| A | B |
|---|
| air pollution | A change to the atmosphere that has harmful effects. |
| emissions | Particles and gases released into the air from a smokestack or motor vehicle. |
| photochemical smog | A thick, brown haze formed when certain gases react in sunlight. |
| ozone | A toxic form of oxygen. |
| temperature inversion | Condition in which a layer of warm air traps polluted air close to the Earth's surface. |
| acid rain | Precipitation that is more acidic than normal. |
| ozone layer | The layer of the atmosphere that contains a higher concentration of ozone than the rest of the atmosphere. |
| chlorofluorocarbons | Gases containing chlorine and fluorine (CFCs). |
| greenhouse effect | The trapping of heat by certain gases in the atmosphere. |
| global warming | The theory that increasing carbon dioxide in the atmosphere will raise the Earth's average temperature. |
| groundwater | Water stored in underground layers of soil and rock. |
| drought | A period of less rain than normal. |
| water pollution | A change to water that has a harmful effect. |
| sewage | The water and human wastes that are washed down sinks and toilets. |
| fertilizer | A chemical that provides nutrients to help crops grow better. |
| pesticide | A chemical that kills crop destroying organisms. |
| sediments | Particles of rock and sand. |
| scrubber | A device that uses water droplets to clean smokestack emissions. |
| catalytic converter | A device that reduces carbon monoxide emissions from vehicles. |
| primary treatment | The removal of solid materials from wastewater. |
| secondary treatment | The use of bacteria to break down wastes in wastewater. |
