22.1 Characteristics of the Atmosphere

Characteristics of the Atmosphere

Section 22.1

Atmosphere· layer of gases that surrounds the Earth· air = mixture of chemical elements and compounds in the atmosphere· functions (2)

protect Earth's surface from the sun's radiationhelp regulate Earth's surface temperature

Composition of Atmosphere· gases

nitrogen - 78%, oxygen - 21%, argon, CO2, and other - 1%· water vapor

enters by evaporation from oceans, fresh water, and plants

most near surfacedecreases with height

· ozone - O3

form of oxygen gasabsorbs harmful ultraviolet radiation from the sunless ozone = more UV rays reach Earth's surface = sunburn

and cancerthinning results from chlorofluorocarbons (CFCs) which

breaks down ozone· particulates

dust, ash, pollen, bacteria, salthelps form fog & rain (water clings to particulates)tiny particles can stay in the air for months or years

Atmospheric Pressure· pressure exerted on Earth's surface by the atmosphere· decreases as altitude increases

gravity not as strong at high altitude, so air molecules move further apart and exert less pressure· decreases as temperature increases

molecules move further apart as air heats up· decreases as water vapor increases

water vapor is less dense (or lighter) than oxygen and nitrogen molecules

Measuring Atmospheric Pressure· tool = barometer· units = atmosphere (atm), millimeters of mercury (mm Hg), and millibars (mb)· standard atmospheric pressure at sea level = 1 atm = 760 mm Hg = 1000 mb

Layers of Atmosphere· 4 layers based on temperature· troposphere = 0 - 12 km· stratosphere = 12 - 50 km

contains ozone layer· mesosphere = 50 - 80 km· thermosphere

ionosphere = 80 - 400 kmexosphere = 400 - ? km

22.1 Characteristics of the Atmosphere

Troposphere· closest to Earth's surface· weather occurs here· contains gases essential to life· temperature decreases with altitude

heated by thermal energy that comes from Earth's surface· average altitude = 12 km

depends on latitude and season

Stratosphere & MesosphereSTRATOSPHERE

· strong winds and few weather changes· contains ozone· temperature increases with altitude

heated by absorption of solar energy by ozone

MESOSPHERE

· temperature decreases with altitude· coldest temperatures in atmosphere

Thermosphere· temperature increases with altitude

nitrogen and oxygen absorb solar energyas high as 1000 C

· ionosphere = lower portionions formed when UV rays from sun knock electrons

off oxygen atoms· exosphere = upper limit of indefinite altitude