Environmental Chemistry

Environmental Chemistry is the discipline which deals with:

• the environmental impact of pollutants

• the reduction of contamination

• management of the environment

Environmental Chemistry is thus the study of the behaviour of pollutants with respect to their environmental fate and effects on the environment.

Tropospheric pollution arises due to the presence of undesirable substances in the lowest layer of the atmosphere. Tropospheric air pollution has impacts on scales ranging from local to global. Reactive intermediates in the oxidation of mixtures of volatile organic compounds (VOCs) and oxides of nitrogen (NOx) play central roles: the hydroxyl radical (OH), during the day; the nitrate radical (NO₃), at night; and ozone (O₃), which contributes during the day and night. Oxides of sulphur, nitrogen, carbon, and hydrocarbons are the major gaseous pollutants.

Oxides of sulphur (SO₂ and SO₃) and nitrogen (NO₂, NO) are produced as a result of the burning of fossil fuels (coal, automobile fuel). These oxides react with water in the presence of atmospheric oxygen to form nitric acid (HNO₃) and sulphuric acid (H₂SO₄), which leads to the formation of ‘Acid rain’. Acid rain causes harm to agriculture, plants, and trees. It also leads to various respiratory

ailments.

The effects of tropospheric pollution are:

1) They cause respiratory disease like asthma, bronchitis, irritation & redness in the eyes. Increase in levels of carbon monoxide leads to a headache, nervousness and cardiovascular diseases.

2) Increase in Carbon dioxide level leads to global warming and can disturb the balance in the atmosphere.

The particulate pollutants lead to the development of photo chemical smog and act as eye irritants. They also irritate nose and throat and causes chest pain, dryness of throat and cough etc.

The effect of pollution is showing its ill-effects in major cities where pollution is on the high. In the capital city, Delhi, even though measures are taken it has become difficult to bring the pollution levels down. Sustainable development and use of green chemistry can further help in resolving these issues to an extent.

The two gases that are emitted during the combustion of various fuels:

1. Carbon dioxide (CO₂) : Nox- toxic

2. Carbon monoxide (CO): Carbon monoxide is poisonous & toxic.

Carbon monoxide is poisonous because it is capable of forming a complex with haemoglobin (carboxyhaemoglobin), which is more stable than the oxygen-haemoglobin complex. The concentration range of 3–4% of carboxyhaemoglobin decreases the oxygen carrying capacity of blood. This results in headaches, weak eyesight, nervousness, and cardiovascular disorders. A more increased concentration may even lead to death. However, CO₂ is more tolerable in a human body because we are able to exhale it. And it doesn't have the same chemical properties that CO has. CO₂ doesn't react with the haemoglobin in our blood streams

The major greenhouse gases are:

1) Carbon dioxide (CO₂)

2) Methane (CH₄)

3) Water (H₂O)

4) Nitrous oxide (NO)

5) Ozone (O₃)

6) Chlorofluorocarbons (CFCs)

Acid Rain is actually the by-product of the reaction of oxides of sulphur and nitrogen that gets mixed up with water.

The reaction is as follows:

Acid rain causes damage to buildings and structures made of stone and metal. In India, limestone is a major stone used in the construction of various monuments and statues, including the Taj Mahal.

Acid rain reacts with limestone as:

CaCO₃ + H₂SO₄→ CaSO₄ + H₂O + CO₂

This is due to which the monuments started losing its lustre and shiny appearance.

1. Smog is the type of smoke that has fog in reality.

2. Smog is basically derived from the merging of two words; smoke and fog.

3. Smog is a yellowish or blackish fog formed mainly by a mixture of pollutants in the atmosphere which consists of fine particles and ground-level ozone.

4. Smog which occurs mainly because of air pollution can also be defined as a mixture of various gases with dust and water vapor.

Industrial smog contains two primary components: sulphur dioxide and particulate matter. These combine with the water in the fog to produce acidic precipitation -- sulphur dioxide dissolves in water to form sulfuric acid -- and thick, tar-laden droplets.

The primary pollutant in photochemical smog, on the other hand, is ozone. It is produced when nitrogen oxides and volatile organic compounds in automobile and fossil-fuelled power-plant emissions combine with oxygen in the air in direct sunlight. Whereas industrial smog casts a grey pallor over the areas it affects, the nitrogen dioxide in photochemical smog creates a dingy, brownish haze.

Photochemical smog is formed as a result of the reaction of sunlight with hydrocarbons and nitrogen oxides. Ozone, nitric oxide, acrolein, formaldehyde and peroxyacetyl nitrate (PAN) are common components of photochemical smog.

While ozone is toxic in nature, both NO₂ and O₃ are oxidizing agents. They react with the unburnt hydrocarbons in air to produce formaldehyde, PAN, and acrolein.

Photochemical smog has many adverse effects.

1. When combined with hydrocarbons, the chemicals contained within it form molecules that cause eye irritation.

2. Radicals in the air interfere with the nitrogen cycle by preventing the destruction of ground-level ozone.

3. At higher concentrations, photochemical smog causes chest pain, headaches, throat dryness, and various respiratory ailments.

4. Ground level ozone is also produced which has various effects on the human body.

The control measures:

1. The use of catalytic converters in automobiles is recommended to prevent the release of NO₂ and hydrocarbons into the atmosphere.

2. Plantation of plants such as Pinus, Juniparur, Quercus, Pyrus, and Vitis is also advised as these plants have the capability to metabolize NO₂.

UV reactions on oxygen causes the formation of ozone in the stratosphere.

1.

2.

CFC molecules are made up of chlorine, fluorine and carbon atoms and are extremely stable. This extreme stability allows CFC's to slowly make their way into the stratosphere. This prolonged life in the atmosphere allows them to reach great altitudes where photons are more energetic. When the CFC's come into contact with these high energy photons, their individual components are freed from the whole.

Cl+O₃ → ClO+O₂ (step 1)

ClO+O.→Cl+O₂ (step 2)

O₃ + O.→2O₂ (Overall reaction)

Chlorine is able to destroy so much of the ozone because it acts as a catalyst. Chlorine initiates the breakdown of ozone and combines with a freed oxygen to create two oxygen molecules. After each reaction, chlorine begins the destructive cycle again with another ozone molecule.

Ozone hole is the area of the Earth’s atmosphere where abnormal reductions of ozone occur, it is an annual phenomenon observed during the spring in the Polar Regions and is usually followed by a recovery during the summer. In the measurements made in recent times significant reductions in ozone concentrations in the layer, with special emphasis in the area of Antarctica were discovered.

The effects of ozone hole are:

• A deliberate absorption of this radiation can cause disturbances in the body’s immune system.

• The negative effect on the DNA molecule.

• Attacks vision causing cataracts.

• Damages the chromosomes of the skin and can result in cancer and other conditions.

• Plants can be damaged by a lasting exposure.

• Alter aquatic ecosystems, so necessary for biological balance.

The major causes of water pollution are:

1. Industrial waste: Industries produce a huge amount of waste which contains toxic chemicals and pollutants which can cause air pollution and damage to us and our environment. They contain pollutants such as lead, mercury, sulphur, asbestos, nitrates and many other harmful chemicals.

2. Sewage and waste water: The sewage and waste water that is produced by each household is chemically treated and released into sea with fresh water. The sewage water carries harmful bacteria and chemicals that can cause serious health problems.

3. Mining activities: Mining is the process of crushing the rock and extracting coal and other minerals from underground.

4. Chemical fertilizers and pesticides: Chemical fertilizers and pesticides are used by farmers to protect crops from insects and bacteria’s. They are useful for the plant's growth. However, when these chemicals are mixed up with water produce harmful to plants and animals.

5. Animal waste: The waste produced by animals is washed away into the rivers when it rains.

6. Leakage from the landfills: Landfills are nothing but a huge pile of garbage that produces the awful smell and can be seen across the city. When it rains, the landfills may leak, and the leaking landfills can pollute the underground water with a large variety of contaminants.

7. The burning of fossil fuels: Fossil fuels like coal and oil when burnt produce a substantial amount of ash in the atmosphere. The particles which contain toxic chemicals when mixed with water vapor result in acid rain.

Water pollution arises as a result of various human activities. This includes discharges from wastewater treatment plants, run-off from agricultural fields, storm-water drainage, etc.

Pollutants from these sources enter the water bodies, thereby contaminating the water and rendering it impure. Industries and chemical factories discharge toxic, heavy metals such as Fe, Mn, Al, etc., along with organic wastes into the water. Domestic sewage and animal excreta are also responsible for pathogenic contamination of water. These pollutants make water unfit for

drinking. Therefore, all industrial and chemical discharges should be made free from toxic metals before allowing them to enter a water body. The concentration of these pollutants should be checked regularly. Compost should be preferred over chemical fertilizers in gardens and agricultural fields to avoid harmful chemicals from entering ground water.

Biochemical Oxygen Demand or Biological Oxygen Demand, is a measurement of the amount of dissolved oxygen (DO) that is used by aerobic microorganisms when the decomposing organic matter in water. Biochemical Oxygen Demand is an important water quality parameter because it provides an index to assess the effect discharged wastewater will have in the receiving environment. The higher the BOD value, the greater the amount of organic matter or “food” available for oxygen-consuming bacteria.

The steps to control soil pollution are:

• Disposal of garbage to waste bins rather than dumping on neighbourhood or living environment.

• Development of such pesticides should be encouraged, which may save crops from pests and rodents but should not contaminate the soil with toxic chemicals.

• There should be sufficient duration between the harvesting of crops and time of the last spray of pesticides. This will help in reducing contamination of pesticides, directly to the crop.

• There must be an arrangement for educating farmers regarding the proper use of pesticides and fertilizers.

• Reuse and recycle the plastic and other wastes rather than polluting the environment.

Pesticide is any substance or mixture of substances intended for preventing, destroying, repelling or mitigating any pest. Though often misunderstood to refer only to insecticides, the term pesticide also applies to herbicides, fungicides, and various other substances used to control pests. Pesticides also include plant regulators, defoliants, and desiccants. Aldrin and dieldrin are the names of some common pesticides.

Herbicides prevent or eliminate weeds and thus replace or reduce manual and mechanical weeding. As weeds compete with crops for sunlight, water, and soil nutrients, herbicides can also prevent soil erosion and water loss. sodium chlorate (NaClO₃), sodium arsenite (Na₃AsO₃) are two types of herbicides.

Green chemistry is the design, development, and implementation of chemical products and processes to reduce or eliminate the use and generation of substances hazardous to human health and the environment. In green chemistry, the reactants to be used in chemical reactions are chosen in such a way that the yield of the end products is up to 100%. This prevents or limits chemical pollutants from being introduced into the environment. Thus the chemicals would be sustainable and environmentally friendly.

Earth’s most abundant greenhouse gases are CO₂, CH₄, O₃, CFCs, and water vapour. These gases are present near the Earth’s surface. They absorb solar energy that is radiated back from the surface of the Earth. The absorption of radiation results in the heating up of the atmosphere. Hence, greenhouse gases are essential for maintaining the temperature of the Earth for the existence of life. So, in the absence of greenhouse gases, the average temperature over the earth surface will increase exponentially causing it uninhabitable and barren land.

The reasons may vary. One case can be the BOD level change of the lake water. The abundance of phytoplankton can cause the decrease in oxygen level of water because phytoplankton is degraded by bacteria with the help of dissolved oxygen. Since oxygen demand increases, its harder for the fishes to survive on that condition which may cause their death.

Primarily classify domestic wastes as two types-bio degradable and non-biodegradable types. Biodegradable waste such as leaves, rotten food, etc. should be deposited in landfills, where they get decomposed aerobically and anaerobically into manure. Non-biodegradable waste (which cannot be degraded) such as plastic, glass, metal scraps etc. should be sent for recycling.

The points to be noted are:

• Manures should be produced in deep pits rather than in the surface itself.

• The pits should be better covered so that it won't leak any substances both in water and air.

• Recyclable wastes should be sent to factories to get recycled and used again.