Robert Angus Smith of England coined the term acid rain in 1852. Term was recognized in 1972 after 20 years and slowly the western industrial world became more and more familiar with this term. It literally implies a change toward more acidic conditions of rain, fog or snow affecting the lakes, rivers, ground water, soil and forest land. Such changes may occur as a result of slow geo-biological processes occurring in nature or faster episodic emissions from volcanic eruptions. Of late, rapid industrialization all over the globe has resulted in acid forming gases into the atmosphere. In sixties and seventies this phenomenon assumed alarming proportion affecting the main industrial countries of North America and Europe ignoring national and international boundaries. The nature and volume of acid precursor gases evolved from different countries and their trans-boundary movements horrified the western world and their conscious and concerted efforts could arrest the damage in time. These measures have been effective to some extent but through monitoring and R and D work in this continue to enjoy priority in national and international scenario.

India, a developing country, got into the race of industrialization in the early fifties. Scientists then were somewhat aware of the manifestation of air pollution originating from industrialization resulting in the rain water acidity. Scanty efforts to monitor acid rain started in 1950s. Mukharjee documented the hydrogen ion concentration of monsoon rainwater rainwater at Calcutta. Since Calcutta was an industrial city it was not the ideal site for such measurements. A comparatively better site was chosen inside inside Jadavpur university campus. It was observed that there was no factory to the south or south-west of the site since prevailing wind at Calcutta was southerly. It was established that natural rainwater has a pH of 5.7 due dissolved CO2  in water scavenged from air/atmosphere.

The author from his observations concluded that (a) monsoon rain water is neutral under local condition (b) rain water dissolves little carbon dioxide and the dissolved gas is not in equilibrium with atmospheric carbon dioxide.