Abstract
The complex chemistry and basic physics of Earth's atmosphere will be reduced to three main sections within the context of the chemical reactivities of predominant chemical species and the additional role of photochemistry from solar radiation. The three areas of chemical interactions and photochemical reactions in the atmosphere discussed are (1) the reactivities and relationships between chemical species that can affect tropospheric and stratospheric ozone concentrations, (2) reactions between chemical species that create acid rain, and (3) the chemical species, sources, and reactions that are believed to be contributing to climate change. These three areas in atmospheric dynamics will comprise this chapter along with some of the documented effects on ecological systems, human health, and infrastructure.
TopIntroduction
In 1994, physicist and astronomer, Carl Sagan, referred to the earth as a “pale blue dot” (Sagan, 1994, p. 7). His reference was from a National Aeronautics and Space Administration (NASA) photograph taken of Earth at his request by a receding Voyager 1 spacecraft as it approached the outer reaches of the solar system four billion miles from Earth. Earth appeared as one pale blue pixel in Saturn’s rings. Images of Earth taken from space all reveal a sapphire blue sphere surrounded by a gaseous envelope that is as essential for almost all lifeforms as liquid water. Earth’s atmosphere is a blanket of gases about 375 miles high, but about 99% of the gases and aerosols of the atmosphere are confined to the first 20 miles of altitude in regions of the atmosphere called the troposphere and stratosphere. The first studies of gases began with Boyle, Charles, Gay-Lussac, and Avogadro who each discovered fundamental relationships between gas properties of pressure, temperature, volume, and the quantity of gaseous atoms or molecules. With advances in atomic theory and chemistry by Dalton, Lavoisier, Priestly, and others, the birth of the new science of atmospheric chemistry occurred in the mid-18th and 19th centuries (Kotz, Treichel, Townsend, & Treichel, 2015).
Key Terms in this Chapter
Greenhouse Gases: Gases that can absorb in the infrared (heat) and prevent the transfer of heat back into space. The primary greenhouse gases are carbon dioxide, methane, nitrous oxide, and fluorinated gases.
Carbon Reservoirs: Places in which carbon is fixed and stored for various periods of time that can be later exchanged with carbon in other reservoirs. Forests, oceans, lakes, and soils are examples of carbon reservoirs. When the carbon is fixed and unable to leave the reservoir as in limestone or deep ocean sediments of planktonic calcites, it is in a carbon sink .
Photosynthesis: The process whereby plants remove CO 2 from the atmosphere and biosynthesize carbohydrates with sunlight as the energy source according to the reaction:
Acids: Chemical entities that can donate a hydrogen ion (H + ) which combines with a water molecule to form a hydronium ion, H 3 O + . As acidity increases, corrosivity also increases along with other harmful effects on lifeforms and ecosystems.
Free Radicals: Atoms or molecules that have one or more electrons occupying a half-filled electron orbital without a spin-paired electron. A powerful free radical in atmospheric chemistry is the hydroxyl radical that has one unpaired free electron.
Respiration: The process that returns CO 2 to the atmosphere. Animal life uses aerobic respiration with O 2 to obtain energy from carbohydrates, which releases CO 2 .
Carbon Cycle: The processes whereby carbon is converted to different forms of inorganic and organic compounds by biogeochemical processes and recycled from carbon stocks to carbon dioxide and then removed by capture into carbon reservoirs such as plant masses, soils, oceans, or carbon sinks (e.g., minerals).