1.   Carbon monoxide (CO):

It is colourless, odourless, tasteless gas and is not soluble in water.

Source: CO is produced due to:

(i)     Incomplete combustion of fuels.

(ii)   Automobile exhausts (contribute 70% of atmosphere CO)

(iii) Industrial operation

(iv) Natural activity such as volcanic eruptions, natural gas and marsh gas emissions.

Sinks: sink is a system which absorb, store the pollutants, thereby nullifying its harmful effect.

Micro-organism present in soil act as a major sink for CO (convert it into CO₂).

Effects: the levels of CO present in the urban air do not affect significantly the plants and materials but these levels adversely affect health of human beings.

1.      It causes laziness, exhaustion, headache and even death of human beings.

2.      If inhaled in large amount it readily binds with haemoglobin to form carboxyhaemoglobin thereby impair oxygen-carrying capacity of blood.

                     Hb + O₂  HbO₂              Hb + O₂ (normal reaction)

                                 Hb + CO          HbCO (high CO conc.)

The maximum permissible conc. of CO in air is 40 ppm for an exposure of 6-8 hours. In red lights the conc. can increase to 100 ppm. Cigarette smoke contains more than 400 ppm of CO and smokers frequently have HbCO levels between 5 to 10 percent.

3.      CO impairs a person's time interval discrimination, reduces vision and causes cardiovascular disorders.

Control of CO: CO emission can be controlled by:

(i)     Modification of engine design

(ii)   Use of natural gas, methane and blends of light hydrocarbons.

(iii) Use of two stage catalytic convertors to lower pollution from exhaust gases.