The Atmosphere

Atmospheric Pressure



Nitrogen is the most abundent gas
in our atmosphere at 78%



Oxygen is second at 20% - the
reason for this low amount because
oxygen readily interacts other
elements forming new compounds.



Why is oxygen is labeled as O

2

?

The reason is that two atoms of
oxygen are needed to make one
molecule of oxygen

.

Atmosphere Cont.



Ozone is very important in our
atmospehre



Ozone is labeled as O

3

It takes three

atoms to form one molecule of ozone



Ozone is important because it absorbs
harmful ultraviolet rays from the sun



Without the ozone layer humans would
be seriously burned by the sun’s
radiation.



Gases from aerosol spray cans and the
burning of hydrocarbons from aircraft
damage the ozone layer



Oxygen is always being added to
our atmosphere by the process of
photosynthesis.



The amount of oxygen produced
by plants from photosynthesis
each year equals the amount of
oxygen consumed by both plants
and animals. This is an equal
balance that has not changed for
hundreds of years.

Atmospheric Pressure



Gravity pulls the gases of the
atmosphere toward the Earth’s surface



Because of gravity - 99% off the total
mass of atmospheric gases is found
within 32 Km of the Earth’s surface



Atmospheric Pressure - is the ratio of
the weight of the air to the area of the
surface at which it presses against.

Atmospheric Pressure



Why do your ears pop at or during
a change in pressure?

The

popping sensation is due to the
decrease in air pressure on the
outside of your eardrum. When
the air pressure on both sides of
the eardrum is equal - the popping
stops.

Types of Barometers



Barometer - A devise that measures
atmospheric pressure



Mercurial Barometer - Uses a liquid -
mercury - The pressure squeezes mercury
up to a certain height inside a tube



Air pressure is measured of how high it
raises in the tube -

A reading of 760 mm on

this type of barometer is the Standard
Atmospheric Pressure at sea level

. This unit

is sometimes referred to as one atmosphere.



Standard Atmospheric Pressure is
referred to as 760 mm of mercury
or 29.92 inches of mercury

Barometers Continued



Official Weather Maps use
millibars One millibar is equal to
about 0.001 of standard
atmospheric pressure



Aneroid Barometer -

Aneroid means

without liquid -

This barometer is

mostly used today because it does
not contain mercury



Inside a aneroid barometer is a
sealed metal container with all the
air removed



When the atmospheric pressure
increases - the sides of the
container bend inward



When atmospheric pressure
decreases - the sides bulge out
again



Atmospheric pressure is marked by
a moving pointer on a scale



Aneroid barometers can also be
used to tell elevations above sea
level - This is called an Altimeter



The official SI units for air pressure
are called a pascal ( Pa )

Layers of the Atmosphere



Based on Temperature differences
scientists are able to identify four
layers of the atmosphere



They are

–

The Troposphere

–

The Stratosphere

–

The Mesophere

–

The Thermosphere

1. The Troposphere



Atmospheric layer closest to the
Earth’s surface



Troposphere comes from the Greek
word meaning change



All weather changes occur in the
troposphere - thus all water vapor
and carbon dioxide in the
atmosphere is found in this layer



Temperature decreases as the
altitude increases - at an average
rate of 6.5 degrees Celcius per
Kilometer

The Troposphere Cont.



At an average altitude of 10 Km the
temp. stops decreasing - this zone is
called the Tropopause



The Tropopause is the upper boundary
of the troposphere - its boundary
changes with latitude



For example at the equator it is found
to be 17 Km and at the poles it is 6 to 8
Km