Q1: What is ozone and where is it in the atmosphere? Natascia Turrà

Q1: What is ozone and where is it in the atmosphere? Naturally present in our atmosphere as gas, O 3 Discovered in lab in mid 1800s Measured in atmosphere with chemical and optical methods Pungent odor  easily detectable Very reactive with chemical compounds and explosive in concentrated amounts Produced by electrical discharges Used for industrial processes, e.g. –air and water purification –bleaching of textiles and food products About 90% in stratosphere (10/ km altitude) Highest concentration in „ozone layer“ It extends over entire globe with variation in altitude and thickness 10% found in troposphere (0-10/16 km altitude)

Q1: What is ozone and where is it in the atmosphere? Low relative abundance in atmosphere: –at peak concentration, few thousand ozone molecules for every billion (10 9 ) air molecules [air ≈ 78% N 2 and 21% O 2 ] –near Earth‘s surface in troposphere: O 3 molecules/10 9 air molecules Highest surface values due to pollution by human activities Ozone layer thickness varies from region to region and with season All ozone put together and distributed on Earth‘s surface would give a 3 mm thick layer Vital role in protecting life on Earth

Q2: How is ozone formed in the atmosphere? Lea Jacot-Descombes

Q3: Why do we care about atmospheric ozone? Silja Püntener

Q4: How is total ozone distributed over globe? Melanie Bieli

Q4: How is total ozone distributed over the globe?  Total Ozone: sum of all the ozone in the atmosphere directly above the location where the measurement takes place  Dobson units  Strong temporal (daily to seasonal) and spatial (vertical, latitudinal and longitudinal) variations ( DU)  Source region: tropics (UV light), but largest values are found at high latitudes, lowest values in the tropics  large-scale air circulation in the stratosphere transports ozone toward the poles (Brewer-Dobson circulation)  Seasonal variations of this transport, different production/destruction rates and small-scale dynamics cause global distribution pattern

Seasonal Distribution  NH: maximum at high latitudes during spring  increased destruction during polar summer  minimum in early fall  SH: minimum in spring over Antarctica (ozone hole)  mixing with lower-altitude air  ozone hole disappears  Tropics: smaller seasonal variations due to smaller changes in transport and sunlight analysis.html

Q5: How is ozone measured in the atmosphere? Manuel Capitanio

Q6: What are the principal steps in strato-spheric ozone depletion caused by human activities? Iwan Bigler

Q6: What are the principal steps in strato- spheric ozone depletion caused by human activities? 1. Emission 2. Accumulation 3. Transport 4. Conversion 5. Chemical reaction 6. Removal

Q7: What emissions from human activities lead to ozone depletion? Mirjam Nufer

Q7 What emissions from human activities lead to ozone depletion?

Atmospheric lifetime Ozone Depletion Potential Question / Remarks Chlorine gases CFC decreasing CFC still in use CFC decreasing ODS substitue gases HCFCs Increasing, effect on global warming? HFC Bromine gases Halon very effective, still in use Halon decreasing

Q9: What are the chlorine and bromine reactions that destroy stratospheric ozone? Melanie Ruosch

Q9: What are the chlorine and bromine reactions that destroy stratospheric ozone? cycle polar region -visible sunlight required to complete each cycle, helps to form ClO -late winter/early spring – ozone destruction > ozone production cycle 1: Cl + O 3 → ClO + O 2 ClO + O → Cl + O 2 Net: O 3 + O → 2O 2 -tropical and middle latitudes -requires UV radiation to form atmic oxygen cycle 2: ClO + ClO → (ClO) 2 (ClO) 2 + sunlight→ ClOO + Cl ClOO → Cl + O 2 2 (Cl + O 3 → ClO + O 2 ) Net: 2O 3 → 3O 2 cycle 3: ClO + BrO → Cl + Br + O 2 or (ClO + BrO → BrCl + O 2 BrCl + sunlight→ Cl + Br) Cl + O 3 → ClO + O 2 Br + O 3 → BrO + O 2 Net: 2O 3 → 3O 2

Uncertainties/Problems: -chlorine and bromine are only one group of ozone destroying substances -other groups e.g. reactive hydrogen, reactive nitrogen gas -increase/decrease of substances in the future -might be difficult to estimate consequences of an increase of a substance

Q12: Is there depletion of the Arctic ozone layer? Raphaela Vogel

Q12 Is there depletion of the Arctic ozone layer?

Yes there is!

Q12 Is there depletion of the Arctic ozone layer? However... Less depletion than in Antarctic shorter period (January - March) higher average T less effective isolation of stratospheric air Higher total ozone values (near 450 DU) Higher variability chemical destruction through ODS meteorological conditions

Q13 - How large is the depletion of the global ozone layer? Dominik Büeler

Global total ozone changes: Q13 - How large is the depletion of the global ozone layer?

Scientific Uncertainties / Problems Increase after 1990: Not only because of decrease in ODS emissions --> How large is the response to the Mt. Pinatubo eruption? Influence of climate change? Aha-Effect Large influence of Mt. Pinatubo Understanding Problems Lifetimes: Tropical stratospheric air vs. polar stratospheric air?

Q16: Has the Montreal Protocol been successful in reducing ozone-depleting substances in the atmosphere? Stefan Rüdisühli

Q17: Does depletion of the ozone layer increase ground-level ultraviolet radiation? Sandro Blumer Fabian Binder

Q17 – Does depletion of the ozone layer increase ground-level ultraviolet radiation? 1.Scientific Answer Yes, ultraviolet radiation of Earth‘s surface increases as the total amount of overhead total ozone decreases. UV-B 280 nm nm Chapman mechanism: O 2 + hυ  O + O, λ ≤ 242 nm O + O 2 + M  O 3 + M O 3 + hυ  O 2 + O, λ ≤ 1 μm O + O 3  O 2 + O Largest increases at the Poles; South Pole: 55 – 80% increase for 1991 – 2006 compared to 1963 – 1980 Increased up to 6% in a wide range outside tropics, between 1979 – 2008 Smalles increases in the tropics

2. Scientific uncertainities and remaining problems Additional causes of UV changes: UV-B radiation reaching Earth‘s surface dependet on a number of factors in addition to total ozone: Position of sun (daily and seasonal cycles) Local cloudiness Altitude of location Amount of ice or snow cover Aerosols above location Estimating the impact of changes of these factors is complex Long term changes of clouds and aerosols vary on geographical width UV monitoring systems at several surface locations since Question Why is the increase in the UV radiation in the tropics so small? (  Circulation or PSC).

Q19: Have reductions of ozone-depleting substances under the Montreal Protocol also protected Earth’s climate? Ivo Suter

Have reductions of ozone-depleting substances under the Montreal Protocol also protected Earth ’ s climate? GWP emission offset (~30% of effect): 1)ODS reduce the greenhouse gas ozone 2)Substances replacings ODS are greenhouse gases too Emission reduction of ODS in 2010 is about 9.7–12.5 GT CO2-equivalent / y. Kyoto Protocol target is 2 GT CO2- equivalent / y. (Without ODS)

Same offset as GWP The already emmitted ODS will continue to contribute to Radiative forcing. Lifetime of decades to centuries Have reductions of ozone-depleting substances under the Montreal Protocol also protected Earth’s climate? Yes!

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