1. Ch. 23 The Atmosphere Ch. 23.1 Characteristics of the Atmosphere

2. Composition of the Atmosphere Most abundant elements—nitrogen, oxygen, and argon. Most abundant elements—nitrogen, oxygen, and argon. Most abundant compounds—carbon dioxide and water vapor. Most abundant compounds—carbon dioxide and water vapor. Water vapor is added through evaporation and transpiration, and removed through condensation and precipitation. Its concentration varies from 4% to less than 1%. Water vapor is added through evaporation and transpiration, and removed through condensation and precipitation. Its concentration varies from 4% to less than 1%.

3. Ozone—a form of oxygen (O 3 instead of O 2 ) that exists in the upper atmosphere—important because it absorbs harmful ultraviolet rays. Ozone—a form of oxygen (O 3 instead of O 2 ) that exists in the upper atmosphere—important because it absorbs harmful ultraviolet rays. Ozone can be destroyed by human pollutants such as chlorofluorocarbons (CFC’s). Ozone can be destroyed by human pollutants such as chlorofluorocarbons (CFC’s). Also present is atmospheric dust—suspended mineral particles from the land and salt crystals from the ocean. Also present is atmospheric dust—suspended mineral particles from the land and salt crystals from the ocean.

4. 78% Nitrogen 78% Nitrogen 21% Oxygen 21% Oxygen 0.9% Argon 0.9% Argon 0.1% other (including carbon dioxide) 0.1% other (including carbon dioxide)

5. Oxygen in the Atmosphere Oxygen is both removed and replaced in the atmosphere at a constant rate, so the percentage of oxygen remains in a state of balance. Oxygen is both removed and replaced in the atmosphere at a constant rate, so the percentage of oxygen remains in a state of balance. Removed by: animals, bacteria, plants, burning of fuels and forests, and the weathering of rocks. Removed by: animals, bacteria, plants, burning of fuels and forests, and the weathering of rocks. Replaced by: land and ocean plants through photosynthesis. Replaced by: land and ocean plants through photosynthesis.

7. Nitrogen in the Atmosphere The nitrogen cycle maintains a constant amount of nitrogen in the atmosphere. The nitrogen cycle maintains a constant amount of nitrogen in the atmosphere. Nitrogen moves from the air, to the soil, to plants and animals, and again back to the air. Nitrogen moves from the air, to the soil, to plants and animals, and again back to the air. Nitrogen-fixing bacteria convert atmospheric nitrogen into useful nitrogen compounds taken up by plants, which are then eaten by animals. Nitrogen-fixing bacteria convert atmospheric nitrogen into useful nitrogen compounds taken up by plants, which are then eaten by animals. Denitrifying bacteria release nitrogen back to the air when plants and animals decay or excrete waste. Denitrifying bacteria release nitrogen back to the air when plants and animals decay or excrete waste.

9. Atmospheric Pressure Atmosphere is held by Earth’s gravity. Atmosphere is held by Earth’s gravity. 99% of atmosphere’s mass is within 32 km of the surface. 99% of atmosphere’s mass is within 32 km of the surface. Remainder extends upwards towards space for hundreds of kilometers, getting thinner with increasing altitude. Remainder extends upwards towards space for hundreds of kilometers, getting thinner with increasing altitude. Weight of the atmosphere presses on the surface. Weight of the atmosphere presses on the surface.

10. A column of air one square inch at its base, at sea level, and extending upward to the upper edge of the atmosphere, weighs 14.7 pounds. A column of air one square inch at its base, at sea level, and extending upward to the upper edge of the atmosphere, weighs 14.7 pounds. Force of the air on the surface can be expressed in newtons (101,325 N). Force of the air on the surface can be expressed in newtons (101,325 N). Atmospheric pressure is the ratio of the force of the air to the area of the surface on which it presses. Atmospheric pressure is the ratio of the force of the air to the area of the surface on which it presses. Atm. press. decreases with increasing altitude. Atm. press. decreases with increasing altitude.

11. Mercurial Barometer Barometers are instruments that measure atmospheric pressure. Barometers are instruments that measure atmospheric pressure. In a mercurial barometer, the atmospheric pressure presses on a bowl of mercury and forces it up a tube. In a mercurial barometer, the atmospheric pressure presses on a bowl of mercury and forces it up a tube. At sea level, mercury would be forced up the tube to an average height of 760 mm. At sea level, mercury would be forced up the tube to an average height of 760 mm.

13. Aneroid Barometer Aneriod—without liquid. Aneriod—without liquid. Contains sealed metal container at a vacuum. Contains sealed metal container at a vacuum. Sides of container flex inwards or outwards depending on air pressure. Sides of container flex inwards or outwards depending on air pressure. Pointer attached to container. It moves along a scale, and indicates the atmospheric pressure. Pointer attached to container. It moves along a scale, and indicates the atmospheric pressure.

14. Layers of the Atmosphere Pressure gradually decreases with increasing altitude, but temperature shows distinct differences with increasing altitude. Pressure gradually decreases with increasing altitude, but temperature shows distinct differences with increasing altitude. Temp. differences are due to the way solar energy is absorbed as it moves downward through the atmosphere. Temp. differences are due to the way solar energy is absorbed as it moves downward through the atmosphere. Four distinct layers based on temperature differences. Four distinct layers based on temperature differences.

15. The Troposphere Layer closest to the earth, in which nearly all weather occurs. Layer closest to the earth, in which nearly all weather occurs. Almost all water vapor and carbon dioxide found in the troposphere. Almost all water vapor and carbon dioxide found in the troposphere. Temp. decreases with increasing altitude, due to increasing distance from earth’s surface (and distance from the warming effect of sunlight absorbed by earth’s surface). Temp. decreases with increasing altitude, due to increasing distance from earth’s surface (and distance from the warming effect of sunlight absorbed by earth’s surface).

16. Rate of temperature decrease is about 6.5° C per km. Rate of temperature decrease is about 6.5° C per km.

17. The Stratosphere Extends upward from the troposphere to a height of about 50 km. Extends upward from the troposphere to a height of about 50 km. Contains most of the ozone in the atmosphere (the ozone layer). Contains most of the ozone in the atmosphere (the ozone layer). About -60° C at its base, but temp. begins rising in upper stratosphere as altitude increases…due to direct absorption of solar energy by ozone. About -60° C at its base, but temp. begins rising in upper stratosphere as altitude increases…due to direct absorption of solar energy by ozone.

18. The Mesosphere Layer above the stratosphere, extending to an altitude of about 80 km. Layer above the stratosphere, extending to an altitude of about 80 km. Temperature decrease as altitude increases…the coldest layer, dropping to about -90° C. Temperature decrease as altitude increases…the coldest layer, dropping to about -90° C. Very thin air, but thick enough to burn up most meteors. Very thin air, but thick enough to burn up most meteors.

19. The Thermosphere Layer above the mesosphere. Temperature increases steadily with altitude, due to absorption of short wavelength solar energy by oxygen and nitrogen. Layer above the mesosphere. Temperature increases steadily with altitude, due to absorption of short wavelength solar energy by oxygen and nitrogen. Although very high temperatures (over 2000°C recorded), air is so thin and its molecules so far apart that little heat is transferred. Although very high temperatures (over 2000°C recorded), air is so thin and its molecules so far apart that little heat is transferred. Upper boundary of thermosphere not accurately determined. Upper boundary of thermosphere not accurately determined.

20. The Ionosphere Within lower region of thermosphere (80 – 550 km). Within lower region of thermosphere (80 – 550 km). Solar rays strip electrons from gas molecules, forming ions and free electrons. Solar rays strip electrons from gas molecules, forming ions and free electrons. There are four layers of the ionosphere. There are four layers of the ionosphere. Free electrons can reflect radio waves back to earth. Free electrons can reflect radio waves back to earth.

21. The Exosphere Region of atmosphere where it blends into the vacuum of interplanetary space. Region of atmosphere where it blends into the vacuum of interplanetary space. Extends thousands of km above the surface. Extends thousands of km above the surface.

22. Air Pollution Substances in the atmosphere harmful to people, animals, plants, or property. Substances in the atmosphere harmful to people, animals, plants, or property. Results mainly from the burning of fossil fuels. Results mainly from the burning of fossil fuels. Gases from fossil fuels combine with water to form acid rain, which kills plants and fish. Gases from fossil fuels combine with water to form acid rain, which kills plants and fish. Sometimes, cold air becomes trapped under warm air…this condition is a temperature inversion. The air is unable to disperse, and pollutants build up (common in Los Angeles). Sometimes, cold air becomes trapped under warm air…this condition is a temperature inversion. The air is unable to disperse, and pollutants build up (common in Los Angeles). The result is smog (smoke and fog). The result is smog (smoke and fog).