The emissions are the release of a substance (usually a gas, when referring to the subject of climate change) into the atmosphere.
In order to reduce emissions, modern car engines carefully control the amount of fuel they burn. They try to keep the air-to-fuel ratio very close to the stoichiometric point, which is the ideal ratio of air to fuel.
The main emissions of a car engine are: Nitrogen gas (N2), Carbon dioxide (CO2), Water vapor (H2O)
Because the combustion process is never perfect, some smaller amounts of more harmful emissions are also produced in car engines. Catalytic converters are designed to reduce all three:
- Carbon monoxide (CO) is a poisonous gas that is colorless and odorless.
- Hydrocarbons or volatile organic compounds (VOCs) are a major component of smog produced mostly from evaporated, unburned .fuel.
- Nitrogen oxides (NO and NO2, together called NOx) are a contributor to smog and acid rain, which also causes irritation to human mucus membranes.
These emissions are mostly benign, although carbon dioxide emissions are believed to contribute to global warming.