Environmental Chemistry

What is Environmental Chemistry? 

Environmental chemistry is a branch of chemistry which deals with the study of various chemical and biochemical processes that occur in the environment. In environmental chemistry, we also study the effect of human activities on the environment. 


Environmental Pollution 

When physical and biological components of the environment get contaminated up to such extent that they start affecting the natural environmental processes and composition adversely, then this condition is called environmental pollution. 

The substances which cause pollution are called pollutants. 

Pollutants cannot be degraded by natural processes and remain in the environment for a long time and unbalance the composition of the environment which causes adverse effects on its natural processes. In the end, when these natural environmental processes get adversely affected, then they impose adverse effects on human beings as well. The irony is these pollutants originate from the various human activities such as overuse of plastic bags, over emission of carbon dioxide through factories and power plants etc. 


Atmospheric Pollution 

The envelope of gases which surrounds the earth is called its atmosphere. 

Earth’s atmosphere does not have the same composition in all regions. Its thickness and density vary at all heights. It has been divided into various layers and different gases are found in different layers. 

Various physical and chemical processes add various harmful gases and unbalance the composition of air. This causes atmospheric pollution. 

Atmosphere has been divided into following six layers –

  • Troposphere 

  • Stratosphere 

  • Mesosphere 

  • Thermosphere 

  • Ionosphere 

  • Exosphere 

Troposphere starts at the surface of the earth and extends up to 14.5 km height from sea level. Thus, it is the lowest region of the atmosphere where living organisms and human beings live. Above the troposphere, stratosphere starts. It ranges between 10 – 50 km from the sea level. 


Following Major Pollutants are Found in the Troposphere –

Type of Pollutant 

Name of Pollutants 

Sources 

Gaseous Air Pollutants 

Oxides of Sulphur – SO2, SO3 etc. 

Factories, power plants, pesticides, insecticides, mismanagement of waste materials, cars, buses, trucks, oil refineries, industrial waste etc. 

Oxides of nitrogen – NO, NO2, NO3 etc. 

Hydrocarbons – CH4, coke, other petroleum products etc. (they form pollutants due to their incomplete combustion) 

Oxides of carbon- CO2 (Greenhouse gas), CO 

Particulate Pollutants 

Smoke – combustion of organic matter, burning of fossil fuel, dry leaves, garbage etc. 

Methods of extraction of metals, cigarettes, some agricultural techniques such as threshing, spray of herbicides, pesticides, insecticides etc.   

Dust – crushing and grinding of solid materials, extraction of metals etc. 

Mists – sulfuric acid mist, spray of herbicides and insecticides etc. 

Fumes – sublimation, boiling, distillation of organic solvents and metals form fume particles. 


Global Warming and Greenhouse Effect 

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Almost 75% of the heat energy from the Sun reaching to the earth can be absorbed by the surface of the earth. Rest of the solar radiation or heat energy radiates back to the atmosphere. This absorbed heat energy increases the temperature of the earth. The heat radiations which are going back to the atmosphere get trapped by the carbon dioxide, methane, ozone, CFC compounds etc. Thus, this heat increases the temperature of the atmosphere. If the amount of these gases increases in the atmosphere, then more heat gets absorbed by these gases and the atmosphere becomes hotter. This is called global warming. This happens exactly like the greenhouse effect. In colder places plants are grown in a greenhouse in which solar radiations can enter the glass walls but the heat radiations from the greenhouse cannot go back. Thus, the heat gets trapped in the greenhouse and plants get enough solar heat to grow. But the greenhouse effect on earth’s surface causes global warming which is harmful for us and for the environment. 

Industrial waste, burning fossil fuels etc. activities of human beings are increasing the concentration of greenhouse gases such as CO2, ozone, CFCs etc. in the environment. It is a point of concern as due to the increasing amount of greenhouse gases global warming is also increasing which is increasing the temperature of the earth. 

The ozone hole – Depletion of the ozone layer over the south pole is commonly known as ozone hole. Increasing concentration of chlorofluorocarbons in the atmosphere are the main cause behind ozone layer depletion. Ozone layers filter the UV radiations. Ozone layer depletion causes UV radiations to enter the earth’s atmosphere. UV radiations cause skin cancer, kill phytoplanktons, damage fish productivity etc. 

Acid Rain - In simple words, if rainwater has pH lower than 5.7 then it is called acid rain. According to EPA (Environmental Protection Agency) acid rain is a broad term which includes any form of precipitation with acidic components (nitric acid, sulfuric acid etc.) that fall to the ground. It can be in the form of wet or dry forms. It includes rain, fog, hail or even dust that is acidic.


Chemistry Behind Acid Rain 

Industries, vehicles etc. emit gases such as sulfur dioxide, nitrogen oxides etc. which are transported by wind and air currents and react with rainwater. When sulfur dioxide and nitrogen oxides (NO2, NO3) react with water, form acids (such as sulfuric acid, nitric acid etc.). Other than sulfur dioxide and nitrogen oxides, carbon dioxide present in the atmosphere also contributes to acid rain. 

Reactions involved in formation of acid rain can be written as follows –

S + O2 🡪 SO2

N + O2 🡪 NO2

C + O2 🡪 CO2

SO2 + H2O 🡪 H2SO3

2H2SO3 + O2 🡪 2H2SO4

2NO2 + H2O 🡪 HNO3 + HNO2

2HNO2 + O2 🡪 2HNO3

CO2 + H2O 🡪 H2CO3 

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Rainwater has a pH of 5.7 which is slightly acidic because of carbonic acid formed by the reaction of carbon dioxide with water, present in it. It doesn’t lower the pH of water much as carbonic acid is a weak acid. But when sulfuric acid and nitric acid get merged with rainwater, they lower the pH of rainwater below 5.7 as these both are strong acids. 


Causes of Acid Rain 

All those mediums, instruments or reactions which emit gases such as sulfur dioxide, nitrogen oxides etc. are indirect causes of acid rain. Here we are listing few causes of acid rain –

  • Natural causes- Forest fires, volcanic eruptions etc. release some chemicals which cause acid rain. Although these natural incidents cause only 1% of the total amount of acid rains. Major part of acid rain is caused by human activities only. 

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Forest Fire: Emitting Air Polluting Gases

  • Industries – Steel industry, cement manufacturing industry etc. emit sulfur dioxide, nitrogen oxides in large quantity which causes acid rain. 

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Industrial Emission: NO2 + SO2

  • Coal based power plants – Coal based power plants emit many gases which causes air pollution and acid rain. 

  • Burning of fossil fuels – Fuels which are produced by the anaerobic decomposition of dead organisms are called fossil fuels. Burning of fossil fuels such as coal, petrol etc. emit many gases which cause air pollution and air pollution is the main cause of acid rain.

  • Petrol and diesel-based vehicles – Petrol and diesel on burning produce a large amount of carbon dioxide, sulfur dioxide and nitrogen oxides which cause air pollution and acid rain. 

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Emission by Petrol and Diesel Based vehicles


Effects of Acid Rain 

Acid rain mainly affects our ecosystem, health, materials such as marble, visibility etc. We can list effects of acid rain by following points –

  • Effect of acid rain on our ecosystem- Ecosystem is a community made by interaction between living organisms and their physical environment. All living and non-living material is interlinked. If one part of it gets affected, then another part also gets the harmful effects of it. Due to acid rain organisms which live in the pond, sea etc. get affected at a large level. If pH level goes below 5.7 then frogs, fishes, snails, clams, trout etc. die. 

Acid rainwater releases aluminum from soil which goes into lakes, sea and ponds. Thus, more acid rain causes high amounts of aluminum in water bodies while most of the plants and animals can tolerate a moderate amount of aluminum. So, many plants and animals die due to this. 

  • Effect of acid rain on human health – Human health gets adversely affected by acid rain. Human beings are also a part of the ecosystem. Acid rain causes imbalance in the ecosystem by affecting its many factors. It can cause lung diseases, hair fall, liver diseases etc. 

  • Effects of acid rain on material – Acid rain affects the materials such as marble, cement buildings etc. Strong acids present in the acid rain react with calcium carbonate and other materials which cause damage on their surface. They get faint and deteriorate faster. 

  • Less Visibility - Gases such as sulfur dioxide, carbon dioxide etc. cause fog, smog in the atmosphere which causes less visibility. 

  • Effect of acid rain on plants, trees and forests – Acid rain adversely affects forests, plants and trees. They die due to high amounts of aluminum in the soil or acid in the water. Their roots get dry completely and ultimately the plant or tree dies. 


Effect of Acid Rain on Monuments (Real – Life Examples)

  • Taj Mahal – Taj mahal is largely affected by the acid rain. Sulphuric acid reacts with marble or calcium carbonate and forms calcium sulfate. Which cause corrosion. Thus, white color of the marble gets brownish. Reaction can be written as follows –

CaCO3 + H2SO4 🡪 CaSO4 + H2O + CO2

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Effect of acid rain on Taj Mahal 

  • Statue of Liberty – It is made up of copper. It is becoming green in colour due to reaction with acid present in acid rain. Reaction can be written as follows –

Cu + 2H2SO4 🡪 CuSO4 + SO2 + 2H2O

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Effect of Acid Rain & oxidation on Statue of Liberty


Prevention of Acid Rain 

Following measures should be taken for prevention of acid rain –

  • Air pollution should be reduced. 

  • Emission of air polluting gases such as sulfur dioxide, nitrogen dioxide etc. should be reduced or stopped. 

  • Electric vehicles should be used in place of fossil fuels-based vehicles. 

  • Industries must use different ways to prevent emission of air polluting gases. 

  • Burning of fossil fuels should be minimized. 


Water Pollution 

Contamination of water bodies due to various human activities such as industrial waste, mining activities, sewage wastewater etc. is called water pollution. 


Soil Pollution 

Contamination of soil due to agricultural waste, insecticides, detergent industries, chemical industries etc. is called soil pollution. 


Industrial Waste 

Industrial waste is the main cause of environmental pollution. Industries generate solid, liquid and gaseous waste materials. Industrial waste can be of two types biodegradable and non – biodegradable. Non - biodegradable industrial waste generally remains in the environment for a long time. It is generated mainly by thermal power plants. 

Industrial waste must be managed effectively to reduce the air, soil and water pollution. Effective management of the industrial waste can reduce the pollution caused by industrial waste by 70%. Thus, management of the industrial waste is of utmost importance. Large parts of the industrial waste can also be recycled and reused. 


Strategies to Control Environmental Pollution 

Following strategies can be helpful to control the environmental pollution –

  • General awareness regarding environmental pollution is a must as it will make people aware that their activities are causing harm to the environment and mankind. 

  • An effective and well managed waste management system is required to deal with solid, liquid and gaseous waste. 

  • Proper collection and disposal should be done of domestic dry and wet waste. 

  • Methods of 3Rs (reduce, reuse and recycle) should be used. 


Green Chemistry 

Overuse of fertilizers, weedicides etc. for a long time causes damage to the soil. Over exploitation of the soil makes it infertile. This problem gave birth to green chemistry as a solution. Green chemistry is a way of thinking and is about utilizing the existing knowledge and principles of chemistry and other sciences to reduce the adverse impact on the environment. Green chemistry is a production process that would bring about minimum pollution or deterioration to the environment.  

This ends our coverage on the summary of the unit “Environmental Chemistry”. We hope you enjoyed learning and were able to grasp the concepts. You can get separate articles as well on various subtopics of this unit such as soil pollution, water pollution etc. on Vedantu website. We hope after reading this article you will be able to solve problems based on the topic. We have already provided detailed study notes or revision notes for this unit, which you can easily download by registering yourself on Vedantu website. Here in this article we have discussed the unit in a summarized way with the emphasis on important topics of the unit.  If you are looking for solutions of NCERT Textbook problems based on this topic, then log on to Vedantu website or download Vedantu Learning App. By doing so, you will be able to access free PDFs of NCERT Solutions as well as Revision notes, Mock Tests and much more.