PowerPoint ® Lecture prepared by Gary A. Beluzo A REDUCTION IN ATMOSPHERIC OZONE Let the Sunshine In 14
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
Copyright © 2007 McGraw-Hill Publishing Company 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
Copyright © 2007 McGraw-Hill Publishing Company The Atmosphere The atmosphere provides many environmental services Nitrogen (N 2 ) 78% Oxygen (O 2 ) 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
Copyright © 2007 McGraw-Hill Publishing Company 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 ( km) Thermosphere Figure 14.1
Copyright © 2007 McGraw-Hill Publishing Company Stratospheric Ozone 90% of ozone (O 3 ) 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. O 2 + hv O + O (14.1) O + O 2 O 3 (14.2) O 3 + hv O + O 2 (14.3)
Copyright © 2007 McGraw-Hill Publishing Company Ozone Formation
Copyright © 2007 McGraw-Hill Publishing Company 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
Copyright © 2007 McGraw-Hill Publishing Company Reduction in Stratospheric Ozone Satellites since 1979 have measured a annual decline of about 0.41 % in the entire atmosphere
Copyright © 2007 McGraw-Hill Publishing Company Antarctic October Decline
Copyright © 2007 McGraw-Hill Publishing Company An Expanded Area of Decline Figure 14.6
Copyright © 2007 McGraw-Hill Publishing Company The Halogen Depletion Hypothesis 1974 paper in Nature in which Rowland and Molina hypothesized that ozone could be reduced by chlorofluorocarbons (CFC’s) CFCl 3 + hv Cl + CFCl2 (14.4) Cl + O 3 ClO + O 2 (14.5) O + ClO Cl + O 2 (14.6) O + O 3 O 2 + O 2 (14.7)
Copyright © 2007 McGraw-Hill Publishing Company
The “Odd Nitrogen” Hypothesis Variation in solar activity “Odd Nitrogen” N 2 O 5, NO 3, etc Trapped by polar vortex NO and NO2 destroy ozone
Copyright © 2007 McGraw-Hill Publishing Company “Dynamic Uplift” Hypothesis Changes in atmospheric circulation after 1979 Upward movements of air dilutes ozone
Copyright © 2007 McGraw-Hill Publishing Company 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
Copyright © 2007 McGraw-Hill Publishing Company Effects of Less Stratospheric O 3
Copyright © 2007 McGraw-Hill Publishing Company Global Decline in Amphibians
Copyright © 2007 McGraw-Hill Publishing Company 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 % reduction turned out to be ideal
Copyright © 2007 McGraw-Hill Publishing Company Future Levels of Chlorine/Bromine Figure 14.14
Copyright © 2007 McGraw-Hill Publishing Company Declining Concentrations