Ozone & Ozone Depletion

1. Ozone & Ozone Depletion

2. Ozone Structure The structure of ozone makes it unstable. It breaks down into oxygen gas in a matter of several days under normal temperatures. • It has a bluish color, exists in gaseous form, has an acrid odor, and is toxic. • In the troposphere it is easily created from lightning strikes, mechanical motors, photocopying machines, and from primary air pollutants in the formation of photochemical smog. • In the troposphere it is commonly used as a disinfectant in water and waste water treatment due to its toxicity to pathogens. • In the stratosphere it absorbs UV radiation (only UV-C and part of UV-B) from entering the earth’s troposphere – thus reducing the mutational effects (skin cancers) from the UV.

4. NaturalCycle of Ozone Formation & Breakdown in the Stratosphere UV Formation: O2 O + Othen O + O2  O3 ‘O’ by itself is called an ‘oxygen radical’ – which only lasts for a very short time before combining with something else. UV Breakdown: O3O2 + O then O + O O2or O + O2O3

5. Creation of a CFC (chlorofluorocarbon) Methane A CFC is a totally manmade molecule. It is extremely stable and so does NOT breakdown in the troposphere. It spends approximately 20 years in the troposphere trapping IR and releasing heat thus contributing to global warming before it travels to the stratosphere.

6. Destruction of Stratospheric Ozone UV Breakdown of CFC: CFCl3CFCl2 + Cl Breakdown of Ozone: Cl + O3ClO + O2 then ClO + O O2 + Cl This final reaction leaves the chlorine radical free to attack more ozone molecules. ONE chlorine atom can destroy over 100,000 ozone molecules! With the stratospheric ozone layer only amounting to approximately 1-3 mm (if all ozone molecules were ‘squished’ together) that is serious!

7. Formation of the Ozone ‘Hole’ • During the winter over Antarctica (July) a polar • vortex forms • The polar air mass in the stratosphere becomes • separated from other air masses. • The temperature drops leading to the stratospheric • air trapped in the vortex becoming very cold. • In this cold vortex, polar stratospheric clouds (PSCs) • made up of ice crystal form. • HCl and ClONO2 cling to the surfaces of the clouds. • The CFC's react with the HCl and ClONO2 on the • ice, creating Cl2, ClONO2, & HOCl.  • When the sun returns in spring (October) the • chlorine compounds are attacked by UV releasing • the Cl atoms to attack ozone.  • Ozone densities drop rapidly (creating the ‘hole’), • until the polar vortex breaks up, releasing the ozone • depleted air to move away from the polar • region.  The ozone loss is felt globally!

8. Key: ------ Northern Hemisphere ___ Equator ___ Antarctica ___ Average

9. The Ozone ‘Hole’ over the Antarctic was first discovered in the 1970’s by Rowland and Molina. They proposed that CFCs were the cause. In 1987 the Montreal Protocol was enacted by many countries of the world. This agreement said that all countries would limit their CFC production to 50% by 2010. This was because CFCs were used in air conditioning, refrigeration, blowing agents for styrofoam, propellants for aerosols (hairsprays, etc), and a cleaning solution for microchips, etc. It was thought that the formation of an ozone hole was unique to Antarctica due to the intense cold, polar vortex, and polar stratospheric clouds. An Ozone ‘Hole’ was discovered over the northern hemispheric pole in 1992. This led to a total phase out of ALL CFCs by 1996. The replacements for CFCs (the HCFCs and HFCs) have been found to destroy stratospheric ozone.

10. 3 UV Group Wavelengths: • UV-A: closest wavelength to visible light. ALL of UV-A enters the troposphere and can cause mutations. • UV-B: some of UV-B (closer to UV-A) will enter the troposphere and can cause mutations. The other part of UV-B (closer to UV-C) is absorbed by stratospheric O3 and doesn’t enter the troposphere. When CFCs destroy stratospheric O3 it is more of the UV-B that enters the troposphere. • UV-C: wavelengths furthest from visible light. ALL of UV-C is absorbed by stratospheric O3 and doesn’t enter the troposphere.

11. Effects from Stratospheric Ozone Depletion • Increased sunburns, skin cancers (especially melanomas), • and cataracts in humans • Increased cataracts in outdoor animals • Increased suppression of the body’s immune system • Reduced yield of crops due to genetic alteration (mutation) • or reduced photosynthesis • Reduced phytoplankton numbers due to UV death • (decreased photosynthesis for uptake of CO2 and also • decreased O2 in atmosphere) • Decreased aquatic food supplies and food chain due to • reduced phytoplankton numbers

12. Effects from Stratospheric Ozone Depletion (cont.) • Decreased population of aquatic species (mostly • zooplankton) from increased UV death • Decreased photosynthesis for some tree species reducing • uptake of CO2 amounts thus increasing global warming • More acid deposition from increased amounts of HNO3 • from stratospheric reactions • Increased photochemical smog from increased UV • molecular reactions • Degradation of outdoor paints and plastics from UV • exposure • Accelerated global warming due to decreased ocean • uptakes of CO2 by phytoplankton

13. 3 types of skin cancer: • Malignant Melanoma – develops from a mole or blemish involving melanocyte cells. It can metastasize and spread throughout the body. It is the most deadly of all skin cancers. • Sqamous – develops from the squamous cells in the epidermis. It can metastasize but can be cured if caught early. • Basal – develops from the basal cells in the epidermis. It develops slowly and is ~100% curable if caught early. • How to protect yourself from sunburn & skin cancers • Stay out of the direct sun from 10 am – 3 pm • Don’t use tanning beds or sun lamps (the new SAD lamps • don’t include UV radiation) • Wear clothing that has a tight weave when in the sun. • Wear a wide-brimmed hat • Wear sunglasses that protect against both UV-A and UV-B

14. CFCs have been banned since 1996. Any remaining stock was allowed to be sold. Since it lingers in the troposphere for 20 years before rising into the stratosphere it will continue to destroy ozone molecules for years to come. Stratospheric ozone levels should return to 1980 levels by 2050 and then back to 1950 levels by 2100.