Acid rain refers to any precipitation (rain, fog, mist, snow, smoke, dust) that is more acidic than normal (pH of less than 5.6)
Acid rain is caused by atmospheric pollution from acidic gases such as Sulphur dioxide and oxides of nitrogen
Wet deposition: If the acid chemicals in the air are blown into areas where the weather is wet, the acids can fall to the ground in the form of rain, snow, fog, or mist.
Dry deposition: In areas where the weather is dry, the acid chemicals may become incorporated into dust or smoke and fall to the ground through dry deposition, sticking to the ground, buildings, vegetation, cars, etc

Acidic gases	Source
SO. (Sulphur oxides)	Fossil fuel burning, power plants, smelting of metal sulfide ores, paper production Industrial production of sulfuric acid in metallurgical, chemical and fertilizer industries Natural: volcanoes, seas and oceans, decomposition of organic matter.
NO. (Nitrogen oxides)	Fossil fuel burning, biomass burning, forest fires, power plants, fertilizers, production of adipic acid Natural: lightening, oceans
Formic acid (HCOOH)	Biomass burning due to forest fires causes emission of formic acid (HCOOH) and formaldehyde (HCHO) into the atmosphere. Large fraction formaldehyde gets photo-oxidation and forms formic acid in the atmosphere.

Chlorine
Phosphoric Acid
Hydro Chloric Acid
CO2 (Carbon dioxide)	Fossil fuel burning, industrial process, respiration.
CO (Carbon monoxide)	Biomass burning, exhaust, Industrial sources: smelting of iron ore, Biogenesis, Plant isoprene’s.
CH4 (Methane)	Paddy fields, wetlands, gas drilling, landfills, decomposition of animals wastes and carcasses.
Carbonic acid (H2CO3)	Carbon monoxide and carbon dioxide dissolve in water (water vapor) to form carbonic acid.

Concentrated in the industrialized belt of the northern hemisphere.
often upland and/or mountainous areas, which are well-watered by rain and snow.
Many parts of Scandinavia, Canada, the North and Northeast United States and Northern Europe (particularly West Germany and upland Britain)
number of acid rain hot spots including Nova Scotia, Southern Ontario and Quebec in Canada, the Adirondack Mountains in New York, Great Smoky mountains, parts of Wisconsin, Minnesota, and the Colorado Rockies of the US.
In India, Lowering of soil pH is reported from north-eastern India, coastal Karnataka and Kerala, parts of Orissa, West Bengal and Bihar.

NOTE: Salinity is observed in Punjab and Haryana plains , alkalinity (excessively irrigated regions of Punjab, Haryana, Karnataka)

Sources that cause Acid rains are often transported to far distances away from their place of genesis and hence Acid rains are also experienced at remote locations

The atmosphere receives oxides of sulfur and nitrogen from natural and man-made sources.

Some of these oxides fall back directly to the ground as dry deposition, either close to the place of origin or some distance away.

Sunlight stimulates the formation of photo-oxidants (such as ozone) in the atmosphere.

These photo-oxidants interact with the oxides of sulfur, nitrogen, other gases (like NH3) to produce H2SO4 (Sulphuric acid) and HNO3 (nitric acid) by oxidation.
Acid rain containing ions of sulfate, nitrate, ammonium and hydrogen falls as wet deposition

Optimum pH of most bacteria is near neutrality. Blue-green Bacteria prefers more alkaline environment while fungi prefers more acidic environment
Lichens serve as good bio-indicators for air pollution (especially sulphur dioxide)
Anthropogenically acidified lakes looks clear because of low primary productivity while naturally acidified lakes looks brown to yellow colour because of humic substance

Leaching of nutrients
Decrease in respiration of soil organisms
Low rate of decomposition (bacteria prefers near neutrality pH levels)
Impact of Acid rains on Indian soils is less since they are mostly alkaline and have good buffering ability

Chronic bronchitis
Irritation on skin and eyes
Increased cadmium, lead levels, asbestos and decreased aluminum levels in the body

Material	Type of Impact	Principal Air Pollutants
Metals	Corrosion, tarnishing	Sulphur Oxides and other acid gases
Paints and organic coatings	Surface erosion, discoloration, soiling	Sulphur dioxides, hydrogen sulphide
Textiles	Fading, colour change	Nitrogen oxides, ozone
Leather	Weakening, powdered surface	Sulphur oxides
Rubber	Cracking	Ozone

Acid rain corrodes the marble monuments like Taj Mahal. This phenomenon is called as � Marble cancer”

Acid Rain