Chapter 26

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 ultravioletradiation from the sun

• A pollutant when present in the loweratmosphere

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 StratosphericOzone

• 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 thepolar winter

• Polar Vortex

– Artic air masses that in the winter become isolatedfrom the rest of the atmosphere and circulate about thepole

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

Management Issues

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

• Montreal Protocol• Collection and Reuse of CFCs• Substitutes for CFCs

– HFCs and HCFCs• Short-Term Adaptation to Ozone Depletion