Physics 137 - Introduction to the Atmosphere and Weather                                                                                      Homework Key - Assignment #1
Revised - 11/02/09

1-QR5. Briefly explain the production and natural destruction of carbon dioxide near the earth's surface.  Give a reason for the increase of carbon dioxide over the past 100 years.

    Natural sources of atmospheric CO2 include the decay of vegetation, the exhalations of animals, volcanic eruptions and the combustion of fuels in naturally occurring fires. Natural removal of CO2 from the atmosphere occurs via photosynthesis. Especially important is removal in phytoplankton photosynthesis since this CO2 largely ends up dissolved in seawater. Over the past 100 years natural atmospheric sources of CO2 have been augmented by CO2 released in the burning of fossil fuels and the burning of cleared forest vegetation. The same deforestation may have slightly decreased the removal rate of CO2 from the atmosphere by photosynthesis.

1-QR7. Explain how the atmosphere "protects" inhabitants at the earth's surface.

    The atmosphere performs several functions which might be regarded as protective: (1) It absorbs most of the potentially harmful solar ultraviolet radiation which would otherwise reach the surface of the earth. This function is performed primarily by ozone (O3) in the stratosphere.  (2) It shields the earth from bombardment by micrometeoroids from interplanetary space. These burn up in the atmosphere as meteors.  (3) Its insulating properties protect the surface from wide temperature fluctuations of extremely high and low temperatures such as occur on the moon.

1-QR9. How has the composition of the earth’s atmosphere changed over time?  Briefly outline the evolution of the earth’s atmosphere.

    Immediately after the earth formed it may have had a tenuous atmosphere made of those gases which were plentiful in the solar nebula from which it formed. Hydrogen and helium were dominant with small amounts of methane, ammonia and water vapor. This primitive thin atmosphere was soon mostly lost as the light hydrogen and helium gases escaped the earth’s gravitation pull.

    Outgassing from the earth’s interior, mostly through volcanic eruptions, a process that continues today, contributed to the atmosphere which gradually accumulated and replaced the primitive atmosphere. A second possibly important contributor has been the vaporization of comets which impact the earth. The dominant gases contributed by these processes have been carbon dioxide, water vapor and nitrogen, with trace amounts of many other gases. As atmospheric pressure built upon the earth’s surface to the point that liquid water could exist, precipitation deposited most of the atmospheric water vapor in the oceans. Much carbon dioxide was dissolved in those ocean waters.

    Living organisms in their interactions with the atmosphere have been the cause of a "third atmosphere" on the earth. Plants, through photosynthesis have contributed oxygen (O2) to the atmosphere and living organisms have captured much of the earth’s carbon dioxide through the formation of carbonate sedimentary rocks, largely limestone.

1-QR10.  (a) Explain the concept of air pressure in terms of mass of air above some level.  (b) Why does air pressure always decrease with increasing height above the surface?

    (a) Pressure is a consequence of the weight of the atmosphere. A vertical column of atmosphere pushes down on whatever is beneath it with a force equal to its weight. That force divided by the cross-sectional area of the column is the force per unit area, or pressure, exerted at the base of the column. (b) As height above the surface increases, the amount of air above that level and therefore its weight and the resulting pressure all decrease.

1-QT1.  Which of the following statements relate more to weather and which relate more to climate?  (a) The summers here are warm and humid.  (b) Cumulus clouds presently cover the entire sky.  (c) Our lowest temperature last winter was -29°C (-18°F).  (d) The air temperature outside is 22°C (72°F).  (e) December is our foggiest month.  (f) The highest temperature ever recorded in Phoenixville, Pennsylvania was 44°C (111°F) on July 10, 1936.  (g) Snow is falling at the rate of 5 cm (2 in.) per hour.  (h) The average temperature for the month of January in Chicago, Illinois, is -3°C (26°F).

    (a) Climate, (b) weather, (c) climate, (d) weather, (e) climate, (f) climate, (g) weather, (h) climate.

1-QT2.  A standard pressure of 1013.25 millibars is also known as one atmosphere (1 ATM).  (a) Look at Fig. 1.9 and determine at approximately what levels you would record a pressure of 0.5 ATM and 0.1 ATM.  (b) The surface air pressure on the planet Mars is about 0.007 ATM.  If you were standing on Mars, the surface air pressure would be equivalent to a pressure observed at approximately what elevation in the Earth's atmosphere?

    (a) From Fig. 1.9:  P = 0.5 atm would occur at about h = 5.5 km and P = 0.1 atm would occur at about h = 16 km.

    (b) From Fig. 1.9:  P = 0.007 atm, the surface pressure on Mars, would occur on Earth at about h = 34 km.