botkin and keller environmental science 5e chapter 25 ozone depletion

Botkin and KellerEnvironmental Science 5e

Chapter 25

Ozone Depletion


Ozone• A form of oxygen in which three atoms of

oxygen occur together.• Chemically active and has a short average

lifetime in the atmosphere• Forms a natural layer high in the

atmosphere that protects us from harmful ultraviolet radiation from the sun

• A pollutant when present in the lower atmosphere


Ultraviolet Radiation and Ozone• Ozone Shield: Stratospheric ozone layer that

absorbs ultraviolet radiation

Ultraviolet A:– Longest length, least energetic – Can cause some damage to living cells– Transmitted to earth

Ultraviolet B:– Intermediate wavelength– Cause of Ozone Problem

Ultraviolet C:– Shortest wavelength/ Most energetic


Measurement of Stratospheric Ozone

• Dobson Unit– Commonly used to measure the concentration

of ozone


Ozone Depletion and CFCs

• Ozone depleted due to emission of CFCs

• CFCs are stable and have a long residence time in the atmosphere

• In stratosphere, release chlorine and enter into catalytic chain reaction- depletes ozone

• More UV radiation reaches lower atmosphere


Polar Stratospheric Clouds

• Clouds that form in the stratosphere during the polar winter

• Polar Vortex– Artic air masses that in the winter become isolated from

the rest of the atmosphere and circulate about the pole

– Rotates counterclockwise because of the rotation of the earth in the Southern Hemisphere


Management Issues

• Key issue is whether ozone depletion is natural or human-induced

• Montreal Protocol

• Collection and Reuse of CFCs

• Substitutes for CFCs– HFCs and HCFCs

• Short-Term Adaptation to Ozone Depletion

botkin and keller environmental science 5e chapter 25 ozone depletion

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