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 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; absorbed by ozone –Cause of Ozone Problem Ultraviolet C: –Shortest wavelength/ Most energetic –Can break down O2 into two individual O atoms

Measurement of Stratospheric Ozone Dobson Unit –Commonly used to measure the concentration of ozone –1DU = concentration of 1 ppb O3 –most measurements in mid-latitudes –Antarctic (began 1957) October (Spring) 300 ('57) to 150 ('86) to 100 ('05) “Hole” - depletion in ozone concentration

Ozone Depletion and CFCs Ozone depleted due to emission of CFCs CFCs are stable (non-reactive) 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 Antarctic (1), Arctic (2)

Stratospheric Chlorine Chemistry 1. Cl + 03 yields ClO + O2 2. ClO + O yields Cl + 02 –Catalytic chain reaction –Can be interrupted through storage of chlorine in other compounds nitrogen dioxide methane

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 circulates about the pole cools, condenses and sinks –Rotates counterclockwise because of the rotation of the earth in the Southern Hemisphere –Clouds dissipate late spring and summer

Polar Stratospheric Clouds Type I Clouds –-78˚ C to -83˚ C –sulfuric acid particles frozen and serve as see for nitric acid Type II Clouds –below -83˚C –water vapor condenses around Type I particles –larger particles; nitric acid particles “fall-out” –facilitates O3 depleting reactions

Tropical and Mid-Latitude Ozone Depletion Ice particles in Stratosphere Sulfuric acid aerosols (volcanic eruptions)

Environmental Effects Damage to earth's food chains on land and oceans Damage to human health –skin cancers, cataracts, suppressed immune systems Decrease in ocean productivity –phytoplankton –CO2 sink Food crops (if more widespread)

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