From the beginning of civilization, human beings have used various natural resources for their benefits, creating conveniences that make the most of many of the Earth’s energy resources in order of making life easier.

While these developments have made our lives easier we can all agree that industrialization has resulted in pollution by the release of harmful substances into the environment. The major contributors, called precursors to acid rain are emissions of sulphur dioxide (SO2) and nitrogen oxides (NOx) – nitric oxide (NO) and nitrogen dioxide (NO2) and to a smaller extent of carbon dioxide (CO2).

  • nitrogen oxides – Nitrogen oxides (NOx) consist of nitric oxide (NO), nitrogen dioxide (NO2) and nitrous oxide (N2O) and are formed when nitrogen (N2) combines with oxygen (O2). The lifespan of nitric oxide and nitrogen dioxide in the atmosphere range from one to seven days as oppose to up to 170 years for nitrous oxide.  Nitric oxide has no colour, odour, or taste and is non-toxic. In the air it is rapidly oxidized to nitrogen dioxide.Nitrogen dioxide is a reddish-brown gas with a pungent, irritating odour. It absorbs light and leads to the yellow-brown haze sometimes seen hanging over cities. It is one of the main components of smog.Nitrous oxides is naturally present in the atmosphere as part of the Earth’s nitrogen cycle, and has a variety of natural sources and results from bacterial processes, biological growth and decay, lighting and forest and grassland fires.However, human activities such as agricultural, fossil fuel combustion, waste water management and industrial processes are increasing the amounts of N2O in the atmosphere. Note, that agriculture plays a role in nitrogen oxide emissions with the use of fertilizer contributing nitrous oxide to the atmosphere.
  • sulfur dioxide (SO2) – SO2 is a dense, colourless gas formed when many sulphur compounds are burnt in air. It is also very toxic, and has a suffocating odour. SO2 occurs naturally as one of the decay products of plant and animal matter, and is also one of the gases which are emitted from volcanoes.  Man-made sources include sour gas processing, oil sands production, coal combustion, ore refining, chemical manufacturing and other fossil fuel processing burning.

These substances are released into the environment from burning of oil and coal by plants and factories, homes and cars which are considered the main source of chemicals that cause acid rain, although some air pollution comes from natural sources, most is as a result of human activities.

Now acid rain in its simplest term is a rain or any other form of precipitation that is unusually acidic, meaning that it possesses elevated levels of hydrogen ions.


Understand that acid rain is made when pollutants arise from the use of coal in the production of electricity, from base metal smelting and from fuel combustion in vehicles.   When these gases are discharged into the atmosphere they react with the water, oxygen and other gases already present to form sulphuric acid, ammonium nitrate and nitric acid.

Once the sulphur and nitrogen oxides from these man-made causes are released into the air they are caught by wind currents and wind pattern and are blown hundreds of miles away falling back to the ground as acid rain or other forms of precipitation. Since the gas pollutants drift along in clouds they mix with moisture in the atmosphere caused by rain eventually converting sulphuric dioxide into sulphuric acid, and the nitrogen oxide into nitric acid.

It is worth noting, that acid precipitation and water droplets in the air and in clouds are highly affected by the form of precipitation and amount of water vapour in the air. Generally, water would be less acidic, the more drops there is, since the acid particles are dissolved and diluted.  Also, the more precipitation and the faster it falls, the less acidic the rain water, because of the dilution factor.

forest damaged by acid rain one of the main effect of acid rain 

During rapid rainfall such as a thunder storm the air “cleans”, causing most of the pollutants to wash out and temporarily cleaning the air. This system works strategically to protect the environment constantly fighting the force of human factors.

Acid precipitation is affected by how much sulphur and nitrogen bearing pollution and soil in the air. Soil generally helps to neutralize the acidic pollution in rain, where soil is alkaline and where it is windy (so that soil becomes airborne), generally have less acidic precipitation as a result.

Acid rain, acid fog and acid mist all fall in the category of acid deposition.  This primarily concerned with the long-range as opposed to local effects simply because the pollutants are mixed into the atmosphere and therefore can be difficult to link to local attributes or sources

These pollutants are normally more disseminated and of lower concentration than local ground level pollutants. Acid deposition is used to refer to acid rain because this term includes other forms of acidic precipitation such as snow. It is two (2) types of deposition:

dry deposition = dust foil & wet deposition = rainfall 

     Wet Deposition

This refers to acidic rain, fog and snow, occurring when the acid chemical in the air are blown into areas where the weather is wet. The acid then falls to the ground as rain, snow, fog or mist. This acidic water flows over and through the ground severely affecting all living things.

The strength of this effect depends highly on acidity of water, the chemistry and buffering capacity of the soils involved along with the types of fish, trees and other living things that rely and live in and on the water.

Dry Deposition

Dry deposition is the second method of acid deposition. Whilst wet deposition involves the precipitation of acids, dry deposition occurs when the acids are first transformed chemically into gases and salts before falling under the influences of gravity back to Earth. Dry Deposition is highly dependent on the re-activity of gases and the size distribution if the particles along with the surface on which the dry deposition occurs with hilly areas increasing deposition.

Sulphur dioxide for example is deposited as a gas and as salt. SO2 is absorbed by soil, leaves and stones and then is oxidized to acid sulphate, with the rate of adsorption proportionally dependant on the amount of SO2 in the air, types of materials, along with the surface area of the material and weather since wet surfaces removing more sulphur from the atmosphere than dry.

The major environmental pollutants deriving from the advance movement of industrialization is the fact that these pollutants cause acid rain, travel distances meaning that it is a transboundary problem, meaning that acid pollutants are not necessarily deposited in the same country where they were produced, acidic emissions produced by one country can be deposited in another, for example Sweden and Norway, both receive more than 90 percent of their sulphur pollution from abroad and is the main reason this issue is of great concern worldwide.

It is worth continuously noting that rain is one of the most essential ingredients for human and animal life on Earth.  While, most of the Earth’s surface is covered by water most of it we cannot drink, 97% is salty sea water, which is useless to most plants and animals on land, leaving us with only 3% consumable.

rain is everything to all live on Earth 

Hence, the importance of rain to life on Earth, the water provided by rain allows all life on Earth to survive; precipitation provides life on land with salt free water while supporting hydrologic cycle, aquatic life and ground water.



Carter, L, 2013.Acid Rain. [Book Abstract]

National Environmental Forum, 1997. Nitrogen Dioxide. [Report]


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