Unit 6: Composition and Structure of the Atmosphere A view from space showing the thin atmosphere hugging the Earth below the blackness of space.

OBJECTIVES Describe the constituents of the atmosphere and their relative concentrations Understand the origin of the atmosphere and how its composition has changed through time Discuss processes that add and remove important atmospheric gases and the resulting atmospheric residence times Survey the four temperature layers of the atmosphere together with their major properties

Contents of the Atmosphere Constant gases -found in the lower 100 km (homosphere). 99% of constant gases are nitrogen (78%) and oxygen (21%) Variable gases -includes the heterosphere, above 100 km where gases become lighter and less in abundance - carbon dioxide -water vapor -ozone Aerosols are mostly fine solid and liquid floating particles. Larger dust (> 1 micron) and aerosols (<1 micron) are found in abundance in urban regions and deserts. Aerosols play an important role in cloud formation, while also providing colors to the atmosphere through scattering.

Figure 2.19 Composition of the Homosphere

Huge amount of desert dust are lifted to great heights from an African desert and carried westward by winds aloft. Some will land in on U.S. beaches. Atmospheric particulates play important roles in cloud formation and in the energy budget of the Earth.

The scattering of sunlight by dust provides blue skies, white clouds and red sunsets. Source:

This colorful sunset is a result of scattering by dust transported high in the atmosphere. Here the deep red is caused by an Icelandic volcanic dust cloud. Aerosols Scatter Light Source: news/ iceland- volcano-eruptions-are- over-but-air-needs-time- to-clear news/ iceland- volcano-eruptions-are- over-but-air-needs-time- to-clear

Evolution of oxygen Amounts of oxygen from two different sources for the last 3 billion years or more.

Importance of Ozone Ozone filters out most of the UV radiation from the Sun Decreased concentration allows more of these harmful wavelengths to reach Earth’s surface – Increase risks of skin cancer – Impair the human immune system – Promote cataracts, clouding of the eye lens that reduces vision. May cause blindness if not treated Montreal Protocol was developed under the sponsorship of the UN to eliminate the production and use of CFCs

Antarctic Ozone Hole Figure FS 2.1.1

Mass of atmospheric CO 2 as a multiple of today’s value. Record of carbon dioxide levels compared to today’s amount for the last 600 million years.

The Hockey Stick Atmospheric CO 2 in the last 2000 years. Values before 1960 come from air trapped in glacial ice. The more recent record is based on air samples taken at a mountain observatory in Hawaii.

The Keeling Curve Carbon dioxide measurements taken at Mauna Loa, Hawaii since 1958.

Three forms of oxygen in the atmosphere Molecular oxygen (O2) Atomic oxygen (O) Ozone (O3) All 3 are vital for life on Earth

Column ozone distribution for October 15, 2011 in Dobson Units. Variable gases: ozone

Ozone levels in Dobson Units in April.

Variation of atmospheric temperature with height. The Layered Structure of the Atmosphere

The Northern Lights (Aurora Borealis) near Fairbanks, Alaska Source: