react in presence of NO and sunlight to from ground-level ozone, a major component of smog.
Ozone irritates the eyes,damages the lungs,and aggravates respiratory problems
A number of exhaust hydrocarbons are also toxic,with the potential to cause cancer
Under the high presence and temperature conditions in an engine,nitrogen and oxygen atoms in the air react to from various nitrogen oxides,collectively known as
In those countries which do not yet use unleaded petrol,the addition of alkyl lead additives in motor fuels accounts for an estimated 80-90% of lead in ambient air.
The degree of pollution from this source differs from country to country,depending on motor vehicle density and efficiency of efforts to reduce the lead content of petrol.