| A | B |
|---|
| Weather | the condition of Earths atmosphere at a particular time and place (p.14) |
| Atmosphere | the layer of gases that surrounds Earth (p.14) |
| Ozone | a form of oxygen that has three oxygen atoms in each molecule instead of the usual two (p.16) |
| Water vapor | water in the form of a gas (p.17) |
| Pollutant | harmful substances in the air |
| Photochemical smog | a browning haze that is a mixture of ozone and other chemicals |
| Acid rain | rain that contains more acid than normal (p.23) |
| Density | the amount of mass of a substance in a given volume (p.25) |
| Pressure | the force pushing on an area or surface (p.25) |
| Air pressure | a force that is the result of the weight of a column of air pushing down on an area (p.26) |
| Barometer | an instrument used to measure changes in air pressure (p.26) |
| Mercury barometer | an instrument that measures changes in air pressure with a glass tube partially filled with mercury |
| Aneroid barometer | an instrument that measures changes in air pressure without using a liquid. Changes in the shape of an airtight metal box cause a needle on the barometer dial to move (p.27) |
| Altitude | elevation above sea level (p.28) |
| Troposphere | the lower layer of Earths atmosphere; where weather occurs (p.31) |
| Stratosphere | the secomd lowest layer of Earths atmosphere; where the ozone is located (p.32) |
| Mesosphere | the middle layer of Earths atmosphere; the layer in which most meteoroids burn up (p.32) |
| Thermosphere | the outermost layer of Earths atmosphere (p.35) |
| Ionosphere | the lower part of the thermosphere |
| Exosphere | the outer layer of the thermosphere |
