EARTH’S “OCEAN” OF AIR

Prepared by: Christelle Angelica C. Corpin

BSE- Biological Sciences

OUR ATMOSPHERE IS OUR LIFE

The Earth’s Atmosphere

• Earth’s atmosphere differs from those of other planets in the solar system.

• Venus – usually called “Morning Star” consist of 97% CO2 with dense clouds containing sulfuric acid.

• Jupiter and Neptune – consist of Hydrogen (H2), helium (He) and methane (CH4)

COMPOSITION OF AIR

• FACTS:a. Air is a mixture of many gases.b. The two most abundant gases in the air are nitrogen

and oxygen.c. The percentage by volume of gases in table 30 can

change as atmospheric conditions change.d. except for Carbon Dioxide, the gases in air are

chemical elements.e. Water vapor, although gaseous & commonly found in

the lower atmosphere, is not listed in table 30.

GAS SYMBOL % VOLUME (at sea level)

Nitrogen Ni 78. 30

Oxygen O2 20. 99

Argon Ar 0.94

Carbon dioxide CO2 0.03

Hydrogen H2 0.01

Neon Ne 0.00123

Helium He 0.0004

Krypton Kr 0.00005

Xenon Xe 0.0006

Radon Rn trace

Humidity – the amount of water vapor in the air that varies from 1- 4% by volume on the average. It is highest over bodies of water and under high atmospheric temperature when evaporation is rapid.

PROPERTIES OF MATTER

1. Air occupies space.2. Air consist of molecules of matter – tend to

spread out or diffuse throughout a vessel.- Air can be compressed where it concentrates

atmospheric gases near the ground.3. Air has mass – amount of matter in an object.4. Air has weight – Earth’s gravity pulls down on

the molecules of the gases in the air.

ATMOSPHERIC PRESSURE• Pressure – defined as force exerted on a

surface divided by its area.- The weight of the upper portion of the

atmosphere presses down, or compresses, the lower portion and all objects below it. This compression produces air pressure.

• Evangelista Toricelli – Italian mathematician discovered the weight of that column of air to be 14.69 pounds.

• He used a mercury barometer - an instrument that measures changes in atmospheric pressure, which he himself invented.

• The value 14.7 lb/in2 at sea level became known as one atmosphere (atm) = 1013. 25 newtons per square cm (N/cm2).

• Weathermen or meteorologists record atmospheric pressure using another unit of measurement called millibar (mb): 1 atm= 1013.25 mb or 103mb.

• Density – defined as mass per unit volume; atmospheric density is greatest at the bottom becoming less and less with altitude or more height.

• In the same manner, atmospheric pressure is greatest at the bottom.

• Atmospheric temperature – measure of the average kinetic energy (or energy of motion) of the molecules of an object (air mass) indicated by the rise and fall of the column of mercury in a thermometer.

• A higher temperature of air means that the molecules have greater kinetic energy. They are moving faster and bumping each other with greater force. Thereby throwing them apart.

• Warmer air is less dense than colder air; colder air is denser than warmer air.

MAJOR DIVISIONS OF THE ATMOSPHERE

Based on temperature variations

1. TROPOSPHERE

• Is the bottom 16 to 18 km of the atmosphere where winds, clouds and water vapor are found, and where weather phenomena occur.

• Temperature varies greatly near the earth’s surface. It is warmer near the equator and colder toward the poles.

• Air grows colder as one goes up higher. The temperature at the top of the troposphere is around -45*C to -50*C.

• The average depth of the troposphere is 11 km at the equator and 8 km at the poles.

2. STRATOSPHERE

• Second major division of the atmosphere; lies above the troposphere.

• It is in this region, the air grows warmer although not uniformly, as one goes up higher.

• 30 km deep; its outer boundary is around 50 km above sea level. 99.9% of the mass of the atmosphere is found within this 50 km of air.

3. MESOSPHERE

• 3rd major division of the atmosphere, above the stratosphere.

• Air grows colder again almost uniformly as one goes up higher . This is because gases in this region do not absorb the sun’s rays. The average rate of temperature decrease is about 3.5*C per km ascent.

• The average depth of the mesosphere is 30 km and its outer boundary is around 80 km above sea level.

BASED ON THE DISTRIBUTION OF GASES IN THE ATMOSPHERE

1. Homosphere – is the bottom 90 km of the atmosphere where there is continuous movement of air masses.

- N2 and O2 are well- mixed; comes from the prefix homo (meaning same), homogeneous mixture of gases in this region.

- A notable exception is the ozone layer that envelops the globe at around 30 km above sea level.

2. Heterosphere

• The outer portion of the atmosphere where no mixing of gases takes place.

- Gases tend to separate in layers; hetero meaning different.

BASED ON THE DISTRIBUTION OF OZONE & IONS

1. Ozonosphere – the bottom 70 km of the atmosphere where ozone is found.

Stratospheric Ozone – refers to the ozone in the ozone layer, some 30 km above sea level.

Ground level ozone – refers to the ozone formed near the earth’s surface, sometimes due to photochemical reactions involving air pollutants.

Ions – electrically charged particles; gas molecules in the upper atmosphere become ionized.

2. Ionosphere -the region of the atmosphere which is sufficiently ionized by solar ultraviolet radiation.

- This is the outer portion of the atmosphere where ions and electrons are trapped by Earth’s magnetic field and form layers referred to as D, E, F layers.

- They reflect radio waves back to the earth which plays an important role in radio transmission.