Stratospheric Ozone Depletion ES 110: Introduction to Environmental Science 3-5 Sep 2008

Ozone Depletion What is the “ozone layer?” How does it protect us? How did it come about?

Evolution of the Ozone Layer Early planet history: –no ozone present –UV light directly hit planet’s surface –Oceans provided only refuge from UV radiation

Oxygen in the Atmosphere O O +O 3 (ozone) UV radiation + O2O2 O + O2O2

O + O2O2 O2O2 O2O2 + + O 3 (ozone) heat O + O 3 ( ozone ) O + O2O2 UV O 3 (ozone) +

Causes of Ozone destruction Polar stratospheric clouds Volcanic eruptions

Dynamic Equilibrium creation of ozone breakdown of ozone

Anthropogenic Ozone Depletion creation of ozone breakdown of ozone

Modern Impacts to Ozone I Chlorofluorocarbons (CFCs) What are they? How do they impact the ozone layer?

Development of CFCs 1928:DuPont scientists develop CFCs “ideal compounds” for refrigerants and propellants WHY??

CFCs as Refrigerants vs. CFCs - Non-flammable - Non-toxic - Trap heat (good insulators!) - Inexpensive - Light -Extremely stable, inert Traditional Refrigerants (ammonia, sulfur dioxide, methyl chloride) - Highly volatile - Caustic and toxic - Remove heat through vaporization of liquefied gas (only adequate as refrigerants) - Expensive - Heavy (transport, storage)

Key physical characteristics of CFCs Light weight Extremely stable or “inert” CFCs likely to migrate upwards Too light to precipitate out with rainfall 5-15 years to migrate to stratosphere What are the consequences of these features?

Marketing of CFCs 1958: DuPont releases CFCs on the market commercially 1971: James Lovelock speculates that CFCs put into the atmosphere may still be present 1973: Mario Molina and F. Sherry Roland start to investigate

Original Research 1974:Rowland and Molina UV radiation + Cl F F CC F F + Cl - “free radical”

Cl - “Free Radicals”… Cl - “free radical” O 3 ( ozone ) + O2O2 ClO + + O Cl - “free radical” + O2O2 ClO

In the news… 1974:Molina and Rowland publish their hypothesis in Nature. New York Times runs front page DuPont responds with study showing that CFCs in troposphere are benign

Location of Stratosphere Thermosphere Exosphere Troposphere Mesosphere Stratosphere 10 km 40 km 50 km 300 km 400 km

Based on theory alone… 1979:The FDA, EPA ban non-essential uses of CFCs ! First time substance EVER banned in US without direct proof of harm 1982:20 other countries join US in ban

How do we know O 3 concentrations?

The challenge of scientific evidence British science teams in Antarctica study stratospheric ozone using weather balloons and observe: –20% reduction in ozone layer (1982) –30% reduction in ozone layer (1983) –50% reduction in ozone layer (1985) US scientists relying on new TOMS satellite measurements (Total Ozone Mapping Spectometer) observe: –No reduction (1982) –No reduction (1983) –No reduction (1984) –Finally recognize need to recalibrate equipment and validate 50% reduction in ozone layer! (1985) WHY THE SCIENTIFIC SNAFUS??

Total ozone Total ozone measured above Antarctica, in Dobson Units. From Horel and Geisler, 1996

October Average for Total Ozone over Antarctica, Based on British measurements from weather balloons

TOMS Data (corrected)

Landmark: Montreal Protocol UN hosts meeting in Montreal in Nations sign to reduce CFC use by 50% by year Developing countries’ efforts to reduce CFC use would be ‘subsidized’

Lasting impacts of Montreal Protocol… Follow up meetings result in: 1992:Industrialized nations—total ban by 2000 Developing nations—ban by 2010, with assistance from developed nations US agrees to complete phaseout by 1996; DuPont to halt production by :Rowland and Molina receive Nobel Prize Ozone loss: Extends beyond Polar regions Over US: currently 5% below normal

Why Protect the Ozone Layer? Or Negative consequences of increased UV radiation Human Health Ecological Health Economic Impacts

Skin Melanoma Incidence by State, 2004 Source: CDC United States Cancer Statistics: 2004 Incidence and Mortality.

Skin cancer Melanoma Cataracts Immune system function Increased incidence, severity and duration of infectious diseases Reduced efficacy of vaccinations Pathogens variable locally Local biodiversity variable Aquatic organisms adversely impacted Decreased biomass productivity Polar systems especially vulnerable Impacts of Ozone Depletion Human Health Ecological Health

Impacts of Ozone Depletion Economic Concerns Plastics –designed with stabilizers to withstand UV radiation of certain intensity –replacement of key medical equipment and supplies, decreased lifespan of plastics Manufacturing practices Agriculture Consumer costs and burdens

Breakdown of Sources US Nuclear Regulatory Commission 2003

Current Rate of Ozone Depletion Baseline ozone levels reduced 99% of total UV Decrease in rate of ozone depletion (since 1997) Slowing of buildup of harmful Cl - from CFCs Ozone hole is still growing, but… Models anticipate restoration of “normal” balance of ozone in stratosphere by 2050

Current Ozone Levels Sources: WOUDC, GIT, UA Huntville, Hampton U, NASA, NOAA

Location of Ozone Losses Ozone loss: Extends beyond Polar regions Over US: currently 5% below normal

Success Story What characteristics define ozone depletion “an environmental success story ?”