| A | B |
|---|
| WEATHER | The conditions of Earth's atmosphere at a particular time and place. |
| ATMOSPHERE | The mixture of gases that surrounds Earth. The outermost of the four spheres into which scientists divide Earth. |
| OZONE | A form of oxygen that has three oxygen atoms in each molecule instead of the usual two. |
| WATER VAPOR | The invisible, gaseous form of water. |
| POLLUTANT | Harmful substance in the air, water, or soil. |
| PHOTOCHEMICAL SMOG | A brownish haze that is a mixture of ozone and other chemicals, formed when nitrogen oxide, hydrocarbons, and other pollutants react with one another in the presence of sunlight. |
| TEMPERATURE INVERSION | A layer of warm air prevents a layer of cooler air below it from rising. |
| ACID RAIN | Rain that is more acidic than normal, caused by the release of molecules of sulfur dioxide and nitrogen oxide into the air. |
| DENSITY | The amount of mass in a given space; mass per unit volume. |
| PRESSURE | The amount of force pushing on a surface or area. |
| AIR PRESSURE | A force that is the result of the weight of a column of air pushing down on an area. |
| BAROMETER | An instrument used to measure changes in air pressure. |
| MERCURY BAROMETER | An instrument that measures changes in air pressure, consisting of a glass tube part filled with mercury, with its open end resting in a dish of mercury. Air pressure pushing on the mercury in the dish forces the mercury in the tube higher. |
| ANEROID BAROMETER | An instrument that measures changes in air pressure without using liquid. Changes in the shape of an airtight metal box cause a needle on the barometer dial to move. |
| ALTITUDE | Elevation above sea level. |
| TROPOSPHERE | The lowest layer of Earth's atmosphere, where weather occurs. |
| STRATOSPHERE | The second-lowest layer of Earth's atmosphere; the ozone layer is located in the upper stratosphere. |
| MESOSPHERE | The middle layer of Earth's atmosphere; the layer in which most meteoroids burn up. |
| THERMOSPHERE | The outermost layer of Earth's atmosphere. |
| IONOSPHERE | The lower part of the thermosphere, where electrically charged particles called ions are found. |
| AURORA BOREALIS | A colorful, glowing display in the sky caused when particles from the sun strike oxygen and nitrogen atoms in the ionosphere; also called the Northern Lights. In the Southern Hemisphere they are call Australis Borealis or Southern Lights. |
| EXOSPHERE | The outer layer of the thermosphere, extending outward onto space. |
