Earth’s Atmosphere

Comic courtesy of Lab-initio.com

Layers of the Atmosphere

The troposphere contains approximately 80% of the atmosphere’s mass and 99% of its water vapor .

The stratosphere is actually increases in temperature as you move away from Earth. It also contains the ozone layer.

The mesosphere can be the coldest part of the atmosphere, where temperatures drop to 130 K (−226 °F; −143 °C). It is also where meteors disintegrate.

In the thermosphere temperatures can rise to 2,000 °C (3,630 °F). Radiation causes the atmosphere particles in this layer to become electrically charged enabling radio waves to bounce off and be received beyond the horizon. You would not feel warm in the thermosphere – there are too few atoms of gas to transfer significant heat. The International Space Station has a stable orbit within the middle of the thermosphere. Auroras occur in the thermosphere.

In the exosphere, beginning at 500 to 1,000 kilometers above the Earth's surface, the atmosphere turns into space.

Temperature and Pressure

in the atmosphere

Composition of the TroposphereGAS  Proportion

Nitrogen 78.0 %

Oxygen 21.0 %

Argon 0.9 %

Water Vapor 0.3-4.0 %

Carbon Dioxide 0.04 %

O3 (ozone) 10 ppmv

CH4 (methane) 1.6 ppmv

N2O (nitric oxide) 350 ppbv

CO (carbon monoxide)

70 ppbv

CFC’s 11-12 0.2-0.3 ppbv

Ozone Layer

Ozone, O3, is a colorless gas. Chemically, ozone is very active; it reacts readily with a great many other substances. Near the Earth’s surface, those reactions cause rubber to crack, hurt plant life, and damage people’s lung tissues. But ozone also absorbs harmful components of sunlight, known as “ultraviolet B”, or “UV-B”. High above the surface, above even the weather systems, a tenuous layer of ozone gas absorbs UV-B, protecting living things below.

Source: NASA Ozone Watch

The Ozone Cycle

Ozone DestructionSmall, mostly man-made organic molecules containing chlorine and/or bromine enter the atmosphere, and find their way to the stratosphere due to low reactivity.

CFCl3, Freon-11

Once in the stratosphere: CFCl3 + radiation → CFCl2 + Cl

The chlorine atom changes an ozone molecule to ordinary oxygen:

Cl + O3 → ClO + O2

The ClO from the previous reaction destroys a second ozone molecule and restores the chlorine atom, which can repeat the first reaction and continue to destroy ozone.

ClO + O3 → Cl + 2 O2

Sources of Stratospheric

Chlorine

Southern Hemisphere Ozone Hole

September 24, 2006

Source: NASA Ozone Watch

Each year for the past few decades during the Southern Hemisphere spring, chemical reactions involving chlorine and bromine cause ozone in the southern polar region to be destroyed rapidly and severely. This depleted region is known as the “ozone hole”.

Climate ChangeClimate change refers to any significant change in the measures of climate lasting for an extended period of time. In other words, climate change includes major changes in temperature, precipitation, or wind patterns, among other effects, that occur over several decades or longer.

Global warming refers to the recent and ongoing rise in global average temperature near Earth's surface. It is caused mostly by increasing concentrations of greenhouse gases in the atmosphere. Global warming is causing climate patterns to change. However, global warming itself represents only one aspect of climate change.

Source: U.S. EPA

Greenhouse GasesGases that trap heat in the atmosphere are called greenhouse gases. Each gas's effect on climate change depends on three main factors:

U.S. Greenhouse Gas Emissions in 2012

Total Emissions in 2012 = 6,526 Million Metric Tons of CO2 equivalentSource: U.S. EPA

How much of these gases are in the atmosphere?

How long do they stay in the atmosphere?

How strongly do they impact global temperatures? This is referred to as “Global Warming Potential, or GWP

Carbon DioxideCarbon dioxide, CO2, enters the atmosphere through burning fossil fuels (coal, natural gas and oil), solid waste, trees and wood products, and also as a result of certain chemical reactions (e.g., manufacture of cement). Carbon dioxide is removed from the atmosphere when it is absorbed by plants as part of the biological carbon cycle.

U.S. CO2 Emission Sources

Source: U.S. EPA100-year GWP = 1

Methane

Methane, CH4, is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from livestock and other agricultural practices and by the decay of organic waste in municipal solid waste landfills.

U.S. Methane Emission Sources

Source: U.S. EPA

100-year GWP = 21

Nitrous Oxide

Nitrous oxide, N2O, is emitted during agricultural and industrial activities, as well as during combustion of fossil fuels and solid waste.

U.S. N2O Emission Sources

Source: U.S. EPA

100-year GWP = 31 0

Fluorinated Gases

Hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride are synthetic, powerful greenhouse gases that are emitted from a variety of industrial processes. These gases are typically emitted in smaller quantities, but they are potent greenhouse gases.

U.S. Fluorinated Gas Emission Sources

Source: U.S. EPA

100-year GWP HFCs: 140-11,700 PFCs: 6,500-9,200 SF6: 23,900

Changes in Atmospheric Levels of Greenhouse Gases

Source: U.S. EPA

Ocean Acidity

Source: U.S. EPA

Ocean carbon dioxide levels have risen in response to increased carbon dioxide in the atmosphere, leading to an increase in acidity (that is, a decrease in pH).