Environmental Hazards & Disasters – UGC NET – Geography – Solved PYQs

1. Certain substances are classified as water pollutants, others as air pollutants and still others as land pollutants. Which one of the following pollutes three parts of our environment? (SEPT 2013)

(1) Fluorocarbons
(2) Smog
(3) Acid rain
(4) Ozone

Correct Answer: (3) Acid rain

Explanation:

Acid rain is one of the few forms of pollution that affects all three major components of the environment—air, water, and land. It is formed when pollutants such as sulphur dioxide (SO₂) and nitrogen oxides (NOₓ) released from industries, thermal power plants, and vehicles react with water vapor and other atmospheric constituents to produce sulphuric acid and nitric acid. These acidic compounds are then deposited on the Earth’s surface through rain, snow, fog, or dry deposition.

Acid rain is considered an air pollutant because its formation occurs in the atmosphere through chemical reactions involving gaseous pollutants. It becomes a water pollutant when acidic precipitation enters rivers, lakes, ponds, wetlands, and groundwater systems, lowering the pH of water bodies and adversely affecting aquatic organisms. Fish, amphibians, and other aquatic species may experience reduced survival and reproductive success in acidified waters.

Acid rain also acts as a land pollutant by altering soil chemistry. It can leach essential nutrients such as calcium, magnesium, and potassium from the soil while increasing the availability of toxic metals like aluminum. These changes reduce soil fertility and can damage forests, crops, and natural vegetation. Acid deposition is also responsible for the deterioration of buildings, monuments, and cultural heritage structures, especially those made of limestone and marble.

Fluorocarbons, particularly chlorofluorocarbons (CFCs), are primarily associated with atmospheric pollution and ozone depletion. Smog is mainly an air pollution phenomenon resulting from the interaction of pollutants in the atmosphere. Ozone can be beneficial in the stratosphere where it protects life from harmful ultraviolet radiation, while ground-level ozone is a significant air pollutant, but it is not typically classified as simultaneously polluting air, water, and land.

The widespread environmental impact of acid rain across atmospheric, terrestrial, and aquatic systems makes it a classic example of a pollutant affecting all three major components of the environment.

2. The main source of carbon monoxides, as air pollutants, is (JUNE 2014)

(1) Thermal decomposition of fats
(2) Dye-making
(3) Blast furnaces
(4) Gasoline motor exhausts

Correct Answer: (4) Gasoline motor exhausts

Explanation:

Carbon monoxide (CO) is a colorless, odorless, and highly toxic gas produced mainly by the incomplete combustion of carbon-containing fuels. Among the various sources of carbon monoxide in the atmosphere, gasoline motor exhausts are recognized as the major contributor, especially in urban and industrialized regions where large numbers of vehicles operate daily.

In gasoline-powered engines, fuel does not always burn completely because of limited oxygen availability and imperfect combustion conditions. As a result, a significant amount of carbon in the fuel is converted into carbon monoxide instead of carbon dioxide (CO₂). Automobiles, motorcycles, trucks, and other gasoline-powered vehicles collectively release large quantities of carbon monoxide into the atmosphere, making transportation one of the most important sources of this pollutant.

Carbon monoxide poses serious health risks because it readily combines with hemoglobin in the blood to form carboxyhemoglobin. This compound reduces the oxygen-carrying capacity of blood, leading to oxygen deficiency in body tissues. Exposure to elevated concentrations can cause headaches, dizziness, fatigue, impaired vision, respiratory distress, unconsciousness, and, in severe cases, death.

Blast furnaces and certain industrial processes also emit carbon monoxide, but their contribution to overall atmospheric carbon monoxide pollution is generally lower than that of motor vehicle emissions. Thermal decomposition of fats and dye-making are not considered major sources of carbon monoxide pollution on a global or urban scale.

The introduction of technologies such as catalytic converters, improved engine design, cleaner fuels, and stricter vehicle emission standards has helped reduce carbon monoxide emissions in many countries. Despite these improvements, vehicular exhaust remains one of the most significant sources of carbon monoxide in urban environments and is a major concern in studies of air pollution and environmental health.

3. Given below are two statements, one labelled as Assertion (A) and the other labelled as Reason (R). Select your answer from the codes given below. (DEC 2014)

Assertion (A): Deforestation results in the increase of concentration of carbon dioxide in the atmosphere.

Reason (R): Forests utilize carbon dioxide during the process of photosynthesis for manufacturing of food.

Codes

(1) Both (A) and (R) are true and (R) is the correct explanation of (A)
(2) Both (A) and (R) are true, but (R) is not the correct explanation of (A)
(3) (A) is true, but (R) is false
(4) (A) is false, but (R) is true

Correct Answer: (1) Both (A) and (R) are true and (R) is the correct explanation of (A)

Explanation:

The Assertion (A) is true because deforestation leads to an increase in the concentration of carbon dioxide (CO₂) in the atmosphere. Forests act as major carbon sinks, absorbing large quantities of atmospheric carbon dioxide and storing carbon in plant biomass, roots, litter, and soil. When forests are cut down, burned, or degraded, their capacity to absorb carbon dioxide is reduced. In addition, the carbon stored in trees is often released back into the atmosphere through burning, decomposition, or land-use changes, contributing further to the rise in atmospheric CO₂ levels.

The Reason (R) is also true because forests utilize carbon dioxide during photosynthesis. Green plants absorb carbon dioxide from the atmosphere and combine it with water in the presence of sunlight to produce carbohydrates, which serve as food and energy reserves for growth and development. Oxygen is released as a by-product of this process. Through continuous photosynthesis, forests remove substantial amounts of carbon dioxide from the atmosphere and play a crucial role in regulating the global carbon cycle.

The reason correctly explains the assertion. Since forests absorb carbon dioxide through photosynthesis, the removal of forest cover decreases the rate of carbon dioxide uptake. As a result, more carbon dioxide remains in the atmosphere, leading to increased concentrations of this important greenhouse gas. Elevated atmospheric carbon dioxide levels contribute to the greenhouse effect, global warming, and broader climate change impacts.

Forests are among the most effective natural systems for carbon sequestration. Tropical rainforests, temperate forests, and boreal forests collectively store enormous quantities of carbon and help maintain the balance of atmospheric gases. Large-scale deforestation not only reduces biodiversity and ecosystem stability but also weakens one of the planet’s most important mechanisms for regulating atmospheric carbon dioxide concentrations.