The Atmosphere

StructureStructure

CompositionComposition

EvolutionEvolution

Gas Laws (T and P)

Moisture

Anthes chapters 1 and 2

Structure

Source: Anthes 1.4

Structure

LAYER A (km) P (atm) T (oC) COMMENTS

Exosphere 500+ 0 103+ Edge of space, light gases escape

Thermosphere 90+ 10-7 -90 to103 Stable, Solar absorption by O & O2

Mesosphere 60-90 10-5 0 to -90 Mixed layer, coldest region

Stratosphere 20-50 10-2 -40 to 0 Stable, Solar UV absorbed by O3

Troposphere 0-10 1 to 0.1 40 to-40 Layer of weather, water vapor rules

Composition

Nitrogen 78.08%

Oxygen 20.95%

Water Vapor 0 to 4%

Argon 0.93%

CO2 0.0387% = 387 ppm

The Minor ConstituentsConstituent Symbol ppmNeon Ne 18.0Helium He 5.2Methane (v) CH4 1.7Krypton Kr 1.1Sulphur Oxides (v) SOx 1.0Hydrogen H2 0.5Nitrous Oxides (v) NOx 0.3Carbon Monoxide (v) CO 0.2Xenon Xe 0.09Ozone (v) O3 0.04Particulates (v) 0.01CFCs (v) CFCs 1x10-4

Radon (v) Rn 6x10-14

Note: Every known chemical compound has been found in the atmosphere in some concentration (e.g. paint fumes, lead compounds, CCl4, etc.)

Note: Every known chemical compound has been found in the atmosphere in some concentration (e.g. paint fumes, lead compounds, CCl4, etc.)

Hart’s Model of Evolution of Atmosphere

M.H. Hart, Icarus 33 (1978): 23−39.

Evolution of the Atmosphere

1. ASTRONOMICAL ATMOSPHERE

Formation of the solar system 4.6 x 109 yrs. ago.Heavier elements produced in supernovas.Early cold Earth had an atmosphere of H2, He,

CH4, NH3 and water vapor (from bombardment by comets). This early atmosphere is thought to be much like those of the Jovian planets.

Sun retained H and He and became a fusion reactor with high T and P in its core.

When Sun ignited, Earth heated and was too close to retain H and He which were lost to space.

Evolution of the Atmosphere

2. GEOLOGICAL ATMOSPHERE

Outgassing by volcanoes and other fissures enriched the Earth’s atmosphere in H2O and CO2.

Some volcanoes emit about 80% water vapor and about 12% carbon dioxide.

Thus, after the Earth solidified, the atmosphere was largely composed of these compounds.

Comets continued to bombard the early Earth providing water and other atmospheric gases.

Evolution of the Atmosphere3. BIOLOGICAL ATMOSPHERE

Very little oxygen until plant life evolved.

If all plant life was extinguished, we would run out of oxygen in as little as 40 years!

1% of the O2 may have come from lightning strikes or UV solar radiation:

2 H2O + energy --> 2 H2 + O2

99% came from the growth of plants:

6 CO2 + 6 H2O + energy --> C6H12O6 + 6 O2

Carbon dioxide + water + sunlight --> Organic material + Oxygen

Evolution of the Atmosphere

4. SOCIO-ECONOMIC ATMOSPHERE

Since the Industrial Revolution, the atmosphere has changed drastically from its earlier forms. Humans have changed its composition through pollution of all kinds (smoke, smog, acids).

Our use of fossil fuels has led to the following one way and unsustainable equation:

C6H12O6 + 6 O2 --> 6 CO2 + 6 H2O + energy

Organic material + Oxygen --> Carbon dioxide + water + energy

Anthropogenic ParadoxWill Homo sapiens, through overpopulation, resource

depletion, and misuse of technology upset the natural rhythms of organic life on our planet?

The Anthropogenic Paradox implies the unintended possible self-destruction of Homo sapiens sapiens, the first species to be fully aware of its own extinction.

The Anthropocene is the term used for the current and recent era in which humans are influencing global processes. When did this begin? 1990? 1790? early agriculture? Could it be called the Anthro-obscene?

DefinitionsWeather The state of the atmosphere at a given place and time.

Weather elements: T, P, humidity, clouds, precipitation, visibility, wind, air quality.

Meteorology Scientific study of the weather.

Ancient meaning (Aristotle) was much broader.

Climate Aggregate of regional weather conditions over time.

Usually a 30-year average over a region plus

A statement about frequency of extreme conditions,

such as lightning strikes, tornadoes, or drought.

Climatology Scientific study of climate.

Includes fields such as applied climatology, climate

modeling, and climate dynamics.

Definitions (cont.)

Physical Oceanography -- Chemistry and dynamics of oceans, including currents, waves, air-sea interaction, and topics such as El Niño and La Niña.

Atmospheric Science -- Umbrella term covering explosion of research specialties since about 1960. Meteorology, Climatology, Cloud Physics, Atmospheric Chemistry, Numerical Weather Prediction, Satellite and Radar Meteorology, etc.

Global Change or Earth system science -- Umbrella term for study of the complex interactions of the atmosphere, lithosphere, hydrosphere, and biosphere on all temporal and spatial scales plus the human or social dimensions of environmental change.

Weather Elements

Air Temperature Thermometer

Air Pressure Barometer

Humidity Psychrometer

Clouds Cloud types and amounts

Precipitation Liquid or Frozen

Wind Speed and Direction

Visibility For Aviation

Air Quality Pollution Load

The Gas LawsThe Gas Laws

Temperature (T)

Measure of the kinetic energy of the molecules.

Average speed of an air molecule at room T ??

= 450 m/sec = 1000 mph !

Heating speeding up molecules

Cooling slowing down molecules

Absolute zero (0 K) = No thermal motion

Temperature scales

Kelvin (K) Centigrade (C) Fahrenheit (F)

Boiling 373 100 212

Freezing 273 0 32

Ab. Zero 0 -273 -459

Temperature conversionsK = C +273 for example 0 C = 273 KC = 5/9 (F-32) for example 70 F = 21 C; 32 F = 0 CF = 9/5 C + 32 for example 0 C = 32 F; 40 C = 104 F

http://www.eskimo.com/~jet/javascript/convert.html

Charles’ Law

V = c2 T (at constant pressure)

V is proportional to T.

V1/V2 = T1/T2

Example: 2 litres/ 3 liters = 200 K/ 300 K

Pressure -- PPressure is defined as force/unit area.

It is the force exerted by the weight of the atmosphere.1 atmosphere = 1013 mb = 14.7 lbs./in.2

How much force does the atmosphere exert on your body?1000 in.2 x 14.7 lbs./in.2 = 14,700 lbs. = over 7 tons of force!

Air molecules at sea level collide 109 times per second.Air pressure decreases with height (faster in cold air).

29.92 in. of mercury = 34 feet of water1 atmosphere = 1013.25 millibars (mb) = 1013.25 hPascals

This is standard sea level pressure

Torricellian Experiment (1644)Nature does not “abhor a vacuum” and the air has weight.

Magdeburg Hemispheres (1657)

In Germany Otto von Guericke constructed an air pump which he used to evacuate two large sealed hemispheres. The weight of the air pushing the hemispheres together was so great that 16 horses were needed to pull them apart.

An experiment on a bird in the air pump, by Joseph Wright

Density -- = mass/volume [kg/m3]

Dry air is slightly denser than moist air at the same T and P

Boyle’s Law

PV = constant

P1V1 = P2V2

Example: 1 atm. x 1 liter = 0.5 atm. x 2 liters

In the atmosphere, use density instead of volume.

P = c1 (at constant temperature)

Ideal Gas Law

P = RT

Where P is pressure, is density, R is the gas constant, and T is temperature in degrees Kelvin.

At the same pressure, cold air is denser than warm air.

Dalton’s Law of Partial Pressures

The total pressure of the air is the sum of the partial pressures of its component gases.

Ptotal = PN2 + PO2 + e + Ptrace

Total = Nitrogen + Oxygen + Water Vapor + Trace Gases