Presentation on theme: "Q1. What is ozone and where is it in the atmosphere? Simone Brunamonti."— Presentation transcript:
Q1. What is ozone and where is it in the atmosphere? Simone Brunamonti
Ozone is a gas molecule denoted O 3, 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. WHAT IS OZONE?
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. WHERE IS OZONE IN THE ATMOSPHERE?
Q2. How is ozone formed in the atmosphere? Lukas Bühler
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. September11Thomas 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. September12Thomas 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 motions 2.Changes in the balance of chemical production and loss processes
Q5. How is ozone measured in the atmosphere? Dominik Bitschnau
RemoteIn 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 Limitatio n -Total O 3 along path-Point measurement [NOAA, 2010] dcb/2012/09/26 How is ozone measured in the atmosphere?
Chemoluminiscence Excited intermediate Equal to NO x determination Emission proportional to [O3] UV absorbtion max. absorbtion at 250nm Standard method Lambert-Beer Law [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.Emissions of halogen source gases at Earth‘s surface 2. Accumulation in the atmosphere (highly unreactive in the lower atmosphere) 3.Transport to the stratosphere by air motions 4. Conversion in the stratosphere to reactive halogen gases (chemical reactions involving UV- radiation) 5. Chemical reaction chemical depletion of stratospheric ozone PSCs: singnificantly increase of reactive halogen gases in polar regions in winter/spring 6.Removal by 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 Question 7 What emissions from human activities lead to ozone depletion? 20Question 7 - Martha Vogel27.09.2012
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-depleting substances 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) ① T < -78°C: PSCs form –ClONO 2 + HCl -> Cl2 + HNO3 –Cl is an ozone depleting catalyst –Even more effective when denitrification occurs ② Polar vortex isolates the polar airmass –Increases as T decrease in winter (high T gradients) –ODS cannot escape ③ Catalytic cycles become active with sunlight
... and what about the Arctic? No long-lasting ozone-holes as such! ① Temperatures are on average higher and more variable, so PSCs don‘t tend to exist for long ② Polar vortex is not that strong
Q14 Do 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 ↑→ O 3 ↑ O 2 + hν → 2 O O + O 2 + M → O 3 + M Volcanic eruption: Volcanic particles (sulfate particles) ↑ → solar transmission ↓ → O 3 ↓ 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 → O 3 variation: 1 – 2% Volcanic eruption: Mt. Agung (1963, EESC low) → O 3 unaffected El Chichón (1982, EESC high) Mt. Pinatubo (1991, EESC very high) → O 3 temporarily ↓ until volcanic particles (short residence time) are removed by natural processes Changes in the sun and volcanic eruptions affect the ozone layer but they cannot account for the continuous long-term decrease of global ozone over 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.
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 21 st 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
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