Earth’s Modern AtmosphereAtmospheric 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

CompositionTemperatureFunction

Atmospheric Pressure

90% of atmosphere’s mass is within 15 km of the surface (the Troposphere)

CompositionHeterosphere

Homosphere

Exosphere

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 kmLayers of gasses sorted by gravityH 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

Heterosphere

Homosphere

Exosphere

Temperature: Thermosphere

ThermosphereThe “heat sphere”The top of the thermosphere is the thermopause (480km)Roughly same as heterosphere80 km (50 mi) outwardsSwells and contracts with the amount of solar energy (250-550 km)Temperature increases rapidly with elevation

Temperature: Mesosphere

MesosphereThe mesopause is the coldest part of the atmosphere.

Middle atmosphere

50 to 80 km (30 to 50 mi)

Temperature: Stratosphere

Stratosphere18-50 km (11-31 mi)

Temperature increases with altitude

Top is the stratopause

Temperature: Troposphere

TroposphereSurface to 18 km (11 mi)90% mass of atmosphereNormal 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:IonosphereIonosphere

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 OzoneOxygen that we breathe (and plants produce) is O2

UV radiation breaks down O2 into 2O.

O bonds with other O2 to give O3.

Ozone holeBreakdown 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.

TimescalesCFC’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 actionMontreal 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 WarmingOzone hole

RegionalAcid rain

LocalSmogTemperature 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 actThe 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 PermitsAll 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 ReviewOld 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 ActTotal 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?