Earth’s Changing Environment Lecture 5 Depletion of the Ozone Layer

The Stratospheric Ozone Layer Begins where the troposphere ends at 50,000 feet (10 miles) above the Earth’s surface. Begins where the troposphere ends at 50,000 feet (10 miles) above the Earth’s surface. The lower stratosphere is the location of most atmospheric ozone. The lower stratosphere is the location of most atmospheric ozone.

Solar UV Radiation UV Radiation is blocked by the ozone layer UV Radiation is blocked by the ozone layer But UV Radiation also forms the ozone layer. But UV Radiation also forms the ozone layer.

Solar Spectrum

Regions of the Solar Spectrum

Regions of the Solar UV Spectrum

Chapman Reactions form O3 in the Stratosphere

O3 absorbs most of the UVB radiation

These two processes form the Ozone Cycle

Depletion of the Ozone Layer

Chlorine acts as a catalyst to destroy the Ozone layer

How does Chlorine get into the Stratosphere? chlorofluorocarbons (CFCs). chlorofluorocarbons (CFCs). CFC-12 (CF2Cl2) (freon) CFC-12 (CF2Cl2) (freon) CFC-11 (CFCl3) CFC-11 (CFCl3) Have 100 year atmospheric lifetimes Have 100 year atmospheric lifetimes

Mario Molina Born in Mexico City Won Nobel Prize in 1995 In 1974 with Sherry Roland, he predicted that CFCs could destroy ozone layer

Antarctic Ozone Hole Normally, stratospheric reactions put chlorine from CFCs into inert forms (HCL and ClONO2) Normally, stratospheric reactions put chlorine from CFCs into inert forms (HCL and ClONO2) Ice crystals in these antarctic polar stratospheric clouds (PSCs) act as sites for the conversion of the inert form of chlorine to the active form of chlorine. Ice crystals in these antarctic polar stratospheric clouds (PSCs) act as sites for the conversion of the inert form of chlorine to the active form of chlorine.

Antarctic Ozone Hole Every spring, UVC radiation breaks CL 2 formed on the PSCs into atomic chlorine. This active CL causes a very sharp decrease in the concentration of ozone in the Antarctic stratosphere, an ozone hole. Every spring, UVC radiation breaks CL 2 formed on the PSCs into atomic chlorine. This active CL causes a very sharp decrease in the concentration of ozone in the Antarctic stratosphere, an ozone hole.

US Ozone Depletion

Health and Environmental Effects

The Montreal Protocol International treaty for the control on the production and consumption of ozone-depleting substances agreed on in International treaty for the control on the production and consumption of ozone-depleting substances agreed on in President Reagan signed the ratified Protocol in President Reagan signed the ratified Protocol in Copenhagen Amendment and Vienna Adjustments called for a more rapid phase out of certain ODP chemicals Copenhagen Amendment and Vienna Adjustments called for a more rapid phase out of certain ODP chemicals.

Montreal Protocol 29 countries plus the European Union signed initially 29 countries plus the European Union signed initially All have agreed to a phase-out schedule All have agreed to a phase-out schedule Globally emission of ODPs has been drastically reduced to around 10% of original levels. Globally emission of ODPs has been drastically reduced to around 10% of original levels.

EPA – Ozone Depletion Program Command and Control Strategy Command and Control Strategy Halt the production of ozone-depleting substances (ODS) Halt the production of ozone-depleting substances (ODS) Ensure refrigerants and halon fire extinguishing agents are recycled properly Ensure refrigerants and halon fire extinguishing agents are recycled properly identifying alternative to ODS identifying alternative to ODS banning the release of OD refrigerants banning the release of OD refrigerants

US Phase-out of high ODP chemicals chlorofluorocarbons (CFCs) chlorofluorocarbons (CFCs) chlorofluorocarbons (CFCs) chlorofluorocarbons (CFCs) carbon tetrachloride carbon tetrachloride carbon tetrachloride carbon tetrachloride methyl chloroform methyl chloroform methyl chloroform methyl chloroform halons halons halons

Will take 50 years to Recover