Q1. What is ozone and where is it in the atmosphere?

Simone Brunamonti

Ozone is a gas molecule denoted O3, discovered in

laboratory experiments in the mid-1800s, composed

of three oxygen atoms bound together.

Very reactive molecule, explosive in concentrated

amounts, used for several industrial processes.

Naturally present in our atmosphere, even if in a very low concentration.

Plays a fundamental role in protecting life on Earth, as it protect us from the harmful solar uv-radiation.

Atmospheric ozone is diffused all over the globe, but its vertical distribution is not uniform through the atmosphere.

About 90% of atmospheric ozone is

located inside the stratosphere, in

the OZONE LAYER (15 - 35km height).

Recently discovered (1970’s) that some

human produced chemicals could lead to the

depletion of the ozone layer.

Remaining 10% of ozone is found in the

troposphere, the lower region of atmosphere.

Here we can find local (dangerous)

increases of ozone concentration as a result

of pollution from human activities.

Q2. How is ozone formed in the atmosphere?

Lukas Bühler

Q2: How is ozone formed in the atmosphere?

Q2: How is ozone formed in the atmosphere?

Q3. Why do we care about atmospheric ozone?

Larissa Lacher

Q4. How is total ozone distributed over the globe?

Thomas Leutert

How is the total ozone distributed over the globe?

• Spatial Variation:– Most ozone in the stratosphere (about 90%)– Largest total ozone values in middle and high latitudes– Values of total ozone lowest in the tropics

IACETH

Donnerstag, 27. September 11 Thomas Leutert

• Determing factors:– Ozone production (solar ultraviolet radiation)– Large scale air circulation in the stratosphere to the poles– Removal/chemical destruction of the ozone

IACETH

Donnerstag, 27. September 12 Thomas Leutert

• Seasonal Variation:– Antarctic: Ozone hole in spring– Arctic: Increasing values during

winter, maximum in spring, decreasing values from summer to fall

– Low latitudes: Small changes

• Natural Variations:– Changes with latitude and

longitude on daily to weekly timescales

– Reasons:1. Natural air motions2. Changes in the balance

of chemical production and loss processes

Q5. How is ozone measured in the atmosphere?

Dominik Bitschnau

Remote In Situ

How - Active: laser- Passive: starlight,

sunlight- Radiation detector

- Reaction chamber

What - UV absorbtion - Electrical curent- Absorbtion (UV)- Emission

Platform - Satellites- Ground- Aircraft

- Ballloon sonde- Aircraft

Limitation

- Total O3 along path - Point measurement

[NOAA, 2010]

dcb/2012/09/26

How is ozone measured in the atmosphere?

How is ozone measured in the atmosphere?

Chemoluminiscence

• Excited intermediate

• Equal to NOx determination

• Emission proportional to [O3]

UV absorbtion

• max. absorbtion at 250nm

• Standard method

• Lambert-Beer Law

[Tethys, 2006]

[Tethys, 2006]

dcb/2012/09/26

Q6. What are the principal steps in stratospheric ozone depletion

caused by human activities?

Annika Langenbach

Q6: What are the principal steps in stratospheric ozone depletion caused by human activities?

1. Emissionsof halogen source gases at Earth‘s surface

2. Accumulationin the atmosphere (highly unreactive in the lower atmosphere)

3. Transportto the stratosphere by air motions

4. Conversionin the stratosphere to reactive halogen gases (chemical reactions involving UV-radiation)

5. Chemical reactionchemical depletion of stratospheric ozone

PSCs: singnificantly increase of reactive halogen gases in polar regions in winter/spring

6. Removalby moisture in clouds and rain in the trosposphere, after return to trophosphere

Q6: What are the principal steps in stratospheric ozone depletion caused by human activities?

• Some halogen gases are emitted from natural sources – part of the natural balance

• Some halogen source gases undergo chemical conversion in the troposphere– Gases with longer lifetimes have slower conversion

rates

• Understanding of stratospheric ozone depletion:– Laboratory studies– Observations– Computer models

Q7. What emissions from human activities lead to ozone depletion?

Martha Vogel

emissions of ozone-depleting substances (ODSs)

ODSs: halogen source gases of human activities controlled by the Montreal Protocol

20Question 7 - Martha Vogel 27.09.2012

21Question 7 - Martha Vogel 27.09.2012

Q9. What are the chlorine and bromine reactions that destroy

stratospheric ozone?

Denis Jorisch

Stratospheric Ozone Destruction at tropical and middle latitudes

- Involves two separate chemical reactions.

- Atomic oxygen (O) is formed when solar ultraviolet radiation (sunlight) reacts with ozone and oxygen molecule.

- Low abundance of atomic oxygen limits ozone loss in cycle 1

- Cycle 1 is most important in the stratosphere at tropical and middle latitudes, where solar ultraviolet radiation is most intense.

Stratospheric Ozone Distruction in Polar Regions

- During winter as a result of reactions on the surface of PSC.- Cycles 2 and 3 account for most of the ozone loss observed in the Arctic and Antarctic

stratospheres in the late winter/early spring season.- During polar night and other periods of darkness, ozone cannot be destroyed by these

reactions.

Q10. Why has an “ozone hole” appeared over Antarctica when ozone-depletingsubstances are present throughout the

stratosphere?

Silvia Reynolds

Why has an ozone hole appeared over Antarctica when ozone-depleting substances

are present throughout the Stratosphere?

Requirements: low T (1) + isolation (2) + sunlight (3)

①T < -78°C: PSCs form

– ClONO2 + HCl -> Cl2 + HNO3

– Cl is an ozone depleting catalyst– Even more effective when denitrification occurs

②Polar vortex isolates the polar airmass– Increases as T decrease in winter (high T gradients)– ODS cannot escape

③Catalytic cycles become active with sunlight

... and what about the Arctic?

No long-lasting ozone-holes as such!

①Temperatures are on average higher and more variable, so PSCs don‘t tend to exist for long

②Polar vortex is not that strong

Q14Do changes in the Sun and volcanic eruptions affect the ozone layer?

Claudia Mignani

Q14 Do changes in the Sun and volcanic eruptions affect the ozone layer?

Changes in the Sun:

• Solar radiation ↑ → O3 ↑

O2 + hν → 2 O

O + O2 + M → O3 + M

Volcanic eruption:

• Volcanic particles (sulfate particles) ↑

→ solar transmission ↓

→ O3 ↓

But: ozone response depends on the amount of equivalent effective

stratospheric chlorine (EESC):

Low EESC → ozone decreases slightly

High EESC → ozone decreases significantly

Q14 Do changes in the Sun and volcanic eruptions affect the ozone layer?

Changes in the Sun:• 11-year solar cycle

→ O3 variation: 1 – 2%

Volcanic eruption:

• Mt. Agung (1963, EESC low)

→ O3 unaffected• El Chichón (1982, EESC high)

Mt. Pinatubo (1991, EESC very high)

→ O3 temporarily ↓ until volcanic particles (short residence time) are removed by natural processes

Changes in the sun and volcanic eruptions affectthe ozone layer but they cannot account for thecontinuous long-term decrease of global ozoneover the last three decades

Q15. Are there controls on the production of ozone-depleting

substances?

Kevin Winter

Q15: Are there controls on the production of ozone-depleting

substances?

• Yes, 1987: Montreal Protocol on substances that deplete the ozone layer

• Legally binding controls of halogen source gases (chlorine & bromine) ODSs

• Further amendments: London (1990), Copenhagen (1992), Vienna (1995), Bejing (1999), Montreal (2007), all nations signed (2010)

• Zero-emissions in 2011, but not yet completed

• Difficulties (and aha-effect):– HCFCs (hydrochlorofluorocarbons): short-term

substitutes– More reactive in troposphere

88-98% less effective than CFC-12– Phase-out of HCFCs in 2030

– HFCs (hydrofluorocarbons): long-term substitutes– Do not contribute the ozone depletion– But are strong greenhouse gases (because of long

lifetime)

• Remaining Question:– Why do HFCs not contribute to ozone depletion (while

HCFCs do)?

Question 16:Has the Montreal Protocol

been successful in reducing ozone-depleting substances in

the atmosphere?

Deniz Ural

• YES!• ODS* decrease after Montreal Protocol (MP).• ODS reduction depends on

– how rapidly an ODS is used and released to the atmosphere after being produced

– the lifetime (τ) for the removal of the ODS from the atmosphere. Short τ faster removal and no storage

• EESC**: – Measure of success of MP. – Measure of potential Ozone depletion in the stratosphere that can

be calculated from atmospheric surface abundance of ODS and natural chlorine and bromine containing gasses.

– How to calculate: measurements, past values, projections– Long term trend: 1950-1990: steady increase, after MP: slow down

of increase and started to decrease. Back to 1980 values will take several decades.

* ODS: Ozone depleting substance** EESC: Effective Equivalent Stratospheric Chlorine

• CFC: τ = 45-100 years. Ended in 1996 (developed countries) and 2010 (developing countries).

• Halons: Bromine containing ODS. τ = 65 years. Ended in 1994 and 2010.

• Methyl Chloroform: τ = 5 years. No storage. Ended in 1996 and 2015.

• HCFC substitute gases: Lesser threat to Ozone. Increasing trend. Phase out in 2020 and 2030.

• Carbon tetrachloride: Phased out in 1996 and 2010. Less rapid decrease then expected. either larger than reported emissions or τ is longer than estimated.

• Methyl chloride methyl bromide: distinct among halogen source gases because substantial fractions of their emissions are associated with natural processes.

Q19. Have reductions of ozone-depleting substances under the Montreal Protocol also protected

Earth’s climate?

Martin Stolpe

Have reductions of ozone-depleting substances under the Montreal Protocol also protected Earth’s

climate?

Martin Stolpe

Yes, ozone-depleting substances (ODSs) are also greenhouse gases

Q20: How is ozone expected to change in the coming decades?

Blaž Gasparini

Recovery of ozone layer from the effects of ozone-depleting substances (ODS) near the middle of the 21st century.

•In future: minor role of ODS and bigger influence of climate

•Model projections: strengthening of Brewer-Dobson circulation -> bringing more ozone to the polar regions -> less in tropics

Ozone recovers before ESC – stratospheric cooling and strengthened circulation effect

Why we can we trust the main finding with a certain degree of confidence?

ESC = Equivalent Strat. Clorine

•Uncertainties mostly connected to climate change induced circulation differences•My “aha!”: Why tropics less sensitive to changes in ODS than polar regions?

Polar air: ESC values bigger => transport (up to several years) => more time for conversion of ODS to reactive halogen gasses