# The First Lecture of ATS 113 by Ejx7jD8z

VIEWS: 0 PAGES: 30

• pg 1
```									The First Lecture
of ATS 113
Jon M. Schrage
Overview of the Atmosphere:

• The atmosphere is very thin:

Earth : apple :: atmosphere : apple’s skin
Overview of the Atmosphere:

Actually, there is no “top”
to the atmosphere…
Overview of the Atmosphere:

Actually, there is no “top”
to the atmosphere…

• 90% is below 16 km (10 miles)
• 99% is below 50 km (30 miles)
• 99.999997% is below 100 km (60 miles)
“Air”
A mixture of gases and aerosols
“Air”
A mixture of gases and aerosols
Each gas has:
• sources – processes that add (“input”) the
gas into the atmosphere

• sinks – processes that remove (“output”)
the gas from the atmosphere
Each gas has:
• sources – processes that add (“input”) the
gas into the atmosphere
– For water vapor, this would be
EVAPORATION.
• sinks – processes that remove (“output”)
the gas from the atmosphere
– For water vapor, this would be
CONDENSATION.
Each gas has a:
• reservoir – the amount of the gas currently
being held in to the atmosphere

• residence time – how long a typical
molecule of the gas is going to be in the
atmosphere before being removed by a
sink
reservoir
residence time 
input rate
reservoir
residence time 
input rate
• Consider the case of water vapor:
– The “reservoir” of water vapor is relatively
small (compared to other gases).
– However, the input rate is very, very fast—
there is lots of evaporation.
– Therefore, the residence time is pretty short—
reservoir
residence time 
input rate
• Consider the case of oxygen:
– The “reservoir” of water vapor is relatively
large (compared to other gases).
– The input rate is fairly fast (photosynthesis in
plants).
– Therefore, the residence time is pretty
reservoir
residence time 
input rate
• Consider the case of nitrogen:
– The “reservoir” of nitrogen is huge (compared
to other gases).
– However, the input rate is very, very slow—
there is almost no production of N2.
– Therefore, the residence time is very long—
“Residence time” is important…
…because it helps explain the difference
between two types of gases in the
atmosphere:
concentration at every
location in the atmosphere.
1. Constant (“permanent”) constituents
2. Variable constituents

Occur at a range of concentrations at
different locations in the atmosphere.
Constant (“Permanent”)
Constituents
• Their concentration is in “steady state”.
• Their sources and sinks are in some kind
of “equilibrium”.
Constant (“Permanent”)
Constituents
•   Nitrogen 78%
•   Oxygen 21%
•   Argon .9%
•   Neon .0018%

Nitrogen   Oxygen   Argon   Neon
Variable Constituents
•   Water Vapor 0-4% (averages about 0.25%)
•   Carbon Dioxide (averages about 0.038%)
Variability of Water Vapor
Variable Constituents
•   Water Vapor 0-4% (averages about 0.25%)
•   Carbon Dioxide (averages about 0.038%)
Variability of Carbon Dioxide

• Trend (due to the burning of fossil fuels)
• Annual Cycle (due to the fact that there are more
plants in the Northern Hemisphere than the
Southern Hemisphere)
Variable Constituents
•   Water Vapor 0-4% (averages about 0.25%)
•   Carbon Dioxide (averages about 0.038%)
Variability of Ozone
Variable Constituents
•   Water Vapor 0-4% (averages about 0.25%)
•   Carbon Dioxide (averages about 0.038%)
Variability of Methane

• Sources of methane: cattle flatulence, termites,
Aerosols
Aerosols
• The atmosphere also contains
“aerosols”— suspended solid and liquid
particles (other than water and ice).
• Soot, smoke, dust, salt, pollen…
Origin of the
Atmosphere
First
Atmosphere:
billion years ago.
Mostly hydrogen
and helium.
We lost this
atmosphere.
Second
Atmosphere:
Formed by volcanic
outgassing.
Nitrogen, carbon
dioxide, water
vapor…
Oxygen
Oxygen

• Does not occur due to volcanic
outgassing.
• Byproduct of photosynthesis.
• Concentrations rose (from zero) once life
evolved.

```
To top