Transcript Stratospheric Ozone - Oakland Community College

FSN 1500 Week 12
Stratospheric Ozone Depletion,
Ground-Level Ozone and the
Electromagnetic Spectrum
Introduction
• Although the lay press doesn’t report on
stratospheric ozone depletion like it did 5-10 years
ago, this issue is still a significant environmental
topic with global implications (see slide)
• It’s also important that you realize the difference
between stratospheric ozone (beneficial) and
ground-level ozone (detrimental)
Background
• Atmospheric scientists
partition the Earth’s
atmosphere into five
layers based on
differences in their
physical and chemical
properties; the two layers
closest to the Earth are the
troposphere and the
stratosphere (see figure)
Troposphere
• Troposphere - extends from the Earth’s
surface to an altitude of about 15 kilometers
(km); contains about 90% of all the air in
the entire atmosphere; with increasing
altitude air temperature decreases
Stratosphere
Stratosphere - extends from the
top of the troposphere to an
altitude of about 50 km;
contains about 90% of the
atmosphere’s naturally
occurring ozone; with
increasing altitude the air
temperature increases
Why does the air temperature
increase with increasing
altitude in the stratosphere?
How does stratospheric ozone
benefit life on Earth?
Stratospheric Ozone
• Stratospheric ozone benefits humans by absorbing
the bulk (~ 95%) of the ultraviolet (UV) radiation
released from the Sun
• Ozone - a pale blue, gaseous molecule composed
of three atoms (triatomic) of oxygen (O3)
• The average concentration of ozone in the
stratosphere is about 10 parts per million (ppm)
Stratospheric Ozone
• Another measure of ozone concentration is the
Dobson Unit - defined as a slab of ozone of 0.01
mm thickness that would encircle the Earth; the 10
ppm average ozone concentration is equivalent to
300 Dobson units (DU)
• If the entire stratosphere’s ozone was compressed,
a 3 millimeter (mm) thick slab of ozone would
encircle the Earth (see slide)
Stratospheric Ozone
• In reality, there is no physical ozone layer - the
ozone is distributed throughout the stratosphere
with a higher concentration found at 12 - 30 km
(commonly termed the ozone layer)
• The phrase “ozone hole” is also misleading; this
describes a volume of the stratosphere that is
markedly depleted in ozone
• Most studies now recognize an ozone hole as a
section of the stratosphere where ozone
concentrations lie below 220 Dobson units
Stratospheric Ozone
• Why discuss this topic? A significant body
of evidence suggests stratospheric ozone
levels are declining.
• Studies suggest a worldwide average
6 - 10% decline in stratospheric ozone
levels during the past three decades
• Although first recognized over Antarctica,
some degree of stratospheric ozone loss has
affected all latitudes (see figures)
South Pole
Antarctic Ozone
2010: ~21
2010: 118
Source: NASA
Stratospheric Ozone
• Be aware; this is another topic that is
frequently discussed by the news media not always correctly!
Stratospheric Ozone
• Possible consequences of
continued stratospheric ozone
depletion?
• 1) Increase in skin cancer
incidence as increased proportions
of UV light strike Earth’s surface;
the more energetic UV light can
penetrate more deeply than visible
light and could mutate skin cell
DNA
Stratospheric Ozone
• Some dose-response models
suggest a 1- 2 percent increase
in skin cancer incidence for
every 1 percent decline in
stratospheric ozone levels
• Worldwide, reported skin
cancer cases have been rising at
a faster rate than predicted
during the last 30 years. What
could be some other
contributing factors?
Stratospheric Ozone
• 2) Declines in stratospheric ozone may lead
to increases in cataracts and other eye
damage; the more energetic UV light could
also damage the eyes
• As a group optometrists are reporting a
higher occurrence frequency of the
predicted eye damage
Stratospheric Ozone
• Optometrists and ophthalmologists
recommend wearing sunglasses with 100%
UV filtration when you venture into
daylight
• How could you put yourself at further risk
for eye damage if all you wore was a pair of
dark sunglasses with no UV protection?
Stratospheric Ozone
• Eyeglasses, contact lenses, vehicle
windshields, and commercial and residential
windows now all available with UV filter
options
• 3) Declines in the autoimmune response of
humans would be expected if stratospheric
ozone levels continue to decline
Stratospheric Ozone
• Sunburn definitely lowers the concentration
and function of disease-fighting white blood
cells in the body for up to 24 hours after sun
exposure
• 4) Plant productivity projected to decline if
stratospheric ozone levels continue to
decline
Stratospheric Ozone
• The more energetic UV light can damage
plant tissue just as easily as human tissue
• 5) Indirectly, declines in stratospheric ozone
could lead to an enhanced greenhouse effect
and global warming. How? The lower the
plant productivity the less CO2 removed
from the air; the more air CO2 the more
radiated heat can be absorbed.
Stratospheric Ozone
• Studies suggest that ozone is created and
destroyed naturally in the stratosphere
according to four primary, simultaneously
occurring reactions:
• O3 (g) + UV ----> O2 (g) + O + heat
• O2 (g) + O -----> O3 (g)
• O3 (g) + O ------> 2 O2 (g)
• O2 (g) + UV -----> O + O
Stratospheric Ozone
• If the preceding reactions occur normally,
stratospheric ozone levels should have a
concentration of 300 DU
• Since the mid-1970s, evidence has
accumulated linking industrial gas
emissions to accelerated rates of
stratospheric ozone depletion
Stratospheric Ozone
• Major human impact? Apparently, the
release of chlorofluorocarbon (CFC) gases
to the atmosphere
• CFCs - a family of gases colloquially
known as freons, all of them are composed
of various numbers of chlorine, fluorine,
and carbon atoms bonded together (see
figure)
Stratospheric Ozone
• The CFCs were first produced in large
volumes by Dupont chemists in the mid
1930s as a substitute refrigeration gas for
the toxic chloromethane and ammonia gases
that were used in very small scale at that
time
• The CFCs are a perfect refrigeration gas
because they’re nontoxic, noncorrosive and
highly chemically unreactive
Stratospheric Ozone
• The primary use of CFCs have always been
as a refrigerant gas; their wide-scale
implementation allowed the US to dominate
the world’s economy for close to 50 years
• When CFCs escape from a refrigeration
unit, they rise (less dense than air or carried
upwards by air currents) toward the
stratosphere with virtually no reactivity
Stratospheric Ozone
• Laboratory studies suggest it commonly takes one
to two (perhaps as long as ten) years for CFCs to
rise to the stratosphere and that some of them may
have residence times in the troposphere from 25 –
400 years!
• When the CFCs reach the stratosphere they react
with UV light according to the reaction: CFCs +
UV ---> Cl + F + C
Stratospheric Ozone
• Apparently it’s the freed Cl and F atoms
that disrupt the natural ozone cycle
• How? Cl + O3 ---> ClO + O2 (destroys
ozone) and ClO + O ---> Cl + O2 (releases
more free Cl)
• These two reactions occur more quickly
than the four natural reactions we examined
earlier (see slide)
CFCs in Ozone Destruction
Source: Images courtesy NASA.
Stratospheric Ozone
• Lab studies suggest that one Cl atom may
destroy as many as 100,000 ozone
molecules before it’s naturally purged
• These same studies suggest a batch of
CFCs could facilitate ozone depletion for
75 - 100 years!
Stratospheric Ozone
• Predicted outcome? Stratospheric ozone
levels would continue to deplete
• The evidence accumulated in the late 1970s
and 1980s sparked action via the signing of
the Montreal Protocol in 1987 by 43, almost
exclusively Western Hemisphere, countries
Stratospheric Ozone
• The signatories agreed to reduce CFC production
to one-half their current levels by the end of 1999
• Many less technologically advanced countries
(China, India, the USSR) resisted signing, arguing
that their minor emissions of CFCs didn’t cause
the problem and that they had the right to acquire
the West’s living standards
Stratospheric Ozone
• By 1990, more data led to revision of the Montreal
Protocol - over 100 nations (exceptions being
China, India, Russia) agreed to cease CFC
production by the end of 1996 with some
exceptions for developing nations
• Later that year an international monetary fund was
created to try to lure other countries to sign the
agreement
Stratospheric Ozone
• Countries signing the agreement would be given
grant monies to research CFC alternatives
• In 1992 the Montreal Protocol was again amended
to set timetables for the reduction and/or
elimination of the production of other (e.g.,
halons) substances that can deplete stratospheric
ozone (as late as 2010 for some substances and
developing nations)
• Currently about 200 nations have agreed to one or
more provisions of the Montreal Protocol
Stratospheric Ozone
• The U.S. agreed (1992) to curtail CFC production
at the end of 1995 during the waning days of the
Bush (senior) Administration? Why?
• The CFC production ban allowed freons produced
before the ban started to be used after January 1,
1996
• The CFC ban temporarily produced another Black
Market economy! In 1996 the value of illicit CFCs
smuggled into the US was second only to the
value of illicit cocaine
Stratospheric Ozone
• What are the CFC substitutes now being
used in new air conditioners, refrigerators
and other cooling units? Two types: HFCs hydrofluorocarbons and HCFCs hydrochlorofluorocarbons
• The slight chemistry differences from CFCs
results in substances that are reactive in
Earth’s lower atmosphere
Stratospheric Ozone
• If the refrigerant gases react in the lower
atmosphere there’s a much lesser chance of
their Cl and F components ever reaching the
stratosphere
• Are the substitutes safe? Some evidence
suggests that the most commonly used CFC
substitute may react to form another type of
acid rain detrimental to wetlands and is a
potent greenhouse gas!
Stratospheric Ozone
• Updates:
• In early October 2006 the
area of the Antarctic
ozone hole was the largest
ever measured and
correlated to below
average stratospheric
temperatures
• Possible global warming
connection? (see figures)
Stratospheric Ozone
Source: Science News
Antarctic Ozone
2010: ~21
2010: 118
Source: NASA
Stratospheric Ozone
• The figure on the right is
from November 7, 2008
• The following link allows
you to determine the
stratospheric ozone level
overhead for anywhere up
to two days beforehand
• http://toms.gsfc.nasa.gov/t
eacher/ozone_overhead_v
8.html
Stratospheric
Ozone
Overall, these data
(hopefully) suggest
that stratospheric
ozone levels should
begin to show
modest increases
during the next 3050 years as the
Montreal Protocol
provisions lower
ozone-depleting
chemicals in the
upper atmosphere
Ground-level Ozone
• Don’t confuse stratospheric
ozone with ground-level ozone
• Ground-level ozone - ozone
produced in the lower
troposphere; a component of
photochemical smog
• Photochemical smog is
generated by UV light
interacting with fossil fuel
combustion gases; especially
nitrogen oxides (NOx)
Los Angeles, CA photochemical smog
Ground-level Ozone
• NOx + UV ----> N + O; subsequently this
reaction, O2 + O ---> O3 , generates
ground-level ozone
• You’ve probably smelled ground-level
ozone after a nearby lightning strike
• Who cares?
• The American Lung Association cites
ground-level ozone as a severe pollutant
Ground-level Ozone
• Studies suggest that prolonged exposure to
even seemingly minor amounts (150 parts
per billion) of ground-level ozone could
cause permanent lung tissue scarring and
loss of pulmonary function
• How does this relate to the “Ozone Action
Days” we hear about each summer in
southeast Michigan?
Ground-level Ozone
• What activities are we asked
to curtail or reduce on these
days?
• What impact does this issue
have for when and where we
conduct our outdoor aerobic
exercise?
Fairly Recent News
Astronomy
• Astronomers are the most “disadvantaged”
natural scientists since they rarely have the
opportunity to directly sample their objects
of interest
• Most of our astronomical knowledge has
been gained indirectly by studying various
regions of the electromagnetic spectrum
Electromagnetic Spectrum
• Electromagnetic spectrum - refers to a broad
band of energies created by the movement
of charged particles, mostly electrons
• Origin of name? The charged particle
movement generates an electric field and
with every electric field there is an
associated magnetic field, the name
electromagnetic summarizes the electric and
magnetic properties
Electromagnetic Spectrum
• The term spectrum refers to the broad band
of energies resulting from the electron
motion (see slide)
Electromagnetic Spectrum
• Studies illustrate that all electromagnetic energy
has a wave-like component of movement; e.g.,
think of the movement of a water wave
• All waves have terms used to describe them,
including the terms wave crest, wave trough, wave
height, wavelength and wave frequency
• See slide
Wave Characteristics
• Wave crest - highest elevation point of wave
• Wave trough - lowest elevation point of wave
• Wave height - vertical distance between the wave
crest and wave trough
• Wavelength - horizontal spacing between two
adjacent wave crests or two adjacent wave troughs
Wave Characteristics
• Wave frequency - the number of wave
crests, or troughs, that pass an observation
point per unit of time; one wave crest or
trough passing a counter every second is
defined as a frequency of 1 cycle per second
(1 cps) (see figure)
• 1 cps = 1 hertz (Hz)
• How is the term “hertz” familiar to you?
Wave Characteristics
• Important relationship: the higher a wave’s
frequency, the greater its impact or
penetration energy and the shorter its
wavelength
• Compare two wave examples drawn on
board - which has the higher frequency and
therefore the greater energy?
Electromagnetic Spectrum
• In our survey of the electromagnetic
spectrum, note the great variance in
wave frequencies and wavelengths as
we move from the higher energy end
(e.g., cosmic and X-rays) to the lower
energy end (radio waves) (see slide)
• Can you tell me why UV light is
potentially more damaging than visible
light?
Electromagnetic Spectrum
• Within the visible portion (violet, blue,
green, yellow orange, red) of the
electromagnetic spectrum, each color we
see has a specific wavelength and frequency
• See slide
Electromagnetic Spectrum
• Notice also that the Earth’s atmosphere is
opaque (can’t be effectively penetrated),
semi-transparent or transparent (essentially
uninhibited penetration) to different
energies of the electromagnetic spectrum
(see slide)
• In addition, how does a microwave oven
cook food?
Astronomy Applications
• Astronomers study portions of the
electromagnetic spectrum by using light,
radio, X-ray, and microwave telescopes
commonly in their research
• Applications?
• Much of our knowledge of the composition
of celestial objects (e.g., stars) stems from
observations of the light they emit
Astronomy Applications
• Background: you’ve all seen how white
light is separated into its spectral colors by a
rainbow or prism (see figure)
Astronomy Applications
• Astronomers use special devices called
spectrometers to study the light emitted by
celestial objects
• Each element (compounds too) has its own
light fingerprint
• Use the following slide to discuss why
Element-specific spectral line colors and spacing
Light emitted by element
Element heated or exposed to electrical
discharge until it emits light (glows)
Astronomy Applications
• Why does each element have an unique light
fingerprint? Think of the atom structure. A
nucleus surrounded by electrons that occupy
regions of space called energy level shells
• Electrons can be apparently boosted from the
ground (undisturbed) state to a higher energy level
(excited state) by the absorption of photons (see
slide)
Higher energy
level than
ground state
Astronomy Applications
• Photon - a small package of energy (e.g.,
light, electrical discharge)
• The electrons boosted to a higher energy
state are not stable since everything in the
universe attempts to reach the lowest
energy, highest equilibrium state
• At some point the electrons collapse
downward to their original ground state
energy level, emitting flashes of light
Astronomy Applications
• Since the number of electrons and the
distance between electron energy levels in
each atom type (e.g., C, O, Na, etc.) is
unique, the emitted light flashes (photons)
are also unique
• This light can be separated into its unique
spectral colors and spacings by
spectrometers
• See slides
(For hydrogen)
Astronomy Applications
• On Earth, we excite electrons in atoms of
different elements (compounds too), one at
a time, in a laboratory (see slide) and use
spectrometers to record their spectral
components (characteristic colors and
spacings)
Astronomy Applications
• Astronomers use light telescopes outfitted with
spectrometers to identify elements (and
compounds) in celestial objects that match the lab
results
• Today the light telescopes are outfitted with
spectrometers that are interfaced with computers;
the computers are used to distinguish the chemical
composition of objects from the blend of light they
emit
• Think about this process when you next gaze upon
a star!
Astronomy Applications
• Let’s go to the adjacent
room and view a
demonstration of the
characteristic light spectra
of selected elements
• Once we get there, be able
to explain to me how
“neon” lights work and the
origin of the Earth’s
aurora (e.g., Aurora
Borealis and Aurora
Australis)
Astronomy Applications
• So next class we’ll begin our overview of specific
astronomy topics; we’ll learn that space probes,
satellites and improved telescopes are rapidly
increasing our knowledge of astronomy
• I’ll whet your appetite with a short, time-lapse
movie/simulation capturing the descent of the
Huygens space probe, launched from its parent
probe Cassini, to the surface of Saturn’s moon
Titan in January 2005 (about 720 million miles
from Earth)
An Update