Match the following vocabulary with their definitions. 1. emissions a specific source of pollution that is easy to identify, such as a smokestack 2. carbon monoxide occurs when a layer of warm air prevents the rising air from escaping; the polluted air is trapped and held close to Earth’s surface 3. nonpoint source a source that is widely spread and cannot be tied to a specific origin, such as vehicle emissions 4. point source a warning about a type of air pollution called photochemical smog 5. temperature inversion a colorless, odorless gas that is radioactive and is formed naturally by certain rocks underground 6. smog alert gases and particles which are put into the air or emitted by various sources 7. radon a colorless, odorless gas that forms when fuels are not completely burned