• 10-11 km (7 mi); 15-16 km at the equator; 5-6 km at the poles
• 75% of total mass
• Temperature generally decreases with height (Z)
• The "weather layer"

Stratosphere

• From 11 to 45-50 km
• Temperature is constant with height initially, then it increases with Z, known as an inversion (temp.increases w/z)
• 24% of total mass
• "Lid to the troposphere"
• Important to aircraft

Mesosphere (from the Greek "meso" meaning "middle")

• From 45 to 92 km
• Sharp decline in temperature -93°C (-137°F) at top

Thermosphere (from the Greek "thermo" meaning "heat")

• Increase in temperatures (extremely high due to absorption of radiation. Very few molecules.
• Topped by Exosphere
• Aurora Borealis and Aurora Australis

Other layers to classify the atmosphere

Ionosphere

• High in the thermosphere
• X-rays and ultraviolet rays ionize gases
• Radio waves depleted during the day

Ozonosphere

• From the bottom of the stratosphere to just above it
• Ozone absorbs ultraviolet radiation

Homosphere (homo means "same")

• Well-mixed gases from 0-80 km

Heterosphere (hetero means "different")

• Settling of gases according to weight above 80 km

Chemical Constituents of the Atmosphere

1. Nitrogen (N₂) - 78% (by volume)
2. Oxygen (O₂) - 21%
3. Argon (Ar) - 1%
4. Carbon Dioxide (CO₂) - 0.035% and rising!

Trace Elements (in varying amounts)

• H₂O (up to 4%)
• Sulfur Dioxide (SO₂)
• Nitrogen Dioxide (NO₂)
• Carbon Monoxide (CO)
• Ozone (O₃)
• Chlorofluorocarbons (CFC's)
• Methane (CH₄)
• Dust and other particulates
• Liquid water

Importance of Gases

Nitrogen - For all practical purposes it is inactive. We cannot use it directly. However, the "Nitrogen Cycle" says it can be broken down into usable compounds. Atmospheric nitrogen is converted into nitrogen compounds (nitrites and nitrates) by bacteria on plant roots (such as clover, soy bean and alfalfa) and by lightning from t-storms. It is then converted into protein (a usable form) where it is ingested by man and animals. Denitrification occurs when nitrogen is returned to the atmosphere by wastes and decomposition.

Oxygen - Discovered by Joseph Priestly in the late 1700's. Allows for breathing (respiration) and fire (combustion).

Argon - Inert. It is a noble gas.

CO₂ - Used in photosynthesis. It is a major pollutant resulting from the combustion of fossil fuels (which creates H₂O + CO₂). It is also known as a greenhouse gas because it absorbs Infrared (IR) radiation.

Ozone - Contained in the stratosphere (or called ozonosphere) absorbs ultraviolet radiation. Near the surface, ozone is a pollutant causing eye irritations, respiratory problems and dizziness. Ozone smells pungent and is the result of interactions of sunlight and car exhaust.

Chlorofluorocarbons (CFC's) act as catalyst to break down ozone. It is important in the stratosphere.

Methane - is another significant greenhouse gas. Methane is produced by decomposition and the expulsion of digestive gases.

Water- Besides its obvious importance, water is a greenhouse gas.


Dust (CCN) - Aerosols are airborne solids that can reflect incoming and outgoing radiation. Major sources include sea salt from evaporated sea spray, wind-blown dust and debris from volcanoes and fires, and from anthropogenic (man-made) sources. Particulates can remain suspended in the stratosphere for long periods of time and influence global weather, e.g. Krakatoa in 1883. Particulates can also act as cloud condensation nuclei CCN onto which water vapor condenses.

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