sun-
screens, though effective at
preventing sunburn, may be ineffec-
tive or even enhance the possibility
of other UV-B induced effects (e.g.,
immunosuppression). Since total
avoidance of sunlight is not feasible,
it is often assumed that sunscreens
provide the necessary protection dur-
ing times of unavoidable exposure.
Using the developed contact sen-
sitivity assay, University of Michigan
researchers under cooperative agree-
ment with EPA have recently begun
to apply various sunscreens (and sun-
screen components) prior to UV-B/
contact sensitivity tests. While results
-------
of this ongoing project are as yet un-
available, ORD's efforts may help
determine whether sunscreen use can
protect against UV-induced immune
suppression.
Does Skin Pigmentation Block
UV-B Effects?
Fair skin is more sensitive to
sunburn and skin cancer. Though
ORD's research in this area is still
underway, preliminary findings indi-
cate that pigmentation does not
completely protect an individual
from the immunosuppressive effects
of UV-B exposure. Additionally,
since people with greater skin pig-
mentation suffer less from sunburn
and are consequently less likely to
take precautions against excessive
exposure to solar radiation, they may
be at greater risk from UV-B-related
immune suppression. Information
from these studies could support the
added use of protective measures
among all races.
Monitoring UV-B Levels
Despite models and theories sug-
gesting that stratospheric ozone
depletion should lead to increases in
UV-B radiation and associated bio-
logical effects, what is actually
known about increases in UV-B in
the United States? What UV-B
wavelengths are changing because of
ozone depletion and shifts in concen-
trations of pollutants (including
tropo spheric ozone)?
ORD's Atmospheric Research
and Exposure Assessment Labora-
tory has initiated a program to
develop and operate a monitoring
network, in cooperation with other
federal and international agencies, to
determine ultraviolet radiation
changes at the Earth's surface. Data
are to be compiled from 15 sites (11
urban and 4 rural) and analyzed to
estimate the impact of various fac-
tors on UV radiation reaching the
Earth's surface.
Seattle
San
Francisco
Los Angeles
Arctic Circle Site
Miami
EPA UV-B Monitoring Sites (operational sites in yellow and proposed sites in red).
-------
Amphibians in Decline
A recent study by A.R. Blaustein etal. (Proc. Natl. Acad. Sci.,
1994), based on evidence suggesting a global environmental
cause for amphibian population decline, measured the effects
of increased UV radiation on the hatching success of several
types of frog eggs. Species not considered to be in decline had
greater hatching success when exposed to increased UVthan
species whose numbers are in decline. Additionally, the latter
group had a greater hatch rate when shielded from UV
radiation.
Photo ofEPA/IRRI
cooperative study in
the Philippines.
Irrigated rice can be
grown under a
number of stressed
conditions (including
increasing UV-B
radiation) to
demonstrate
potential effects of a
thinning
stratospheric ozone
layer on growth and
productivity of rice.
Informing the Public
How does EPA make the public
aware of the effects of excessive ex-
posure to UV radiation? EPA's
Office of Research and Develop-
ment and its Office of Air and
Radiation, in cooperation with the
National Weather Service, is raising
public awareness of exposure to UV
through the daily publication of a
predictive UV "Exposure Index."
The "Index," similar to the one de-
veloped in Canada in 1992, employs
stratospheric ozone values derived
from a National Oceanic and Atmo-
spheric Administration satellite.
Provided along with the daily
weather report, the "Index" estimates
the maximum expected UV dosage
for one hour centered around solar
noon. Accompanying this daily value
are the associated risks for various
skin types affording individuals at
risk a chance to take precautions
(e.g., hats, sunglasses, sun screen) as
needed. The "Index" will be vali-
dated and further refined to include
results from EPA's ground-based
monitoring network once it is opera-
tional and the data have been
analyzed.
The monitoring network will
also be used to assess and improve
the models for predicting the UV
flux (i.e., variations in UV penetra-
tion) accounting for pollutants and
other factors. Such model validation
requires accurate measurements
throughout the U.S. as well as con-
sideration of the following
parameters: solar angle, altitude,
-------
cloud coverage and density, physical
parameters of the atmosphere, total
column ozone, nitrogen dioxide,
aerosol scattering, tropospheric
ozone, and sulfur dioxide. Rigorous
quality assurance/quality control pro-
cedures and comparisons with other
federal and international agencies
will ensure data that are compatible
with other existing monitoring net-
works.
Understanding UV-B Effects
on Crops
If global stratospheric ozone lev-
els decrease, will a critical point of
increasing UV-B penetration be
reached that causes far-reaching en-
vironmental consequences? While
human activities can be changed to
minimize the direct effects of in-
creased UV-B exposure, species of
plants and other animals may be at
great risk. Decreased food produc-
tion through crop damage is
recognized as a priority concern. Be-
cause rice is a staple food for over
half of the world's population, sig-
nificant failures of this crop could
lead to widespread starvation and se-
rious societal problems.
Are popular varieties of rice sen-
sitive to increasing levels of UV-B
and other changing climatic condi-
tions? How might climate and UV-B
levels change in rice-producing areas
D Other (25%)
China (39%)
India (19%)
n Indonesia (8%)
Bangladesh (5%)
D Thailand (4%)
Approximate rice productivity by country. Rice provides 2.7
billion people more than 70% of their calories.
Some key factors that can affect global rice production.
of Asia? Can a UV-B-resistant strain
of rice be found or bred to replace
vulnerable varieties? In 1990, EPA's
Environmental Research Laboratory
at Corvallis, Oregon began working
with the International Rice Research
Institute (IRRI) in the Philippines to
leam more about rice vulnerability to
changing global conditions. Addi-
tionally, mitigation/adaptation
options would be explored to reduce
the effect of UV-B and climate
change.
The research efforts for this
project include climate scoping stud-
ies, experimental studies, and how to
carry out assessments. Scoping stud-
ies have used modeling to produce
plausible UV-B and climate change
scenarios for the trop-
ics where the
majority of world rice
production occurs.
The experimental
studies (controlled
environment and field
studies) are being
conducted on crop
sensitivity, dose-re-
sponse relationships,
and other responses
of rice (e.g., greater
disease susceptibility)
-------
"Today, I am also
signing an
executive order that
directs federal
agencies to make
preliminary changes
in their purchasing
policies, to use
fewer substances
harmful to the
ozone layer. Here,
too, we must put
our actions where
our values are. Our
government is a
leading purchaser
of goods and
services. And it's
time to stop not only
the waste of
taxpayers' money
but the waste of our
natural resources."
Excerpt from
President Bill
Clinton's 1993 Earth
Day speech.
to increasing UV-B and global cli-
mate change (increased levels of
carbon dioxide and higher tempera-
ture). The assessment component
will develop methods to extrapolate
results from the experimental studies
to rice physiological and ecosystem
models which could be used to
estimate regional rice yield changes.
Ultimately, assessments could pro-
vide options for policymakers and
rice producers when planning future
agricultural strategies.
Developing Alternative
Chemicals and Technolo-
gies
The rapid phaseout schedule for
all ozone depleting substances has
raised concern in the U.S. and abroad
about the availability of environ-
mentally-acceptable replacements.
Although research by government
agencies and industries has identified
alternative compounds for nearly all
existing systems, extensive research
remains to be done.
Many of the current alternatives
are only interim solutions they
still deplete stratospheric ozone to
some degree (typically, the ozone
depleting potential of these alterna-
tives is only 5% in comparison to the
original compounds a lesser of
two evils) and most contribute to the
global warming phenomenon. Addi-
tionally, alternative compounds for
some small volume applications
(e.g., CFC-propelled inhalants for
asthmatics) have yet to be approved.
In searching for alternative com-
pounds and technologies, ozone
depleting potential is a chief consid-
eration. However, practicality must
also be factored in. Most people care
about the environment and long-term
health risks yet conversion to
ozone friendly alternatives must be
affordable to assure implementation
on a large scale. For some develop-
ing countries, food refrigeration
could save lives by allowing longer
storage of food with less chance of
bacterial contamination. For these
countries, expensive new ozone
friendly units might forever remain
out of reach.
Although the Montreal Protocol
will prohibit all production of ozone
depleting substances, strategies are
being explored to allow continued
use of existing equipment until it
wears out. Perhaps drop-in or near
drop-in chemical replacements might
be developed requiring little or no
equipment conversion. Also, suc-
cessful recycling programs should
ensure supplies of original com-
pounds in the interim. For new
equipment, the possibility exists that
new chemicals may be used or that
entirely new technologies may be
developed that would satisfy the
same need as the original equipment
without using the old chemicals.
ORD's Air and Energy Engi-
neering Research Laboratory
(AEERL) is pursuing a wide range of
research tasks to generate data on the
properties of new chemicals and
their performance in new and exist-
ing systems. Aiming at final (zero
stratospheric ozone depletion poten-
tial) yet practical solutions, the
Laboratory employs a standard series
of screening tests on possible re-
placement chemicals enough
testing to convince private industry
that the proposed alternative is po-
tentially worthwhile. Industry then
performs a more complete range of
tests (taking up to 3 years) on design
specific aspects, compound toxicity,
and other important end effects be-
fore trying to market a product.
AEERL testing facilities include
a properties laboratory where poten-
tial alternative chemicals and
mixtures are analyzed. Flammability,
-------
oil/refrigerant miscibility (ability to
remain mixed under various condi-
tions), and materials compatibility
are among the qualities measured
here.
In a second area, application of
potential alternatives are tested under
controlled conditions (e.g., super-
market cases, refrigerator/freezers).
Part of the task in this area of re-
search is to review various
equipment designs, new and old (in-
cluding models that never made it to
market), to see if they are somehow
more compatible with alternative
chemicals.
In a third laboratory area, an au-
tomobile simulator (a passenger car
simulator box) has been built so that
alternative air conditioning units, re-
frigerants, and conversion processes
can be evaluated. The cost of con-
verting automobile air conditioning
systems varies by make and model
year.
Applications for New
Chemicals
Chillers represent one of the pri-
mary potential uses for AEERL's
new chemicals. The most prevalent
type of air-conditioning system uses
chillers to effect cooling of the de-
sired areas or processes. In chillers,
water or a water/glycol mixture,
which has been cooled in the evapo-
rator of a vapor compression
refrigeration system, moves through
heat exchangers to cool and dehu-
midify air or to cool various
processes. Chiller life spans 10 to 40
or more years.
Among AEERL's new chemi-
cals, several HFCs
(hydrofluorocarbons) have been
identified with zero ozone-depletion
potential, low global warming poten-
tial, and suitable thermodynamic
properties for centrifugal chiller ap-
plications.
Navy Shipboard Chillers
The Navy has tentatively decided
to use one of two new refrigerants
(HFC-236ea and HFC-236fa) devel-
oped by EPA as replacements for
ozone-depleting CFC-114 currently
used in 900 shipboard chillers.
Working with AEERL and a chemi-
cal producer to conduct preliminary
evaluations, the Navy has concluded
that these two chemicals are the most
viable candidates for retrofitting ex-
isting shipboard chillers.
Based on data being obtained,
the Navy will decide which of the
two candidate EPA chemicals will be
selected for long-term toxicity test-
ing and detailed performance
evaluations. These tests are neces-
sary to justify commercial
production of the chemical, for in-
corporation of any required design
changes in the refrigeration systems,
and to ensure safe occupational ex-
posure. The tests must be completed
in time to permit fleet retrofitting to
commence in 1998.
Assuming HFC-236ea or HFC-
236fa proves acceptable, the Navy
estimates that retrofitting existing
chillers with the new refrigerant
would cost approximately $500 mil-
lion less than replacing all of the
chillers. Replacement of CFC-114 in
Navy chillers with either of the can-
didate refrigerants could also lead to
expanded use in the public refrigera-
tion sector and would speed
replacement of ozone-depleting sub-
stances.
Commercial chillers
Centrifugal water chillers are the
primary means for air conditioning
buildings encompassing over 40,000
square feet. They account for about
75 percent of the chiller-equipment
stock and over 95 percent of the CFC
emissions from chillers. They use
Once existing
ozone depleting
chemicals are
collected, they can
be dealt with in the
following ways:
1) recycling;
2) chemical
transformation;
3) destruction;
and 4) long-term
storage.
-------
Comparison photos offlammability tests performed at ORD's Air and Energy Engineering Research
Laboratory. Blends of some "ozone-friendly" alternatives are being used to reduce the flammability of
replacement compounds without significant reduction in its overall performance.
Important factors
when considering
replacement
chemicals include:
toxicity
ozone depleting
potential
global warming
potential
atmospheric
lifetime
efficiency
capacity
flammability
compatibility
with lubricants
and materials
commercial
producibility
cost
mainly CFC-11; however, CFC-12,
CFC-114, and HCFC-22 are also
used.
Among AEERL's new chemi-
cals, HFC-245ca and HFC-245fa
show promise as alternatives to CFC-
11. Currently, HCFC-123 is being
used to replace CFC-11, and CFC-12
is being replaced by HFC-134a (al-
though concern about its unfavorable
global warming potential stimulates
the search for better alternatives).
While HFC-245ca, in its pure
form, is a fitting replacement for
CFC-11, it is slightly flammable,
and, therefore a potential liability to
industrial refrigeration manufactur-
ers. AEERL has blended other
refrigerants with HFC-245ca so that
the mixture is not flammable. One
blend with about 80 percent HFC-
245ca eliminates the flammability
problem without significantly de-
grading the favorable performance
features of HFC-245ca alone.
Supermarket Refrigeration
For low-temperature systems,
AEERL has identified HFE-125 as
having the best properties for per-
forming as a non-chlorinated
refrigerant. A significant consider-
ation is that its atmospheric lifetime
is lower than industry's leading alter-
natives. This shorter lifetime should
result in a significantly lower direct
global warming potential. Recent ad-
vances in supermarket-case design
technologies have lead to the possi-
bility of using pure HFE-125 as a
refrigerant. In systems with liquid
subcooling, this pure ether is ex-
pected to have performance
capabilities similar to current CFC
refrigerants. For systems requiring a
lower boiling point, blends contain-
ing HFE-125 have been identified as
promising candidates.
At the high end of low tempera-
ture systems (e.g., unit freezers),
another AEERL candidate, HFE-
143a, has acceptable thermodynamic
characteristics, and a more energy
efficient operation than industry's
alternatives is expected. This refrig-
erant is flammable, but blends using
this compound may result in a non-
flammable refrigerant equal or better
in performance than CFC types.
Heat Pumps and Air Conditioners
Currently, no single refrigerant
performs as well as HCFC-22 in heat
pumps and air conditioners. A num-
ber of refrigerant blends, however,
have shown promise. Important fac-
tors that must be considered include:
environmental impact, capacity, effi-
ciency, flammability, compatibility
with lubricants and materials, com-
mercial producibility, and cost. The
new chemicals developed by AEERL
include several that can potentially
be used in blends with other com-
mercially available chemicals to
improve performance in refrigeration
-------
equipment. Initial modeling has been
done and is being followed by ex-
perimental testing as the new
chemicals become available in suffi-
cient quantities.
Refrigerators/Freezers
AEERL is working to find near
drop-in replacements for the CFC-12
being used in refrigerators/freezers.
With a cost-effective transition to
environmentally-friendly refriger-
ants, developing countries may
choose not to use the additional ten
years allotted them by the Montreal
Protocol to halt the use of CFCs in
refrigeration equipment. Since mil-
lions of new refrigerators will be
produced or purchased by these na-
tions over the next ten years, the
need for ozone friendly refrigerants
is urgent.
India, for example, produces
over a million refrigerators annually;
about 7.5 million presently are in
service. Costly retrofitting to non-
chlorine refrigerants would cause
severe economic hardship. Finding
near drop-in replacements that are
more energy efficient will both re-
duce equipment modification
expense and be environmentally ad-
vantageous.
The leading candidate for new
refrigerator/freezers is HFC-134a.
However, since HFC-134a has sub-
stantial global warming potential and
may ultimately need to be replaced,
other compounds are being evaluated
by AEERL as potential long-term
replacements.
Foam blowing
Efforts to replace CFC blowing
agents in foam insulation products
have resulted in the development of
drop-in HCFC substitutes. While
these substitutes exhibit significantly
lower ozone depletion potential than
CFCs, they can still only serve as in-
terim replacements that must be
phased out. Ongoing AEERL re-
search has identified and categorized
a large group of novel compounds as
candidates for CFC substitutes. As a
result of this effort, several new
chemicals identified by AEERL
(HFCs -236ea, -245ca, and -245fa)
were recommended as new potential
foam blowing agents and are being
investigated further.
Insulation
To support the implementation
of alternative refrigerants (some with
lower cooling efficiencies), AEERL
has focused considerable effort on
development of insulation materials.
Working cooperatively with the De-
partment of Energy's national
laboratories, incorporation of a poly-
mer outer shell material into the
design of refrigerator/freezer doors
has shown promise in boosting insu-
lation value.
Motor Vehicle Air Conditioning
Motor vehicle air conditioning
represents one of the largest sources
of ozone-depleting refrigerant emis-
sions. AEERL's new chemicals will
be evaluated as long-term replace-
ments because, as mentioned earlier,
HFC-134a may be acceptable only in
the interim.
Incineration of Ozone
Depleting Substances
EPA research has led to widely
accepted recovery/recycling tech-
nologies for refrigerants (e.g.,
automobile air conditioners, refrig-
erators). As ozone depleting
substances are phased out, however,
the need for an ultimate means of
disposal for the remaining supplies
becomes more of a concern. In
studying incineration as a possible
A "drop-in"
replacement
chemical is one that
requires no
conversion or
redesign of existing
equipment.
-------
EPA's research has
provided U.S.
industry with a
significant head
start in developing
and ultimately
marketing new
replacement
chemicals.
means of disposal of these com-
pounds, AEERL has been carefully
monitoring the "products of incom-
plete combustion" or PICs resulting
from the process.
In a small-scale study, the scien-
tists incinerated two widely-used
types of CFC refrigerants (CFC-11
and CFC-12), and analyzed the PIC
emissions. A wide variety of PICs
were found - including dioxins and
furans.
Further testing is underway to
optimize the incineration process so
that such PICs can be avoided.
Modifications being investigated in-
clude the injection of steam into the
incinerator's flame zone as well as
altering the temperature of the incin-
erator.
Conclusion
Progress has been made in re-
ducing emissions of the greatest
depleters of stratospheric ozone. The
peak atmospheric concentration of
these substances (chiefly CFCs) is
not expected to be reached, however,
until the end of this century. Should
phaseout progress continue, a slow
decline of ozone depleting sub-
stances in the atmosphere will occur
thereafter. Though intermediate al-
ternatives deplete ozone less, they
continue to contribute to that prob-
lem as well as to the global warming
phenomenon. For many applications,
the final replacement chemicals have
not yet been found.
EPA is committed to the task of
finding ultimate solutions to the is-
sue of stratospheric ozone depletion.
Through its diverse research pro-
grams, the human health and
ecologic effects attributable to in-
creased UV-B radiation will be
identified; UV-B radiation levels
reaching the earth's surface will be
monitored and reported to enable in-
dividuals at greatest risk a chance to
take protective measures as needed.
Cooperation from industry, private
citizens, government, academia, and
the international scientific commu-
nity will ensure that alternative
compounds and technologies are de-
veloped as quickly as possible and
put to use as economically as pos-
sible.
In response to an alarm sounded
by a few scientists two decades ago,
the world has taken action to identify
the causes and effects of a major en-
vironmental problem and is moving
to solve it. With rising optimism, the
work continues.
-------
EPA Publications
The EPA publications listed below provide more detailed information on the subjects
discussed in this document. These references and additional copies of this brochure can be
requested at no charge (while supplies are available) from EPA's Center for Environmental
Research Information (CERI) by calling 513-569-7562 or by fax at 513-569-7566. Once the
CERI inventory is exhausted, clients will be directed to the National Technical Information
Service (NTIS) where documents can be purchased.
Advanced insulation for refrigerator/freezers: The potential for new shell designs incorporat-
ing polymer barrier construction, EPA/600/SR-93/009.
Effects of UV-B and global climate change on rice, EPA/600/R-93/128.
Experimental investigation of PIC formation in CFC incineration, EPA/600/SR-93/078.
Manual for non-CFC aerosol packaging: Conversion from CFC to hydrocarbon propellents,
EPA/600/S2-91/056.
Mobile air-conditioning recycling manual, EPA/600/SR-92/171.
New chemical alternatives for CFCs and HCFCs, EPA/600/F-92/012.
On the feasibility of using satellite derived data to infer surface-layer ozone concentration
patterns, EPA/600/SR-94/081.
Stratospheric ozone protection: An EPA engineering perspective, EPA/600/J-92/005.
The refrigeration research facility at the Air and Energy Engineering Research Laboratory,
EPA/600/F-92/007.
To order any of the following four publications, call EPA's Stratospheric Ozone Informa-
tion Hotline at 1-800-296-1996.
Auto air conditioners and the ozone layer: A consumer guide, EPA/430/F-93/009.
Air conditioners and the ozone layer: A checklist for citizen action, EPA/430/F-93/006.
On the trail of the missing ozone, EPA/909/K-93/001.
The Federal Experimental Ultraviolet Index: What you need to know, EPA/430/F-94/016.
-------
Cited Literature
Blaustein, A.R. etal. 1994. UV repair and resistance to solar UV-B in amphibian eggs: A linkto
population declines? Proc. Natl. Acad. Sci. USA, 91: 1791-1795.
Elkins, J.W. etal. 1993. Decrease in the growth rates of atmospheric chlorofluorocarbons 11
and 12. Nature, 364: 780-783.
Gore, Sen. Albert, Jr. 1992. Earth in the balance. New York, N.Y.: Houghton Mifflin Co.
Kerr, J.B. and C.T. McElroy. 1993. Evidence for large upward trends of ultraviolet-B radiation
linked to ozone depletion. Science, 262: 1032-1034.
U.S. EPA. 1987. Ultraviolet radiation and melanoma: with a special focus on assessing the
risks of stratospheric ozone depletion. PB88-231063.
Voytek, M.A. 1990. Addressing the biological effects of decreasing ozone in the Antarctic
environment. Ambio, 19(2): 57.
-------
This publication was prepared by Patrick Burke of ORD's Center for
Environmental Research Information. Contributors and reviewers
include Doug McKinney and Bill Rhodes of the Air and Energy
Engineering Research Laboratory; Bill Barnard of the Atmospheric
Research and Exposure Assessment Laboratory; MaryJane Belgrade
of the Health Effects Research Laboratory; Henry Lee and Anne
Sigleo of the Environmental Research Laboratory - Narragansett's
Pacific Ecosystems Branch; Dave Olszyk of the Environmental
Research Laboratory - Corvallis; Justice Manning of the Center for
Environmental Research Information; Mike Troyer of the Office of
Science, Planning, and Regulatory Evaluation; Steve Seidel, David
Lee, and Reva Rubenstein of the Stratospheric Protection Division in
EPA's Office of Air and Radiation.
------- |