80% of automobiles exhaust is carbon monoxide. It is a colourless, odourless gas. When inhaled this gas combines with blood haemoglobin about 200 times faster than does oxygen and results in oxygen deficiency. Sulphur dioxide released from chimneys of factories is an important pollutant. In higher concentration SO2 may cause death of cells. Its major effects are damage of membrane, plasmolysis, chlorphyll destruction etc. Oxides of nitrogen are emitted in several forms e.g., NO and NO2 . The nitrogen oxides cause irritation of eyes, nose, throat and lungs. Carbon dioxide in normal concentration is not a pollutant but in higher concentration cause green house effect.