17.1 The Atmosphere
Unit 7: Atmosphere, Weather, and
Climate
 Weather – the state of the atmosphere at
a given time
vs.
 Climate – weather over many years
Most important measurable
properties:
1. Temperature
2. Humidity
3. Type and amount of precipitation
4. Air pressure
5. Speed and direction of wind
Composition of atmosphere
 A mixture of gases:
– Nitrogen 78%
– Oxygen 21%
– Argon less than 1%
– CO2 less than 1%
– Water vapor varies from 1-4%
Volume of Clean, Dry Air
Variable Components / Human
Influence
 Water vapor is the source of all clouds &
precipitation. Water vapor absorbs heat
given off by Earth & some solar energy.
(Like CO2)
 Ozone (O3)
 Primary pollutants = emitted directly from
identifiable source
 Secondary pollutants = not emitted directly
into air.
Primary Pollutants
Structure of the Atmosphere
 Atmosphere rapidly thins
(pressure decreases) as
altitude increases (as
you travel away from
Earth)
 Atmospheric pressure is
the weight of the air
above
Layers of the atmosphere – based
on temperature changes
 Colder as you climb higher
 Divided into 4 layers based on temperature:
– Troposphere: bottom layer, temp decreases w/
increase in altitude
– Stratosphere: temp. remains constant to height ~20
km then gradually increases (heated…why?)
– Mesosphere: temps. decrease w/ height until
mesopause.
– Thermosphere: contains only tiny amt of the
atmosphere’s mass. Temps. Increase
Earth – Sun Relationship
 2 main motions
– Rotation: spinning on axis
– Revolution: movement of Earth in its orbit
around the sun
 Seasonal changes occur bc Earth’s position
to the sun constantly changes as it travels
along its orbit
 If the axis was NOT tilted we would not have
seasonal changes
 Axis points to the North Star
 Summer Solstice: 1st day of summer (NH
leaning toward the sun)
 Winter Solstice: 1st day of winter (NH leaning
away from the sun)
 Autumnal Equinox: Sept. 22 or 23 in NH
(occurs halfway btw the solstice)
 Spring Equinox: March 21 or 22 in NH (axis
neither leaning toward or away from the sun)
 Length of daylight = Earth’s position in orbit
– Summer = longer daylight
Review/Preview
1. List the layers and boundaries of
atmosphere in order from bottom to top.
2. What gas absorbs short wavelength UV
radiation? What gases absorb long
wavelength radiation?
3. Where are the answers to #2 found? (in
which two atmospheric layers?)