Ozone Depletion

OZONE DEPLETION IN THE STRATOSPHERE Less ozone in the stratosphere allows for more harmful UV radiation to reach the earth’s surface. The ozone layer keeps about 95% of the sun’s harmful UV radiation from reaching the earth’s surface. Chlorofluorocarbon (CFCs) have lowered the average concentrations of ozone in the stratosphere.

A combination of low temperatures and elevated chlorine and bromine concentrations are responsible for the destruction of ozone in the upper stratosphere thus forming a “hole”. (Kerr, 1987) www.met.sjsu.edu/~cordero/ education/education.htm

Ultraviolet light hits a chlorofluorocarbon (CFC) molecule, such as CFCl3, breaking off a chlorine atom and leaving CFCl2. Sun Cl Once free, the chlorine atom is off to attack another ozone molecule and begin the cycle again. UV radiation A free oxygen atom pulls the oxygen atom off the chlorine monoxide molecule to form O2. The chlorine atom attacks an ozone (O3) molecule, pulling an oxygen atom off it and leaving an oxygen molecule (O2). Figure 20.18 Natural capital degradation: 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 reaction. Bromine atoms released from bromine-containing compounds that reach the stratosphere also destroy ozone by a similar mechanism. The chlorine atom and the oxygen atom join to form a chlorine monoxide molecule (ClO). Summary of Reactions CCl3F + UV Cl + CCl2F Cl + O3 ClO + O2 Cl + O Cl + O2 Repeated many times Fig. 20-18, p. 486

OZONE DEPLETION IN THE STRATOSPHERE Ozone thinning: caused by CFCs and other ozone depleting chemicals (ODCs). Increased UV radiation reaching the earth’s surface from ozone depletion in the stratosphere is harmful to human health, crops, forests, animals, and materials such as plastic and paints.

• Immune system suppression Natural Capital Degradation Effects of Ozone Depletion Human Health • Worse sunburn • More eye cataracts • More skin cancers • Immune system suppression Food and Forests • Reduced yields for some crops • Reduced seafood supplies from reduced phytoplankton • Decreased forest productivity for UV-sensitive tree species Wildlife • Increased eye cataracts in some species • Decreased population of aquatic species sensitive to UV radiation • Reduced population of surface phytoplankton Figure 20.21 Natural capital degradation: expected effects of decreased levels of ozone in the stratosphere. QUESTION: Which five of these effects do you think are the most important? • Disrupted aquatic food webs from reduced phytoplankton Air Pollution and Materials • Increased acid deposition • Increased photochemical smog • Degradation of outdoor paints and plastics Fig. 20-21, p. 488 Global Warming • Accelerated warming because of decreased ocean uptake of CO2 from atmosphere by phytoplankton and CFCs acting as greenhouse gases

Squamous Cell Carcinoma 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 Thin layer of dead cells Hair Squamous cells Epidermis Basal layer Sweat gland Melanocyte cells Dermis Basalcell Blood vessels Figure 20.22 Science: 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 Fig. 20-22, p. 489

Montreal Protocol on Substances That Deplete the Ozone Layer Proposed in 1987 and put into action in 1989. Considered to be the most successful international agreement on behalf of the environment Stopped production of all CFC’s except in a few cases where there aren’t substitutes (ie. some types of medical inhalers) Use of some substitutes is problematic however as they don’t damage ozone but are Greenhouse gases (HFC’s, etc)

The Environmental Protection Agency (EPA) Responsible for enforcing the Montreal Protocol within the U.S. The EPA has several programs in place; Regulating and enforcing on-road car and truck air-conditioning systems Regulating most air-conditioning and refrigeration appliances Technician certification Service equipment

Signs of Recovery??? There have been some signs of recovery 1997 satellite showed a decline of several known ozone- depleting gases Satellite images show some slowing down of ozone loss However…. Antarctica - Dec. 2005 Recovery is slow www.coolantarctica.com/. ../ozone_hole.htm

As of 2014, stratospheric ozone has held steady and/or improved. Levels of CFC’s remaining in atmosphere have continued to drop. Appears to be a success story in the making!!