19-4 How Have We Depleted O3 in the Stratosphere and What Can We Do?

19-4 How Have We Depleted O3 in the Stratosphere and What Can We Do? Opportunities this weekend: Free Park Entrance to National Parks Yosemite Facelift Turlock Shines

Protectant Pollutant

19-4 How Have We Depleted O3 in the Stratosphere and What Can We Do?

19-4 How Have We Depleted O3 in the Stratosphere and What Can We Do? Concept 19-4A Widespread use of certain chemicals has reduced ozone levels in the stratosphere, which allows for more harmful ultraviolet radiation to reach the earth’s surface. Concept 19-4B To reverse ozone depletion, we must stop producing ozone-depleting chemicals and adhere to the international treaties that ban such chemicals.

Our Use of Certain Chemicals Threatens the Ozone Layer Ozone (O3) Layer Absorbs 95% of UV radiation from the sun. Absorption results in warming of stratosphere Ozone Thinning Seasonal depletion in the stratosphere Antarctica and Arctic 1930: Midgely Discovered the first CFC (“Dream” chemical for AC, propellants in cans, etc.) 1984: Rowland and Molina CFCs were depleting O3

Science Focus: Rowland and Moline—A Scientific Story of Courage and Persistence Research CFCs are persistent in the atmosphere Rise into the stratosphere over 11-20 years Break down under high-energy UV radiation Halogens (Cl, F, Br, I) produced accelerate the breakdown of O3 to O2 Each CFC molecule can last 65-385 years 1988: DuPont stopped producing CFCs 1995: Roland & Moline won Nobel Prize in chemistry

Global Average Total Ozone Values in the Stratosphere from 1979–2005

Natural Capital Degradation: Massive Ozone Thinning over Antarctica in 2006 Biggest “hole” on record

FREE RADICAL Summary of Reactions CFCl3 + UV → Cl + CFCl2 ClO + O → Cl + O2 Repeated many times Cl + O3 → ClO + O2 Summary of Reactions CFCl3 + UV → Cl + CFCl2 Sun Ultraviolet light hits a chlorofluorocarbon (CFC) molecule, such as CFCl3, breaking off a chlorine atom and leaving CFCl2. UV radiation FREE RADICAL Cl C Cl Cl F C Cl Cl F Cl Once free, the chlorine atom is off to attack another ozone molecule and begin the cycle again. Cl O O O The chlorine atom attacks an ozone (O3) molecule, pulling an oxygen atom off it and leaving an oxygen molecule (O2). O Ozone O O A free oxygen atom pulls the oxygen atom off the chlorine monoxide molecule to form O2. Figure 19.D Simplified summary of how chlorofluorocarbons (CFCs) and other chlorine-containing compounds can destroy ozone in the stratosphere faster than it is formed. Note that chlorine atoms are continuously regenerated as they react with ozone. Thus, they act as catalysts—chemicals that speed up chemical reactions without being used up by the reactions. Bromine atoms released from bromine-containing compounds that reach the stratosphere also destroy ozone by a similar mechanism. O O O O Cl O O O O The chlorine atom and the oxygen atom join to form a chlorine monoxide molecule (ClO). Cl O O Fig. 19-D, p. 525

Why Should We Worry about Ozone Depletion? Damaging UV-A and UV-B radiation Increase eye cataracts and skin cancer Impair or destroy phytoplankton Significance?

Figure 19.20 Science: expected effects of decreased levels of ozone in the stratosphere (Concept 19-4A). Question: Which three of these effects do you think are the most threatening? Why? Stepped Art Fig. 19-20, p. 524

Science Focus: Skin Cancer Squamous cell carcinoma Basal cell carcinoma Melanoma Effect of UV-B radiation How safe are tanning salons?

Ultraviolet A Ultraviolet B Thin layer of dead cells Squamous cells Epidermis Basal layer Sweat gland Melanocyte cells Dermis Blood vessels Basal cell Hair This long-wavelength (low-energy) form of UV radiation causes aging of the skin, tanning, and sometimes sunburn. It penetrates deeply and may contribute to skin cancer. This shorter-wavelength (high-energy) form of UV radiation causes sunburn, premature aging, and wrinkling. It is largely responsible for basal and squamous cell carcinomas and plays a role in malignant melanoma. Ultraviolet A Ultraviolet B Figure 19.E Structure of the human skin and the relationships between ultraviolet (UV-A and UV-B) radiation and the three types of skin cancer. (Data and photos from the Skin Cancer Foundation) Squamous Cell Carcinoma Basal Cell Carcinoma Melanoma Stepped Art Fig. 19-E, p. 526

Figure 19.E Structure of the human skin and the relationships between ultraviolet (UV-A and UV-B) radiation and the three types of skin cancer. (Data and photos from the Skin Cancer Foundation) Fig. 19-E (2), p. 526

We Can Reverse Stratospheric Ozone Depletion Stop producing all ozone-depleting chemicals 60–100 years of recovery of the O3 layer 1987: Montreal Protocol Worldwide ban on CFC’s Ozone protocols: prevention is the key

We Can Reverse Stratospheric Ozone Depletion Substitutes for CFCs are available More are being developed HCFC-22 Substitute chemical May still be causing ozone depletion

We Can Reverse Stratospheric Ozone Depletion http://www.youtube.com/watch?v=DLHL1Xp9iDo

The Bullet we Dodged by Working Together What Could Have Been w/o CFC Ban http://earthobservatory.nasa.gov/Features/WorldWithoutOzone/page2.php

The Bullet we Dodged by Working Together What Could Have Been w/o CFC Ban http://earthobservatory.nasa.gov/Features/WorldWithoutOzone/page2.php

The Bullet we Dodged by Working Together What Will Be… CURED! http://earthobservatory.nasa.gov/Features/WorldWithoutOzone/page2.php