Download 915 Lecture, Stucture, Composition, Evolution, Laws

The Atmosphere
Structure
Composition
Evolution
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
Oxygen
Water Vapor
Argon
CO2
78.08%
20.95%
0 to 4%
0.93%
0.0387% = 387 ppm
The Minor Constituents
Constituent
Neon
Helium
Methane (v)
Krypton
Sulphur Oxides (v)
Hydrogen
Nitrous Oxides (v)
Carbon Monoxide (v)
Xenon
Ozone (v)
Particulates (v)
CFCs (v)
Radon (v)
Symbol
Ne
He
CH4
Kr
SOx
H2
NOx
CO
Xe
O3
CFCs
Rn
ppm
18.0
5.2
1.7
1.1
1.0
0.5
0.3
0.2
0.09
0.04
0.01
1x10-4
6x10-14
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 Atmosphere
3. 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 Paradox
Will 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 Anthroobscene?
Definitions
Weather
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
Air Pressure
Humidity
Clouds
Precipitation
Wind
Visibility
Air Quality
Thermometer
Barometer
Psychrometer
Cloud types and amounts
Liquid or Frozen
Speed and Direction
For Aviation
Pollution Load
The 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
Boiling
Kelvin (K)
Centigrade (C)
Fahrenheit (F)
373
100
212
Freezing
273
0
32
Ab. Zero
0
-273
-459
Temperature conversions
K = C +273
for example
C = 5/9 (F-32)
for example
F = 9/5 C + 32
for example
0 C = 273 K
70 F = 21 C; 32 F = 0 C
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 -- P
Pressure 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 water
1 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