PowerPoint ® Lecture prepared by Gary A. Beluzo A REDUCTION IN ATMOSPHERIC OZONE Let the Sunshine...

PowerPoint® Lecture prepared by Gary A. Beluzo

A REDUCTION IN ATMOSPHERIC OZONE Let the Sunshine In

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Copyright © 2007 McGraw-Hill Publishing Company

STUDENT LEARNING OUTCOMES

• Explain why temperature rises or falls with altitude in different layers of the atmosphere.

• Compare and contrast three hypotheses for the depletion of stratospheric ozone and how the scientific method was used to choose among them.

• Compare and contrast the depletion of stratospheric ozone above the northern and southern poles.

• Describe how a reduction in stratospheric ozone affects organisms that live in either marine or terrestrial ecosystems.

• Describe the role of scientific information in the process that culminated in agreements to end the production of CFCs

After reading this chapter, students will be able to


An Environmental Success Story

• Spring 1986 scientists announced the atmosphere above South Pole had 40% less ozone (O3)

• But in 1974, Rowland and Molina hypothesized that CFCs could destroy the ozone layer

• Environmentalists argued that life could be wiped out

• Industry responded that CFCs were critical to modern life

• Need for cooperation among consumers, industry, government


The Atmosphere

• The atmosphere provides many environmental services

• Nitrogen (N2) 78%

• Oxygen (O2) 21%

• Trace Gases (mostly Ar) 1%

• CO2 is about 0.038% or 380 ppm and now increasing 2.2 ppm/year

CO2 has increased 20% since 1959 whereas oxygen has varied less than 0.03% over the last 50 years


Layers of the Atmosphere• Troposphere (extends up

to altitude of 8 km in polar and 15 km in tropics

• Lapse rate (-6.5º C/km)

• Tropopause keeps water vapor in the troposphere

• Stratosphere (20-50 km)

• Mesosphere (50-100 km)

• Thermosphere

Figure 14.1


Stratospheric Ozone• 90% of ozone (O3) is in the stratosphere

• Solar energy powers the formation of ozone

• The amount of single atom oxygen (O) determines rate at which ozone is formed.

O2 + hv O + O (14.1)

O + O2 O3 (14.2)

O3 + hv O + O2 (14.3)


Ozone Formation


Distribution of Ozone

• Ozone is measured in dobson units (DU)

• 100 DU would be a “pile” 1mm thick at sea level and 0 degrees C.

• There are about 300 DU of ozone, which is equivalent to a pile of molecules 3 mm thick.

• Most ozone is formed near the equator

• Distributed throughout stratosphere by global air circulation

• The result is greatest concentration at mid latitudes, especially in northern hemisphere


Reduction in Stratospheric Ozone

• Satellites since 1979 have measured a annual decline of about 0.41 % in the entire atmosphere


Antarctic October Decline


An Expanded Area of Decline

Figure 14.6


The Halogen Depletion Hypothesis• 1974 paper in Nature in which Rowland and Molina

hypothesized that ozone could be reduced by chlorofluorocarbons (CFC’s)

CFCl3 + hv Cl + CFCl2 (14.4)

Cl + O3 ClO + O2 (14.5)

O + ClO Cl + O2 (14.6)

O + O3 O2 + O2 (14.7)


The “Odd Nitrogen” Hypothesis

• Variation in solar activity

• “Odd Nitrogen” N2O5, NO3, etc

• Trapped by polar vortex

• NO and NO2 destroy ozone


“Dynamic Uplift” Hypothesis

• Changes in atmospheric circulation after 1979

• Upward movements of air dilutes ozone


Which is Correct?

• Scientists tested each hypothesis

• Fly plane into and out of reduced ozone area

• No increased levels of “Odd Nitrogen”

• Nitrous oxide levels low

• Relationship between ozone and ClO was striking

Figure 14.10


Effects of Less Stratospheric O3


Global Decline in Amphibians


Policies to Restore Ozone Layer

• Political Response is Environmental Success

• If halogen depletion correct: CFCs had to be banned

• If halogen depletion was false: banning CFCs would impair the global economy

• Economic and environmental threat created deadlock

• NASA and WMO published “blue books” in 1986

• Montreal Protocol in 1987

• 50% reduction turned out to be ideal


Future Levels of Chlorine/Bromine

Figure 14.14


Declining Concentrations

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