ACID DEPOSITION AND THE ENVIRONMENT

1. Global Environmental Issues 

The depletion of the stratospheric ozone layer, climate change, atmospheric acidification, desertification, loss of biodiversity and marine pollution are environmental issues of major concern reflecting the increasing influence of human activities on our fragile ecosystem. 

Why are they called global environmental issues? It is because their impacts and damages affect not only the countries where the problems originate, but go beyond political boundaries and can reach global scale. It is also because their solution requires international efforts.  

Many of these problems are interrelated in a very complex manner. For instance, burning of fossil fuels emit carbon dioxide that contributes to global warming. At the same time it also releases gaseous sulphur dioxide and nitrogen oxides into the atmosphere that are the major precursors of acid deposition. These problems may lead to soil degradation, forest die-back and threaten survival of our wildlife.  

As the world population continues to increase, pollution control presents a major challenge. Large amounts of resources and energy will be required in production to meet growing demands and huge quantities of wastes will be generated. This is one of the major causes of global environmental problems.

2. What is acid deposition? 

The history of acidification began several hundred million years ago. At that time there lived and died plants and animals that over time, were transformed into the material that we now refer to as fossil fuels – coal, oil and natural gas. Over the past couple of hundred years we have been rapidly burning up these stores of organic material. When we burn oil and coal from boilers in factories and power plants or burn fuel in our automobiles, we release into the atmosphere millions of tons of sulphur and nitrogen in the form of sulphur dioxide and nitrogen oxides. These pollutants can be transported over long distances by the wind, undergoing chemical transformation to form sulphuric and nitric acids which return to the ground as acid deposition.

Acid deposition describes a process that is a combination of wet and dry deposition. Most of us are familiar with wet acidic deposition that is commonly referred to as acid rain. However, acid rain is only one component of acid deposition. In the tropics, acid rain accounts for only half of the total amount of acid that return to the earth; the other half is deposited in dry form.  

In the wet deposition process, sulphuric and nitric acids are incorporated into cloud droplets during cloud formation. These raindrops will eventually fall onto the ground in the form of rain and snow. When high concentrations of acid are present, the rain shows strong acidity.  

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