* Carbon dioxide (CO2): A major greenhouse gas.
* Water vapor (H2O): A byproduct of combustion.
* Nitrogen (N2): A major component of air, largely unchanged.
* Carbon monoxide (CO): A toxic and poisonous gas. Modern cars have catalytic converters to minimize this.
* Nitrogen oxides (NOx): Greenhouse gases and air pollutants. Catalytic converters also reduce these.
* Unburnt hydrocarbons (HC): Incomplete combustion products contributing to smog. Again, reduced by catalytic converters.
* Particulate matter (PM): Tiny solid and liquid particles, particularly prevalent in diesel engines, but present in all combustion engines. Filters are used to reduce these.
* Small amounts of other substances: Depending on fuel type and engine condition, trace amounts of other gases and compounds may also be present.
The exact composition and amounts vary depending on the engine's condition, the fuel used, and the effectiveness of emissions control systems.
