Seminar: Science and the Atmosphere Freddie Arocho-Perez SC300: Big Ideas in Science

Atmosphere 7 miles 31 miles 50 miles 403 miles

Atmosphere

Radiation The atmosphere is the first line of defense against radiation from the Sun. Aurora Borealis: - The result of the emissions of light in the Earth’s upper atmosphere (ionosphere), above 80 km (50 miles), from nitrogen and oxygen atoms absorbing energy. - The absorption of energy comes from the collision of solar wind particles being funneled down and accelerated along the Earth’s magnetic field lines. - Oxygen: Green or Brownish-Red. - Nitrogen: Blue or Red.

Composition of the Atmosphere Because of the great variation in atmospheric conditions, the composition of gases in the atmosphere is not uniform. Lighter gases tend to rise to the top. Near the Earth’s surface, about 99% of the atmosphere is composed of nitrogen and oxygen.

Troposphere Although the troposphere is made up almost entirely of nitrogen and oxygen, other gases present in relatively small amounts still have a profound effect on the troposphere.

Ozone Ozone absorbs much of the radiation. It forms from reaction of molecular oxygen with the oxygen atoms produced in the upper atmosphere by photo-dissociation. O + O 2 --> O 3

Ozone Depletion In 1974 Rowland and Molina discovered that chlorine from chlorofluorocarbons (CFCs) may be depleting the supply of ozone in the upper atmosphere by reacting with it.

Chlorofluorocarbons CFCs were used for years as aerosol propellants and refrigerants. They are not water soluble (so they do not get washed out of the atmosphere by rain) and are quite unreactive (so they are not degraded naturally). The chlorine atoms formed react with ozone: Cl + O 3 --> ClO + O 2

Chlorofluorocarbons

In spite of the fact that the use of CFCs in now banned in over 100 countries, ozone depletion will continue for some time because of the tremendously unreactive nature of CFCs.

Water Vapor and Carbon Dioxide Gases in the atmosphere form an insulating blanket that causes the Earth’s thermal consistency.

Water Vapor and Carbon Dioxide This blanketing effect is known as the “greenhouse effect”. Water vapor, with its high specific heat, is a major factor in this moderating effect. But increasing levels of CO 2 in the atmosphere may be causing an unnatural increase in atmospheric temperatures.

Nitrogen Oxides What we recognize as smog, that brownish gas that hangs above large cities like Los Angeles, is primarily nitrogen dioxide, NO 2. It forms from car exhaust.

Photochemical Smog These nitrogen oxides are just some components of photochemical smog. Ozone, carbon monoxide, and hydrocarbons also contribute to air pollution that causes severe respiratory problems in many people.

Photochemical Smog As a result, government emission standards for automobile exhaust have become continually more stringent.

Sulfur Sulfur dioxide is a by-product of the burning of coal or oil. It reacts with moisture in the air to form sulfuric acid. It is primarily responsible for acid rain.

Sulfur High acidity in rainfall causes corrosion in building materials. Marble and limestone (calcium carbonate) react with the acid; structures made from them erode. This statue at the Field Museum in Chicago shows the effects of corrosion from acid rain and atmospheric pollutants (top). The same statue after restoration (bottom).