1. Chapter 3 Earth’s Modern Atmosphere Robert W. Christopherson Charlie Thomsen © 2012 Pearson Education, Inc.

3. Earth’s Modern Atmosphere Topics in this chapter: Atmospheric Composition, Temperature, and Function Atmospheric profile Atmospheric composition Atmospheric temperature Atmospheric Components Air pollution Ozone Depletion

4. Atmospheric Composition, Temperature, and Function The air in the atmosphere is a mix of various gases. The earth’s principle atmosphere extends to approx 480 kms above the surface of the earth, but the depth varies at different latitudes. Beyond that is the exosphere where the atmospheric gases are very rarified.

5. Atmospheric Profile Atmosphere extends to 32,000 km (20,000 mi) from surface Thermosphere is at 480 km (300 mi)—top of the principal atmosphere Three criteria to examine atmosphere Composition Temperature Function

6. Atmospheric Profile In order to better understand the atmosphere and it’s composition we study the layers that make it up. These layers are defined according to their temperature, composition and function. The atmosphere has mass (weight) and as a result exerts pressure on the earth. This is known as atmospheric pressure and is an important tool in understanding and predicting climate. Average atmospheric pressure is 1kg/cm 2 Atmospheric pressure decreases outwards from the earth’s surface.

7. Atmospheric Pressure © 2012 Pearson Education, Inc. Figure 3.3

8. Atmospheric Gases Nitrogen: 78% Predominantly volcanic in origin. It forms an important building block of organic matter. In animals it is consumed indirectly through compounds in food. Oxygen: 21% Respiration Combustion Decomposition Carbon dioxide: 0.039% (increasing due to anthropogenic factors) Natural greenhouse effect / atmospheric heat balance Used by plants during photosynthesis Argon: 0.934% Inert Trace gases eg. water vapour: amount variable

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11. Atmospheric Composition Heterosphere – outer atmosphere From 80 km outward, to thermopause. Layers of gases are not evenly mixed. Homosphere – inner atmosphere Earth’s surface to 80 km. Gases evenly blended Consists of the inner three layers of the atmosphere.

12. Layers of the Atmosphere: Atmospheric Temperature Thermosphere Roughly same as heterosphere 80 km (50 mi) outward Gases rarified Temperature increases sharply with altitude, but actual heat is low due to the rarified gases. Upper limit is the thermopause which may vary in altitude, determined by solar activity from 480kms above the earth to 250 kms.

13. Layers of the Atmosphere: Atmospheric Temperature (contd.) Mesosphere Part of the homosphere 50 to 80 km above the earth Temperature decreases with an increase in altitude, forming the coldest part of the atmosphere at the mesopause -90˚C Can contain cosmic or meteoric dust, if ice crystals form on this it can create a noctilucent cloud.

14. Layers of the Atmosphere: Atmospheric Temperature (contd.) Stratosphere 18 to 50 km Contains the ozone layer. This layer absorbs harmful ultra-violet radiation from the sun. Temperatures increase with altitude throughout this layer due to the absorption of the ozone layer.

15. Atmospheric Temperature Troposphere Lowest layer of the atmosphere Surface to average altitude of 18 km, although this differs dramatically between the equator and the poles. Contains 90% mass of atmospheric gas The average temperature at the top of this layer is -57˚C, but this also varies. Normal lapse rate – average cooling (with altitude) at rate of 6.4 C°/km. Environmental lapse rate – actual local lapse rate (this will be discussed more in chaps 7 and 8. All biosphere processes occur in this layer. All weather occurs in this layer. The tropopause forms the upper boundary of water and water vapour in the atmosphere.

16. Profile of Atmosphere © 2012 Pearson Education, Inc. Figure 3.2

17. © 2012 Pearson Education, Inc. CO 2 increase 1958–2010 Figure 3.4

18. Temperature Profile © 2012 Pearson Education, Inc. Figure 3.5

19. Atmospheric Function Ionosphere (mesosphere and thermosphere) Absorbs cosmic rays, gamma rays, X-rays, some UV rays Auroras occur in this layer. Ozonosphere Part of stratosphere Ozone (O 3 ) absorbs UV energy and converts it to heat energy This process converts most of the harmful ultraviolet radiation to longer wavelengths effectively ‘safeguarding’ the earth from harmful radiation.

20. Protective Atmosphere Figure 3.6 © 2012 Pearson Education, Inc.

21. Ozone Depletion Stratospheric ozone: a concentration of O 3 gas in the stratosphere layer of the atmosphere. This layer absorbs the harmful ultra-violet radiation from the sun, preventing it from reaching the earth. Ozone loss in this layer is being caused by chloroflurocarbons (CFCs). This is a synthetic molecule composed of chlorine, fluorine and carbon. It was manufactured for use in refrigeration, solvents, aerosols and various other items. This molecule is stable under the earth’s surface conditions however when transported to the stratosphere the intense ultraviolet light breaks it down and liberates the chlorine.

22. Ozone Depletion (contd.) The chlorine molecule causes a complex set of chemical reactions that breaks down the O 3 molecule leaving O 2 molecules. The effect is severe as one chlorine atom decomposes more than 100 000 ozone molecules. These chlorine atoms remain for between 40 and 100 years in the ozone and as a result the effects are extensive. This has caused extensive loss of ozone, and what is commonly termed ozone holes particularly over the arctic and Antarctic.

23. Ozone Depletion (contd.) Depleted ozone causes an increase in UV radiation at the surface particularly dangerous to humans as it is cancer causing radiation. Stratospheric ozone depletion was it’s worst ever above Antarctica in Sept.- Nov. 2006, and each year it widens and deepens although the chemicals which cause this depletion are not being produced or utilised much anymore. The Montreal protocol was first signed in 1987 with initiatives to reduce and eliminate CFC production. This was successful, and has been amended and strengthened since, but the lifespan of the chlorine molecules in the ozone layer is still problematic.

24. Antarctic Ozone Hole 2008 Figure 3.1.1 © 2012 Pearson Education, Inc.

25. ClO and O 3 Figure FS 3.1.2

27. Variable Atmospheric Components Air pollution can be caused by natural and anthropogenic factors: Natural sources Natural factors that affect air pollution Anthropogenic pollution

28. Natural Sources of Air Pollution Large amounts of chemical and particulate matter from volcanoes. eg. 1991 Mt. Pinatubo eruption which ejected nearly 20 million tons of sulfur dioxide into the stratosphere. Wild fires: soot, ash, and gasses (nitrogen oxides, carbon monoxide).

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30. Southern California Wildfires Figure 3.7a © 2012 Pearson Education, Inc.

31. Anthropogenic Pollution Anthropogenic air pollution tends to be worst in urban areas, although agriculture and human induced fires also cause air pollution in rural areas. Many of these chemical pollutants are produced through combustion of fossil fuels in transport and electricity production. Carbon monoxide: transportation, biomass burning.

32. Anthropogenic Pollution (contd.) Photochemical smog: transportation, the outputs react with sunlight to produce dangerous air pollutants such as ozone, and nitric acid. Industrial smog and sulfur oxides: energy production using coal, producing sulphur dioxide, sulphur trioxide and sulphate aerosols all of which are dangerous to health and corrode metals. Particulates: haze, smoke and dust. Can cause scarring in lung tissue and fibrosis.

33. Air Pollution Figure 3.14

34. Natural Factors That Affect Air Pollution Certain natural factors make the effects of pollutants worse: Winds: transporting pollutants and dust. Local and regional landscapes: mountains and valleys can trap and concentrate pollutants. Temperature inversion: where normal temperature decrease with altitude is reversed and becomes a temperature increase with altitude pollution is trapped and concentrated below this layer.

35. Temperature Inversion Figure 3.9 © 2012 Pearson Education, Inc.

36. Photochemical Smog Figure 3.10 © 2012 Pearson Education, Inc.

37. Robert W. Christopherson Charlie Thomsen Geosystems 8e An Introduction to Physical Geography End of Chapter 3 © 2012 Pearson Education, Inc.