Planetary Atmospheres, the Environment and Life (ExCos2Y) Topic 1: Composition of Atmospheres Chris...
-
Upload
alice-crawford -
Category
Documents
-
view
221 -
download
0
Transcript of Planetary Atmospheres, the Environment and Life (ExCos2Y) Topic 1: Composition of Atmospheres Chris...
Planetary Atmospheres, the Environment and Life (ExCos2Y)
Topic 1: Composition of Atmospheres
Chris Parkes [email protected]
Rm 455 Kelvin Building
Lecture Content
• 1. Composition of the Atmospheres of Earth, Mars and Venus
• 2. Evolution of Earth’s Atmosphere
• 3. Structure of Planetary Atmospheres
• 4. Solar Radiation
• 5. Atmospheric Convection
• 6. Wind
• 7. Water
• 8. Storm Systems
• 9. Climate Change
• 10. RevisionReading: The Cosmic Perspective, chapter on planetary atmospheresby Bennett, Donahue, Schneider, Voit. Publisher: Addison Wesley Atmosphere, Weather and Climate by Barry, Chorley. Publisher: Routledge
Planets of the solar system
• Orbit the Sun
• Near Spherical
• Dominate its orbit IAU Prague (2006)
Fit to be a planet ?
Atmospheric Composition:
Earth, Mars & Venus
Earth MarsVenus
Earth MarsVenus
Atmospheric Composition:
Earth, Mars & Venus
Comparison of physical quantities:
Earth MarsVenus Earth MarsVenus
Mass * 0.82 1.00 0.11
Distance from Sun * 0.72 1.00 1.52
Radius * 0.95 1.00 0.53
Gravitational Acc. * 0.90 1.00 0.38
Surface Pressure (atm.) 90.00 1.00 0.01
Surface Temp. (K) 750. 280. 240.
Planetary Albedo 0.76 0.39 0.16
Rotation Period (days) 243. 1.00 1.03
Orbital period (years) 0.62 1.00 1.88* Relative to Earth
Comparison of Atmospheric Composition
Earth MarsVenus
Nitrogen 3.5% 78% 2.7%
Oxygen <0.001% 21% 0.13%
Carbon Dioxide 96.5% 0.035% 95.3%
Argon 0.007% 0.93% 1.6%
Water Vapour 0.004% .004%-4.0% 0.03%
Equilibrium state: production rate = loss rate
• Sources & Sinks (in balance)• Sensitive dependant on: temperature, pressure, quantity, other gases, etc.
Partial Pressures
Partial pressure of a gas = P total atmospheric × % concentration
Examples:
N2 on Venus: 3.5% × 90 = 3.15 atm.
N2 on Earth:
CO2 on Mars:
CO2 on Earth:
78% ×1 =
95.3% × 0.01 =
0.035% × 1 =
0.78 atm.
0.00953 atm.
0.00035 atm.
Some Important Gases
• CO2 – Greenhouse gas: temperature– Needed for photosynthesis: life
• H2O– Sink for CO2
– Liquid Water needed for life on earth
• Oxygen• O2
– needed for life on earth
• O3 (Ozone)– Pollutants through human activities (Low atmosphere)– Formed by Sun’s radiation (High atmosphere)– UV screen
How does a planet GAIN atmospheric gases ?
Born 4.5 million years ago without atmospheres
• Outgassing– Heating from the core– Volcanic activities
– H2O, CO2, N2, H2,S, SO2
• Evaporation/sublimationWater (Earth) /ice (Earth, Mars) and frozen CO2 (Mars)
How does a planet LOSE atmospheric gases ?
Five processes:1) Condensation2) Chemical Reactions
3) Thermal Escape4) Impacts5) Dissociation from solar rays
These two can be reversed These three permanent loss
The presence of water
affects CO2 levels
- CO2 highly soluble in water- Acid rain which reacts with rock
- CO2 locked into rocks(over geological timescale)
1. Removal of CO2 from atmosphere(see next lecture for Oxygen cycle)
Chemical Reactions
Thermal Escape: Gravity and the atmosphere
Escape velocity (Ve):
G – Gravi. Const.
(6.67×10-11m3s-2kg-1)
M – Mass of Planet
r - Planet radius
For Earth Ve = 11km/s
r
GMve
2
Gravity and the atmosphere
Motion of Gas molecules:
- random
- temperature dependant velocity
No.
of
mol
ecu
les
Velocity
R – gas constant
(8.31 J mol-1 K-1)
T – temperature
m – molecular weight
(=0.002kg/mol for H2)
At 280K, Vmax = 1.5km/sVe
m
RTvrms
3
Temperature & escape velocity of planet are determining factors of atmospheric composition
- Points show vescape and temperature of each planets
- Curves show typical highest velocities for different gases
Temperature (K)
Thermal Escape
Vescape(km/s)
Earth’s atmosphere – other constituents
• Aerosols– Types: Dust, Organic matter, Smoke, Salt
– Sources: Forest/Bush Fire, Volcano, Sea Spray, Dust Storm, Burning fossil Fuel
• Pollutants– Sulphur compounds (acid rain), Nitrogen compounds
(NOx), Ozone, CO, Hydrocarbons
• Water vapour– Cloud formation
Earth’s atmosphere – Cloud formation
Planetary Albedo
Water vapour saturation
Temperature
Pressure
aerosols
Highly reflective( 70%-95% Visible range)
Efficient scatterer
Many different
types of cloud
Example exam questions
Q1. List the main differences between atmospheric composition of Mars and Earth?
Q2. What are the main factors which affect surface temperature of planets?
Q3. How does surface temperature affect the composition of planetary atmosphere?
Next lecture – evolution of Earth’s atmosphere