Chapter 22 Section 1 pages 547-554 Characteristics of the Atmosphere

What is the atmosphere? The layer of gases that surround the Earth. This mixture is called “air”. What does it do? It protects Earth’s surface from the sun’s radiation and helps to regulate the temperature of Earth’s surface.

The layers of the atmosphere

What are the most abundant elements in the air? Elements = one so------ Nitrogen Oxygen Argon Now—what are the two most abundant compounds? Carbon dioxide Water vapor-H2O

Nitrogen 78% of the atmosphere The nitrogen cycle maintains this nitrogen in the atmosphere During the cycle nitrogen moves from the air to the soil to plants and animals and then returns to the air. See the next picture:

The Nitrogen Cycle

Review Nitrogen is removed by bacteria that lives on “nodules” of legume plants. Of course they are under the soil. The bacteria are called “nitrogen-fixing” bacteria.

Remember that the bacteria change the nitrogen in the air to: Compounds that the plant can use. Animals then eat the plants and gain the nitrogen and when the animals leaves waste the nitrogen goes back into the ground and air. A dead and decaying carcass also serves this same purpose. Ocean life have a similar process of the nitrogen cycle.

Oxygen 21% of the atmosphere Natural process maintain oxygen-animals, bacteria remove a lot and plants a little. Forest fires & the burning of fuels also remove oxygen.

Oxygen would be used up if we did not have----- Plants from the ocean and land to produce oxygen during photosynthesis.

How much oxygen is produced? Exactly the amount used up = 21% What about the water vapor in the atmosphere? It comes from the oceans, lakes, streams and soil. Where else? Animal and plants during transpiration and respiration.

Water vapor enters the atmosphere and leaves via condensation and precipitation. What factors would determine what % of water vapor is in the atmosphere? Time of day, Location, & Season The composition of the atmosphere is usually given as “dry air” Why? Because the water vapor always changes. FYI-dry air has less than 1% water vapor and moist air as much as 4%.

Ozone What is it? A molecule with 3 oxygen atoms together.

Ozone lies in the upper atmosphere Why is it important to us? It absorbs harmful ultraviolet rays. Without it we would be severely sun-damaged!

Why is the ozone being depleted? CFCs-chlorofluorocarbons used to be used in refrigerators and air conditioners but have been taken out. What about particulates in the atmosphere? These are the solids like volcanic ash, ash from fires, microscopic organisms or minerals particles. Pollen and particles from meteors are also particulates.

A filter to catch Particulates Causes of particulates can also be tornadoes and windstorms. Seaspray can evaporate and leave salt in the air.

Atmospheric Pressure What holds the atmosphere close to Earth? Gravity! Because of this the air molecules are compressed together and exert force on Earth’s surface=atmospheric pressure Atmospheric pressure is exerted equally in all direction. This is a picture of “low” pressure

Why is the air thinner as we go higher? The pull of gravity is less so the air molecules are farther apart. Pressure can also change due to differences in temperatures and the amount of water vapor in the air. Again, the air molecules move farther apart with heat.

How does this change things? The farther apart the molecules are—the less pressure they can exert. Atmospheric pressure is less at sea level. Dry air is more dense that water vapor air--??How—because the water vapor molecules have less mass than nitrogen or oxygen molecules do.

From the previous pictures of molecules please understand that: The lighter water vapor molecules replace an equal number of heavier oxygen and nitrogen molecules, which makes the volume of air less dense. Cold dense air sinks-------------- Warm air rises-----

How do meteorologists measure atmospheric pressure? With a barometer. It is a sealed container with most of the air removed. This one is a fancy model of the one some of you may have made. It is an Aneroid Barometer

How does it work? Changes in the atmospheric pressure cause the sides of the container to end inward or bulge out. These changes move the pointer on the scale.

Another type of barometer is the Mercurial Barometer This works by the atmospheric pressure pressing on the liquid mercury in a well at the base of the barometer. The height of the mercury inside the tube varies with the atmospheric pressure. The greater the pressure the higher the mercury.

An aneroid barometer can also be used to measure altitude above sea level. When used in this manner it is called an “Altimeter” At high altitudes the atmosphere is less dense and exerts less pressure than at low altitudes. So, a lowered pressure reading can be interpreted as an increased altitude reading.

Layers of the atmosphere

Troposphere All weather occurs here Closest to the Earth Water vapor and CO2 in this layer Temps. Decrease as altitude increases-why? Because air in this layer is heated from below by thermal energy radiating from Earth. At the altitude of 12 km the temp. stops decreasing—this is the tropopause which represents the upper boundary of the troposphere.

The Stratosphere Extends from the tropopause to nearly 50 km Almost all ozone is here In the lower area the temp. can be -60 C. In the upper area the temps. increase as the altitude increases-why?--the air is heated from above due to absorption of solar energy by the ozone. The stratopause is the upper area of the stratosphere.

Mesosphere Above the stratosphere Extends to about 80 km. Temps. will decrease with altitude increase—average temp. is -90C—coldest temperature in the atmosphere! Above this area the temperatures begin to rise again. Upper area is the mesopause

Thermosphere Above the mesosphere Temps. increase with altitude increase due to the nitrogen and oxygen molecules which absorb the solar radiation. Air molecules are very far apart here so accurate temp. readings are hard to get with accuracy. Lowest area is the ionosphere. (80-400 km).

In the ionosphere the atoms of gas lose electrons and produce ions and free electrons Interactions between the solar radiation and the ionosphere cause auroras.

Above the ionosphere is the exosphere This area extends for thousands of km.

Temperature Inversions This is the layering of warm air on top of cold air. This traps cool polluted air below.

The end of Section 22.1