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Stratospheric Ozone. Science Concepts Ozone Chemistry Creation Process Destruction Processes Equilibrium CFC Chemistry Polar Vortex. Stratospheric Ozone Ozone Chlorofluorocarbons (CFCs) CFCs Antarctic Ozone Hole Causes Ozone and Surface uv Radiation Effects of uv on Life

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Stratospheric ozone

Stratospheric Ozone

Science Concepts

Ozone Chemistry

Creation Process

Destruction Processes

Equilibrium

CFC Chemistry

Polar Vortex

Stratospheric Ozone

Ozone

Chlorofluorocarbons (CFCs)

CFCs

Antarctic Ozone Hole

Causes

Ozone and Surface uv Radiation

Effects of uv on Life

Mitigation

The Earth System (Kump, Kastin & Crane)

•Chap. 1 (pp. 7-9)•Chap. 11 (pp. 219-220)•Chap. 17 (pp. 343-359)


Ozone

Ozone

Ozone in the Earth’s Atmosphere

Stratosphere

Stratospheric ozone is “good.” It protects Earth’s surface from Sun’s harmful ultraviolet radiation.

90% of ozone is in the stratosphere.

Troposphere

Tropospheric ozone is “bad.” It can damage lung tissue and plants.

Mesosphere


Ozone1

Ozone

Ozone

•Three atoms per molecule

instead of the normal oxygen

molecule with two atoms

•Maximum near 25 km

•90% of ozone in stratosphere

•Secondary max near ground

Fahey, D.W., Twenty Questions and

Answers About the Ozone Layer.

http://vortex.nsstc.uah.edu/atmchem/recent_events/

upperstrat03_recovery.html


Stratospheric ozone chemistry

Vis-

ible

Near

IR

UV

Far Infrared

H

O

2

CO

2

100

O

O

,

3

CO

,

2

2

CO

,

2

Absorption (%)

O

H

O

3

2

H

O

2

H

O

2

50

0

0.3

0.5

1.0

5.0

10.0

15.0

20.0

Wavelength (microns)

Stratospheric Ozone Chemistry

Stratospheric Ozone Production

•Stratospheric ozone production

O2 + uv => O + O

O2 + O => O3

Fahey, D.W., Twenty Questions and

Answers About the Ozone Layer.

http://vortex.nsstc.uah.edu/atmchem/

recent_events/upperstrat03_recovery.html


Stratospheric ozone chemistry1

Stratospheric Ozone Chemistry

Four Major Natural Ozone Destruction Processes

•Chapman process; uv (0.2 - 0.3 microns) radiation

O3 + uv => O2 + O

•Collisions with atomic oxygen

O3 + O => 2 O2

•Collisions with itself

O3 + O3 => 3 O2

•Collisions with nitric oxide; for

example

NO + O3 => NO2 + O2

NO2 + O => NO + O2

Note nitric oxide molecule ends up being able to participate in another

reaction; thus, nitric oxide is said to be catalytic

Fifth Natural Destruction Process (Intermittent)

Volcanoes add sulfuric gases into the stratosphere that produce particulates that interact to increase ozone destruction


Stratospheric ozone chemistry2

Stratospheric Ozone Chemistry

Equilibrium

•Bucket with water pouring into it and

four holes near the bottom of it

-What if we continue the inflow?

-What will happen to the water level?

-As the depth of water increases,

the pressure at bottom increases

thereby increasing the rate of

outflow until the rate of outflow

balances the rate of inflow

•State of balance between opposing

forces or actions that is either static or

dynamic*

•A state of adjustment between opposing

or divergent influences or elements*

* Webster’s New Collegiate Dictionary


Stratospheric ozone chemistry3

Stratospheric Ozone Chemistry

Equilibrium (Con’t)

•What if we reduce the inflow rate?

-Equilibrium level will be lower


Stratospheric ozone chemistry4

Stratospheric Ozone Chemistry

Equilibrium (Con’t)

•What if we increase the inflow rate?

-Equilibrium level will be higher


Stratospheric ozone chemistry5

Stratospheric Ozone Chemistry

Equilibrium (Con’t)

•What if we decrease the number

or size of the outflow holes?

-Equilibrium level will be higher

•What if we increase the number

or size of the outflow holes?

-Equilibrium level will be lower


Stratospheric ozone chemistry6

Stratospheric Ozone Chemistry

Equilibrium (Con’t)

•Equilibrium level changes as the

-Rate of inflow changes

-Number and/or size of the outflow holes change

Principle

•Depth (distance between top of water and level of

the holes) of water (pressure at the hole)

determines force and rate of water exiting tank,

i.e., gravity acting on the water forces water

through lower-level outflow holes

Depth

Depth


Stratospheric ozone chemistry7

Stratospheric Ozone Chemistry

Ozone Equilibrium

•Ozone rate of creation (inflow) is balanced by

rate of destruction (outflow)

-Creation depends on amount of oxygen and

uv while rate of destruction depends on

amount of ozone (depth of water) and the

destruction processes

Creation

Ozone

Amount

Destruction


Stratospheric ozone chemistry8

Stratospheric Ozone Chemistry

Ozone Destruction Variability

•Solar sunspot activity with 11-year cycle increases cosmic rays (high-

energy atomic nuclei and atomic particles) which separate the nitrogen

molecule into atomic nitrogen which then combines with oxygen to make NO.

Observed 12% variation in ozone amount because of solar cycle.

•Increased nitrogen oxides because of increased anthropogenic release

(combustion products and fertilizers)

•Additional destruction process

-Release of manmade chlorofluorocarbons (CFCs)


Chlorofluorocarbons

Chlorofluorocarbons

Background •Invented in the late 1930s •Variety of molecules consisting of atoms of hydrogen (H), carbon (C), fluorine (F) and chlorine (Cl) •For example, CCl3 (CFC-11), CCl2F2 (CFC-12), CHClF2 (CFC-22), etc. •Freon, Dupont trade name, used in refrigeration, air conditioners, cleaning solvents for electronic components, foaming agents for plastics, and aerosol propellants•Manufactured to be chemically inert and volatile•Currently releasing about 1 million tons of CFCs per year to the atmosphere•During the 70s, 80s and early 90s CFCs in the atmosphere were increasing by 5-7% per year


Chlorofluorocarbons1

Chlorofluorocarbons

Background (Con’t) •CFCs in the lower atmosphere are not removed by photodissociation,

rainout or oxidation; require ultraviolet (uv; 0.23 microns) light to be

destroyed

•Solar radiation with wavelength less than 0.29 microns is absorbed by the

ozone layer

•Thus, CFCs are not destroyed until they are diffused to altitudes 25 to

40 km


Stratospheric ozone chemistry9

Stratospheric Ozone Chemistry

Ozone Destruction by CFCs

•Chlorine and ozone react in two step

chain reaction

Cl + O3 => ClO + O2

ClO + O => Cl + O2

•Note chlorine atom ends up being

able to participate in another reaction;

thus, chlorine is said to be catalytic

•Chlorine is finally removed when it

combines with hydrogen (H) to make

hydrochloric acid (HCl)

Cl + H => HCl

http://veimages.gsfc.nasa.gov/56/

ozone_destruction_final.mov


Stratospheric ozone chemistry10

Stratospheric Ozone Chemistry

Summary

•Follow image steps 1

through 5

http://www.cmdl.noaa.gov/infodata/faq_cat-2.html#31


Stratospheric ozone chemistry11

Stratospheric Ozone Chemistry

Ozone Destruction by CFCs (Con’t)

•Chlorine atoms last 1 to 2 years before combining with hydrogen; during this

time they participate in as many as 100,000 reactions with ozone

•All in all the chlorine in some CFCs stay in the atmosphere about 100 years

from the time they are first released until they are finally rained out

Natural Chlorine

•Naturally, oceans add chlorine gases to the atmosphere; most of this chlorine

does not reach the stratosphere


Stratospheric ozone chemistry12

Stratospheric Ozone Chemistry

Ozone Dobson Units (DU)

•Note ozone is most frequently

measured in Dobson Units

O3

If all the Ozone over a certain area were compressed at O°C and 1 atm pressure, it would form a slab about 3 mm thick.

This would correspond to 300 DU.


Antarctic ozone hole

Antarctic Ozone Hole

Description

•Antarctic

ozone in the

70s versus the

80s and 90s

http://toms.gsfc.nasa.gov/multi/buv-toms.gif


Antarctic ozone hole1

Antarctic Ozone Hole

Description (Con’t)

•Comparison of

Antarctic ozone in

the 70s versus

90s

•60% reduction in

early October

over Antarctica

http://see.gsfc.nasa.gov/edu/SEES/strat/class/Chap_11/11_Js/11-03.jpg


Antarctic ozone hole2

Antarctic Ozone Hole

Minimum

Folklore has it

•1985 measurements

of the stratospheric

ozone levels drop

were so dramatic,

scientists thought

their instruments

were faulty.

•TOMS satellite data

didn't show the

dramatic loss of ozone

because software

processing the raw

ozone data from the

satellite was

programmed

to treat very low

values of ozone as bad readings!

http://toms.gsfc.nasa.gov/eptoms/dataqual/oz_hole_annual_min_v8.jpg


Antarctic ozone hole3

Antarctic Ozone Hole

September 24, 2006

Development (Con’t)

•Global average ozone layer thickness is about

300 Dobson Units

•Ozone

hole is

region over

Antarctica with

total ozone 220

Dobson Units or lower

•Occurs in southern hemispheric

spring (October) after southern

hemispheric winter that has no

sunlight and is very cold

•2005 ozone hole development -

July through December

http://earthobservatory.nasa.gov/Newsroom/

NewImages/images.php3?img_id=17436

http://earthobservatory.nasa.gov/Newsroom/

NewImages/images.php3?img_id=17116


Antarctic ozone hole4

Antarctic Ozone Hole

http://earthobservatory.nasa.gov/Newsroom/

NewImages/images.php3?img_id=17809

September 13, 2007

Depth and Size

•22 million square km is slightly less

than North American continent

•9/21-30/06, average area of ozone hole

largest ever, at 10.6 million square miles

http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003136


Antarctic ozone hole5

Antarctic Ozone Hole

Explanation

•In winter and early

spring, little to no

solar radiation. Thus,

no uv to create ozone.

•Polar vortex (clockwise at high

altitudes) wind pattern develops;

cuts off air exchange with southern

hemisphere midlatitude air. Thus,

ozone is not imported.

•Recall stratosphere is heated

primarily by absorption of solar

ultraviolet (uv) radiation by ozone,

while stratosphere is primarily cooled

by emission of infrared (IR) radiation

to space by carbon dioxide, ozone,

and water vapor

During polar winter, solar heating by

ozone ends and the Antarctic

stratospheric air

becomes very cold

http://see.gsfc.nasa.gov/edu/SEES/strat/class/Chap_11/index.htm


Antarctic ozone hole6

Antarctic Ozone Hole

Explanation (Con’t)

•With temperatures below -80°C

(-112°F) during winter, high, thin

clouds of water, sulfuric acid,

nitric acid (polar stratospheric

clouds, PSCs) form at high

altitudes (~70 kft; in the

stratosphere).

-Normally, clouds don’t

form in the stratosphere

because it is too dry

-At high latitudes during

winter, stratospheric

temperature can become

so cold that clouds of other

several gases can form

Fahey, D.W., Twenty Questions and Answers About the Ozone Layer

http://vortex.nsstc.uah.edu/atmchem/recent_events/upperstrat03_recovery.html


Antarctic ozone hole7

Antarctic Ozone Hole

Explanation (Con’t)

•Cloud droplets provide a surface upon

which chlorine species like CFCs can

breakdown to yield chlorine molecules

(Cl2). These reactions occur during the

polar night. By mid winter, most chlorine

inside the southern lower stratospheric

vortex is in the form of Cl2.

•Cl2 reacts to sunlight to form atomic

chlorine. Thus, clouds enhance creation

of atomic chlorine if sunlight is present.

http://see.gsfc.nasa.gov/edu/SEES/strat/class/Chap_11/index.htm


Antarctic ozone hole8

Antarctic Ozone Hole

Explanation (Con’t)

•Spring arrives and provides

sunlight

•Now have an abundance

of chlorine to destroy

ozone

•Ozone concentration

take a rapid, deep

plunge until the

vortex breaks up in

late spring and

re-supply of ozone

from midlatitudes can

occur

http://see.gsfc.nasa.gov/edu/SEES/strat/class/Chap_11/index.htm


Arctic ozone

Arctic Ozone

•Northern Hemisphere ozone is now showing some depletion signs

•1997 spring ozone minimum -

March through May

Fahey, D.W., Twenty Questions and Answers About the Ozone Layer.

http://vortex.nsstc.uah.edu/atmchem/

recent_events/upperstrat03_recovery.html


Global ozone depletion

Global Ozone Depletion

•Antarctic depletion up to 50%

•3% depletion in Northern Hemisphere


Global ozone depletion1

Global Ozone Depletion

Global Total Ozone

Change

•Comparison of global

average ozone in the

‘64 - ’80 versus ‘80s

and ‘90s

•3 - 4% reduction

•Dramatic dip in 1992

and 1993 caused by

eruption of Mt. Pinatubo

in Philippines

Fahey, D.W., Twenty Questions and

Answers About the Ozone Layer.

http://vortex.nsstc.uah.edu/atmchem/

recent_events/upperstrat03_recovery.html


Global ozone depletion2

Global Ozone Depletion

Global Total Ozone

Change (Con’t)

•Latitudinal distribution of

ozone change

Global Sunburning uv

Change

•Change from 1979 to 1992

Fahey, D.W., Twenty Questions and

Answers About the Ozone Layer.

http://vortex.nsstc.uah.edu/atmchem/

recent_events/upperstrat03_recovery.html


Why the big deal

Vis-

ible

Near

IR

UV

Far Infrared

H

O

2

CO

2

100

O

O

,

3

CO

,

2

2

CO

,

2

O

H

O

Absorption (%)

3

2

H

O

2

H

O

2

50

0

0.3

0.5

1.0

5.0

10.0

15.0

20.0

Wavelength (microns)

Why the big deal?

•Ozone absorbs ultraviolet light; uv-B especially

•Ultraviolet light is very harmful to living

organisms including humans

-Destroys acids on DNA molecule that

transmit heredity blueprint

-Long term exposure can cause skin cancer

-Can cause cataracts

-Suppressed immune system

uv-A

Ozone Layer

uv-B

Fahey, D.W., Twenty Questions and

Answers About the Ozone Layer.

http://vortex.nsstc.uah.edu/atmchem/

recent_events/upperstrat03_recovery.html


Why the big deal1

Why the big deal?

Global Total Ozone Distribution

•Ozone concentration

varies with latitude and

longitude

-More in polar

and mid-latitude

regions especially

northern hemisphere

-Less in tropics

Annual Average Atmospheric Ozone

http://isccp.giss.nasa.gov/products/browsed2.html


Why the big deal2

Why the big deal?

Average Atmospheric Ozone

Global Total Ozone Distribution

•Ozone concentration varies with season

-Lower values in polar regions

in winter and spring

DJF

JJA

http://isccp.giss.nasa.gov/products/browsed2.html


Why the big deal3

Why the big deal?

•Change in uv radiation with change in ozone

-Note 10% depletion

observed to cause

about 15% increase

in surface uv

-Note as ozone

depletion increases

surface uv increases

more rapidly, i.e.,

this is a non-linear

response

World Meteorological Organization

http://www.wmo.ch/index-en.html


Why the big deal4

Why the big deal?

Erythemal uv

•Erythemal uv,

sunburn

causing uv

•Lauder, New

Zealand

(45.0°S,

169.7°E)

•Note annual

cycle - maximum

in January;

Minimum in

June

•Increasing January maximum;

Red line = eyeball fit to peak values

http://environment.govt.nz/indicators/ozone/uv.html


Why the big deal5

Why the big deal?

Erythemal uv (Con’t)

•EPA estimates 1% increase in uv will cause 2% to 5% increase in skin

cancer. According to the NYU School of Medicine risk of developing

malignant melanoma was 1 in 250 in 1980 and is 1 in 87 in 1997.

•200 plant species tested, 2/3 react to increased uv

•Reduced leaf size, stunted growth, poor seed quality, increased susceptibility

to weeds, disease and pests

•Can kill phytoplankton

•More research needs to be done


What to do

What to do?

Corrective Measures

•Ban CFCs, but not easy to do

•1978 U.S. banned CFCs in aerosol sprays

•Dupont is developing new non-chlorine based chemical for automobile air

conditioners

•1988 Dupont announced phase out of production by year 2000

•1988 43 nations signed the Montreal Protocol agreeing to gradually reduce

CFC to 50% of the 1986 amounts by 2000. By 1988 many CFC-consuming

countries had ratified this agreement.


Montreal protocol

Montreal Protocol

Effects of Corrective Measures

•Predictions of stratospheric chlorine and skin

cancer from various international agreements

to reduce CFCs

Fahey, D.W., Twenty Questions and

Answers About the Ozone Layer.

http://vortex.nsstc.uah.edu/atmchem/

recent_events/upperstrat03_recovery.html


Montreal protocol1

Montreal Protocol

Effects of Corrective

Measures (Con’t)

•Surface measurements

of CFCs in the

atmosphere show the

Protocol is working

•Concentrations of

other destructive

chemicals are still

increasing. Must stop

increase in production

of methylchloride

and carbon

tetrachloride cleaning

agents


Montreal protocol2

Montreal Protocol

Effects of Corrective

Measures (Con’t)

•Model predicted recovery of

stratospheric ozone

•Note it is around 2050 before ozone

recovers to 1980 values

Fahey, D.W., Twenty Questions and

Answers About the Ozone Layer.

http://vortex.nsstc.uah.edu/atmchem/

recent_events/upperstrat03_recovery.html


Ams ozone statement

AMS Ozone Statement

Adopted by the American Meteorological Society Council on 5 September 2003)

Ozone is an important trace gas in our atmosphere that has both beneficial and damaging aspects. Naturally occurring in both the troposphere and stratosphere, stratospheric ozone has a beneficial effect for life on earth as a filtering agent for damaging ultraviolet radiation. When photochemically produced in the troposphere to sufficiently high levels, however, ozone can be toxic and can result in significant physiological and ecological damage.

Bulletin American Meteorological Society, 2004, 85, 297-299


Ams ozone statement1

AMS Ozone Statement

Human activities are causing changes in ozone levels in much of the atmosphere. By the use of stratospheric ozone depleting chemicals, humankind has caused a decrease in stratospheric ozone. Combustion of fossil fuels in motor vehicles and in stationary power plants has led to increases in nitrogen oxides and volatile organics emissions into our troposphere. Interacting together in sunlight, nitrogen oxides and hydrocarbons are causing increases in tropospheric ozone. This is especially noticeable during pollution episodes in urban centers as photochemical smog events. Tropospheric ozone increases on regional and global scales can lead to agricultural loss and ecological damage. Increases at the global scale can also contribute to global warming. While many facets of ozone's atmospheric behavior are well understood, a large number of important uncertainties remain, whose resolution will require substantial combined efforts by the meteorological and chemical communities. The American Meteorological Society (AMS) strongly supports interactions between these communities focused on obtaining a better understanding of ozone and its behavior.


Ams ozone statement2

AMS Ozone Statement

The AMS recognizes that human activities are affecting atmospheric ozone by depleting stratospheric ozone and by increasing ground-level ozone worldwide, especially in polluted urban centers. Stratospheric ozone depletion leads to increased amounts of damaging ultraviolet radiation reaching the earth's surface. This is detrimental to the atmosphere, ecosystems, and humankind, and has led to the Montreal Protocol banning stratospheric ozone-depleting chemicals. Increased ground-level ozone concentrations have direct health effects on plants, animals, and humans. Concerns here have led to the Clean Air Act Legislation aimed at the reduction of tropospheric ozone precursor emissions. Tropospheric ozone and its precursors can also have an impact on greenhouse warming.


Ams ozone statement3

AMS Ozone Statement

2) The AMS notes that the chemical, radiative, and dynamical components of ozone's behavior are coupled and complex. This complexity adds substantial uncertainty to many of the currently available assessments of ozone's impacts. Despite these uncertainties, however, ample evidence substantiates that atmospheric ozone has been affected in important and even critical ways by human activity. Stratospheric depletion has been established by observations of the Antarctic ozone hole, and our evidence that it results from human-produced halocarbons is overwhelming. Anthropogenic activities also significantly influence tropospheric ozone. Photochemical smog is well documented in most urban centers of the world, and in many cities leads to ozone levels approximately ten times higher than occurs naturally. Air pollution from the combustion of fossil fuels has caused increases in ground-level ozone throughout the Northern Hemisphere, where average ozone levels have increased by 50% or higher. Although it is uncertain how specific emissions of pollutants affect tropospheric ozone, it is certain that the increases in tropospheric ozone are associated with emissions of nitrogen oxides (NOx) and volatile organic compounds (VOCs).

The effects in both the stratosphere and troposphere are sufficiently profound to mandate substantial concern, both on a local and global basis.


Ams ozone statement4

AMS Ozone Statement

3) While human activity clearly causes changes in the atmospheric concentration of ozone, there remain important gaps in our understanding of ozone's complex behavior. This is particularly the case for tropospheric ozone, where the NOx and VOC interactions are still being unraveled and the importance of long-range transport and mixing is being resolved. In order to satisfactorily forecast future ozone trends in our atmosphere and provide a firm basis for policy analysis and associated policy actions, the lack of understanding needs to be addressed.

4) Many uncertainties arise because of the strong couplings among chemistry, radiation, and atmospheric dynamics. Thus, resolution of the uncertainty will require coordinated effort among scientists having chemical and meteorological backgrounds. The AMS actively supports continuing forums for this scientific interaction and welcomes interactions with other scientific organizations for this purpose.

Current ozone-control legislation and international agreements (such as the Montreal Protocol) tend to reflect the uncertainties noted above. Nonetheless, the actions associated with the Montreal Protocol and its associated amendments have been based on the best science available.


Ams ozone statement5

AMS Ozone Statement

Implementation of the U.S. Clean Air Act is burdened by uncertainties about the relative impact of emissions of NOx and VOCs on tropospheric ozone during pollution events, and by the failure to use observation-based investigations of ozone and ozone precursors to evaluate the impact of control strategies. Directed research should address these issues. Research also needs to identify the increasing impact of international and intercontinental transport of tropospheric ozone and its precursors, as further industrialization leads to increases in ground-level ozone worldwide.

With regard to the Montreal Protocol, it is encouraging to note that halocarbon limitations under this agreement appear to have resulted, recently, in decreases of some of the shorter-lived halogen-containing species and an end to increases of chlorofluorocarbons. Increasing reliance on replacement compounds should lead to the recovery of the stratospheric ozone system in the latter part of the twenty-first century. Owing to the noted uncertainties and complexities associated with stratospheric ozone depletion, however, the effects of this and other international agreements must be monitored continuously and carefully to confirm the expected recovery and establish the basic understanding required for more effective maintenance in future years.


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