Teacher Fact Sheet

Air...we know it’s there. It envelops the earth and makes life possible. Our lungs need about 35 pounds of it everyday. The atmosphere — air — is made up mostly of nitrogen (about 78%) and oxygen (21%) with a few other gases. It also has some water vapor and small particles called aerosols. The atmosphere extends 50 km (31 mi) from the surface of the Earth. Air in the atmosphere is a mixture of gases not physically uniform, but consists of layers that vary in relation to temperature, pressure, and altitude. The boundaries between these four layers are defined by abrupt changes in temperature. The biosphere, which is the part of the Earth where all life resides, is surrounded by four atmospheric layers. They are the troposphere, stratosphere, mesosphere, and thermosphere. The two layers we will be concentrating on are the troposphere and the stratosphere.

The troposphere, only 10 km (6 mi) is the closest and warmest layer to Earth’s surface. The troposphere cools as it gets higher, and it is here where clouds and weather occur.

Above the troposphere is the stratosphere which extends 50 km (31 mi) above the Earth. This is where ozone, a form of oxygen that absorbs much of the harmful radiation from the sun, is formed.

Driving Earth’s weather is the sun. The sun sends out different waves of energy, most of it as visible light, which can be detected by the eyes. Other waves of the sun’s energy are invisible and include infrared light, which can be felt as heat, and ultraviolet light, which is blocked by the upper atmosphere.

But the sun does not heat the Earth very much. Solar radiation passes through the atmosphere, and the Earth absorbs much of it and reflects some of it back into space. Particles in the atmosphere also bounce radiation back into space. Greenhouse gases such as carbon dioxide and water vapor absorb the sun’s energy and warm the atmosphere. They act as an insulating layer trapping heat in the atmosphere then return this warmth back to the Earth, causing the surface to warm up more and put more heat back into the atmosphere. This feedback system is called the greenhouse effect, and without it, the Earth would be lifeless. Living organisms and water keep the atmosphere from heating up too much. Carbon dioxide is stored in oceans, and plants use carbon dioxide to make food during photosynthesis.

All of the heating and cooling that occurs between the Earth’s surface and atmosphere is important in keeping the air circulating around the globe. As the air circulates, it carries heat and water vapor from place to place. All of this movement results in the weather, the local conditions at one time and place. Daily weather includes precipitation (rain, sleet, snow), clouds, and temperature. Climate is the general weather of an area over a long time. For example, the overall climate of Portland, Oregon, is cooler and wetter than the general climate in Tulsa, Oklahoma.

Both climate and weather depend on the water cycle. Water evaporates from oceans, lakes, and rivers into the atmosphere. The atmosphere carries the water vapor to other places, where it eventually forms clouds and finally falls as precipitation.

Other things affect weather and climate. The farther from the equator or the higher in the air a place is located means cooler temperatures. Oceans keep a place from getting

too hot or too cold. Land features such as mountains affect climate and weather by changing the way the wind blows and the amount of rainfall. Even large cities affect the weather. Because there are more buildings and fewer trees and grass, a large city is warmer than the rural area surrounding it. This is called an Urban Heat Island. This alters the air circulation over the cities and the areas downwind from them.

The air we breathe in many U.S. cities is being polluted by activities such as driving cars and trucks; burning coal, oil, and other fossil fuels; and manufacturing chemicals. Air pollution can even come from smaller everyday activities such as dry cleaning, mowing the lawn, filling your car with gas, and degreasing and painting operations. These activities add pollution to the air we breathe. When these pollutants accumulate in the air in large enough amounts, they may harm us and our environment. More people in cities and surrounding counties means more cars, trucks, industrial and commercial operations, and generally means more pollution.

Air pollution is a problem for all of us. The average adult breathes over 3,000 gallons of air every day. Children breathe even more air per pound of body weight and are more susceptible to air pollution. Many air pollutants, such as those that form smog and toxic compounds, remain in the environment for long periods of time and are carried by the winds hundreds of miles from their origin. Millions of people live in areas where smog, very small particles, and toxic pollutants pose serious health concerns. People exposed to high enough levels of certain air pollutants may experience burning in their eyes, an irritated throat, or breathing difficulties. Long-term exposure to air pollution can cause cancer and long-term damage to the immune, neurological, reproductive, and respiratory systems. In extreme cases, it can even cause death.