Composition and Layers of the Atmosphere

Mr. Silva

Ag Earth Science

Composition of the Atmosphere• Nitrogen 78.08%• Oxygen 20.95%• Argon 0.93% (9300 ppm)• Carbon Dioxide 0.035% (350 ppm)• Neon 18 ppm• Helium 5.2 ppm• Methane 1.4 ppm• Ozone 0.07 ppm

3. Composition of the Atmosphere

Other Components of the Atmosphere

• Water Droplets• Ice Crystals• Sulfuric Acid Aerosols• Volcanic Ash• Windblown Dust• Sea Salt• Human Pollutants

3. Composition of the Atmosphere

Aerosols

Aerosols Any solid or liquid particle in the

atmosphere.

• Natural (e.g. dust) and human (e.g. soot) sources.

• Can remain suspended for long periods of time (days to weeks).

• Contribute to cloud formation and precipitation by acting as condensation nuclei.

Aerosols: Saharan Dust Storm

Dust particles are about 10 micro-meters in size (0.00001 meters). Roughly 1/10 the

width of a human hair. Big ones settle out..

Aerosols: Pollution over Los Angeles

Ozone: O3

Partial PressureGas Molecular

WeightPartial

Pressure

Nitrogen 28 78%

Oxygen 32 21%

Argon 40 0.9%

Water Vapor 18 0-4%

Carbon Dioxide 44 350 ppm

2. Partial pressure, vapor pressure and humidity

Layers of the Atmosphere

Structure (Layers) of the Atmosphere

• Defined by Temperature Profiles• Troposphere

– Where Weather Happens

• Stratosphere– Ozone Layer

• Mesosphere• Thermosphere

– Ionosphere

4. Layers in the atmosphere are defined by temperature profiles

The Troposphere

• Most dense• All weather takes place here

Troposphere• Heating of the Surface creates warm air at

surface• Warm air rises, but air expands as it rises

and cools as it expands (Adiabatic cooling)

• Heating + Adiabatic Cooling = Warm air at surface, cooler air above

• Buoyancy = Cool air at surface, warmer air above

• Two opposing tendencies = constant turnover4. Layers in the atmosphere are defined by temperature profiles

The Stratosphere

• Dry• Absorbs ultraviolet

radiation (UV)• Ozone layer is here

• Ozone (O3) absorbs much UV C and UV B waves.  

Stratosphere

• Altitude 11-50 km• Temperature increases with altitude• -60 C at base to 0 C at top• Reason: absorption of solar energy to

make ozone at upper levels (ozone layer)

• Ozone (O3) is effective at absorbing solar ultraviolet radiation

4. Layers in the atmosphere are defined by temperature profiles

The Mesosphere

• Coldest• Many meteors burn up here

Mesosphere

• 50 – 80 km altitude• Temperature decreases with altitude• 0 C at base, -95 C at top• Top is coldest region of atmosphere

4. Layers in the atmosphere are defined by temperature profiles

The Thermosphere (Ionosphere)

• Region of charged ions (positive) and electrons

• Electrons are torn off atoms by sunlight of short wavelengths

• Electrons don’t recombine easily because the distance between molecules is large at high altitudes and collisions are not frequent

Thermosphere

• 80 km and above• Temperature increases with altitude as

atoms accelerated by solar radiation• -95 C at base to 100 C at 120 km• Heat content negligible• Traces of atmosphere to 1000 km• Formerly called Ionosphere

4. Layers in the atmosphere are defined by temperature profiles