Engine emissions are exhaust gases that are released from an engine after fuel combustion. They can be particulate or gaseous and include carbon dioxide (CO2), water vapor, and other compounds.  Engine emissions can include: Particulate matter (PM): A mixture of soot and other solid and liquid materials, such as heavy hydrocarbons. Nitrogen oxides (NOx): A primary ingredient in smog that forms when nitrogen is released during combustion and combines with oxygen. Carbon monoxide: A toxic compound that can affect the bloodstream and cause complications for people with heart... Show more

Engine emissions are exhaust gases that are released from an engine after fuel combustion. They can be particulate or gaseous and include carbon dioxide (CO2), water vapor, and other compounds. 

Engine emissions can include:
Particulate matter (PM): A mixture of soot and other solid and liquid materials, such as heavy hydrocarbons.
Nitrogen oxides (NOx): A primary ingredient in smog that forms when nitrogen is released during combustion and combines with oxygen.
Carbon monoxide: A toxic compound that can affect the bloodstream and cause complications for people with heart conditions.
Hydrocarbons: Released when fuel burns in an internal combustion engine. 

The main products of the complete combustion of petroleum-based fuels in an internal combustion engine are carbon dioxide (13%) and water (13%). 

The emission light on a car may come on for a number of reasons, including:
The engine is burning too much fuel, increasing your carbon footprint
The system is not burning enough fuel
A broken sensor
The car is either running too rich or too lean
There's an issue with the sensor itself

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