| A | B |
|---|
| Weather | The condition of Earth‘s atmosphere at a particular time and place. |
| Atmosphere | The envelope of gases that surrounds Earth. |
| Ozone | A form of oxygen that has three oxygen atoms in each molecule instead of the usual two. |
| Water Vapor | Water in the form of a gas. |
| Density | The amount of mass of a substance in a given volume. |
| Pressure | The amount of force pushing on an area. |
| Air Pressure | The pressure caused by 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 partially filled with mercury, with its open end resting in a dish of mercury. |
| Aneroid Barometer | An instrument that measures changes in air pressure without using a liquid. |
| Altitude | Elevation above sea level. |
| Troposphere | The lowest layer of Earth’s atmosphere. |
| Stratosphere | The second-lowest layer of Earth’s atmosphere. |
| Mesosphere | The layer of Earth’s atmosphere immediately above the stratosphere. |
| Thermosphere | The outermost layer of Earth’s atmosphere. |
| Ionosphere | The lower part of the thermosphere. |
| Exosphere | The outer layer of the thermosphere. |
| Pollutants | Harmful substances in air, water, or soil. |
| Photochemical Smog | A brownish haze that is a mixture of ozone and other chemicals, formed when pollutants react with each other in the presence of sunlight. |
| Acid Rain | Rain that contains more acid than normal. |
