Earth’s Modern Atmosphere
Atmospheric Composition, Temperature,
and Function
Variable Atmospheric Components
Atmospheric
Profile
Atmosphere extends to
32,000 km (20,000mi)
from surface
Exosphere’s top is at 480
km (300 mi)
The atmosphere is
structured. Three criteria
to examine atmosphere
Composition
Temperature
Function
Atmospheric
Pressure
90% of atmosphere’s mass
is within 15 km of the
surface (the Troposphere)
Exosphere
Composition
Heterosphere
Homosphere
Atmospheric
Composition
Exosphere – outer
sphere
480 km (300 mi)
outwards as far as
32,000 km (20,000
mi)
Sparse field of
Hydrogen an
Helium atoms
loosely bound to the
earth by gravity.
Atmospheric
Composition
Heterosphere –
outer atmosphere
80 km (50 mi)
outwards to 480 km
Layers of gasses
sorted by gravity
H and He at outer
edge.
O and N at inner
edge.
<0.001% of mass of
atmosphere
Atmospheric
Composition
Homosphere –
inner atmosphere
Surface to 80 km
(50 mi)
Gasses evenly
blended
Homosphere
composition
Homosphere
composition
Why so much Nitrogen?
It is volatile in most
forms
Eg. Ammonia gas
It is unreactive with most
solid earth material
It is stable in sunlight.
Homosphere
composition
Why so much Oxygen?
Produced by
photosynthesis.
Homosphere
composition
Why so much Argon?
It slowly degasses from
rocks
It is unreactive so stays in
the atmosphere
Argon is a noble gas
Homosphere
composition
Why so little carbon
dioxide?
Original atmosphere was
probably about 25% CO2
It dissolves in water
It is used by plants in
photosynthesis
Exosphere
Heterosphere
Homosphere
Temperature:
Thermosphere
Thermosphere
The “heat sphere”
The top of the
thermosphere is the
thermopause (480km)
Roughly same as
heterosphere
80 km (50 mi) outwards
Swells and contracts
with the amount of
solar energy (250-550
km)
Temperature increases
rapidly with elevation
Temperature:
Mesosphere
Mesosphere
The mesopause is
the coldest part of
the atmosphere.
Middle
atmosphere
50 to 80 km (30 to
50 mi)
Temperature:
Stratosphere
Stratosphere
18-50 km (11-31
mi)
Temperature
increases with
altitude
Top is the
stratopause
Temperature:
Troposphere
Troposphere
Surface to 18 km (11
mi)
90% mass of
atmosphere
Normal lapse rate –
average cooling at rate
of 6.4°C/km
(3.5°F/1000 ft)
Environmental lapse
rate – actual local lapse
rate
Lapse Rate
Figure 3.5
Function:
Ionosphere
Ionosphere
Absorbs cosmic rays,
gamma rays, X-rays,
some UV rays
Atoms of become
positively charged
ions.
Charged ions of
oxygen an nitrogen
give off light to
generate the auroras.
Function:
Ozonosphere
Ozonosphere
Part of
stratosphere.
Ozone (O3)
absorbs UV
energy and
converts it to
heat energy.
Ozone hole
Ozone
concentration on
September 7th,
2003.
Formation of Ozone
Oxygen that we breathe (and plants
produce) is O2
UV radiation breaks down O2 into 2O.
O bonds with other O2 to give O3.
Ozone hole
Breakdown of ozone
CFC’s are broken down by strong ultraviolet radiation
to create chlorine atoms.
Cl acts as a catalyst to destroy O3 molecules.
Chlorine is not consumed by the reaction.
One Cl atom can destroy 100,000 O3 molecules.
Timescales
CFC’s take about 1 year to mix in with the troposphere
They take 2-5 years to mix in with the stratosphere
Why over Antarctica
Homogeneous versus Heterogeneous O3
depletion
Homogeneous depletion occurs over the
ozonosphere.
There has been a 5-10% drop in O3 levels over the
US.
Heterogeneous depletion occurs over Antarctica.
Atmospheric circulation over Antarctica is isolated
during the winter.
Cold temperatures encourage ozone depletion
Remedial action
Montreal Protocol (1987).
First global agreement to reduce atmospheric
pollution.
To phase out the use of CFC’s and other ozone
depleting chemicals.
Current status of the ozone hole.
Over the last 10 years the size of the ozone hole
has not increased as rapidly as it had in the past.
Atmospheric Pollution (in the
Troposphere)
Atmospheric pollution first
became a major problem with
the industrial revolution (in the
1800’s).
Coal burning created very dirty
air.
There are both natural and
anthropogenic sources for
pollution but most pollution
comes from humans.
Anthropogenic Pollution
Carbon monoxide
Photochemical smog
Industrial smog and sulfur oxides
Particulates
Anthropogenic Pollution Sources
Figure 3.10
Photochemical Smog
Natural Factors That Affect
Air Pollution
Winds
Local and regional landscapes
Temperature inversion
Temperature Inversion
Figure 3.9
Spatial scales of Pollution
The effects of pollution can be:
Global
Global Warming
Ozone hole
Regional
Acid rain
Local
Smog
Temperature inversions
The Clean Air Act
Enacted in 1963 and undated since then.
In response to massive smog conditions in
major cities.
Goals of the clean air act
The EPA sets permissible levels of
pollutants based on
Health effects
Environmental and property damage
90 million Americans live in areas that do
not meet these standards for at least one
pollutant.
Pollution Permits
All major stationary sources of pollution are
required to get permits that list all the pollutants
they emit.
Cap and Trade:
Recently programs have been enacted to allow factories
to trade these permits (only for specific pollutants).
There is an ultimate cap that total pollution from all
factories cannot exceed.
This allows the factories that can easily reduce
pollution to do so and then sell their permits to others.
New Source Review
Old power plants that produce lots of
pollution were “grandfathered” in under the
Clean Air Act so they produce much more
pollution than newer power plants.
New Source Review stipulates that these
older power plants are not allowed to
upgrade unless they use the new, less
pollution equipment.
Benefits of the Clean Air Act
Total direct costs = $523 billion
Estimated benefits = $5.6 to $49.4 trillion
– average $22.2 trillion
Net financial benefit $21.7 trillion
205,000 fewer deaths from 1970 to 1990!
How are these numbers calculated?