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 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 The mesopause is the coldest part of the atmosphere. Middle atmosphere 50 to 80 km (30 to 50 mi)

Temperature: Stratosphere 18-50 km (11-31 mi) Temperature increases with altitude Top is the stratopause

Temperature: 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 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 Timescales 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?