The main emissions of a car engine are:

Gases cars emit

Nitrogen (n2)- Air is 78-percent nitrogen gas, and most of this passes right through the car engine.
Carbon dioxide (Co2)- This is one product of combustion. The carbon in the fuel bonds with the oxygen in the air.
Water vapor (H2O)- This is one product of combustion. The carbon in the fuel bonds with the oxygen in the air.
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.