Our environment today is significantly different from how it was in the past, with noticeable degradation in the quality of air and water. While we can survive for a time without food, clean air is essential for just a few minutes. This highlights the critical importance of clean air and water for human well-being and the environment. Pollution refers to the harmful changes occurring in our surroundings and their negative impact on life.

Air is a mixture of gases, primarily nitrogen (about $78\%$) and oxygen (about $21\%$). Other gases like carbon dioxide, argon, methane, ozone, and water vapour are present in smaller amounts.

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How Does Air Get Polluted?

Air pollution occurs when the air is contaminated by unwanted substances that have harmful effects on both living organisms and non-living things. The substances that contaminate the air are called air pollutants.

Air pollutants can come from two main types of sources:

1. Natural Sources: Examples include smoke and dust from forest fires and volcanic eruptions.
2. Human Activities: These are major contributors to air pollution. Sources include:
   • Emissions from factories and power plants.
   • Exhaust from automobiles (vehicles).
   • Burning of firewood and dung cakes (especially in rural areas).

The rapidly increasing number of vehicles in cities is a significant source of air pollution. Vehicles release various pollutants into the atmosphere:

• Carbon Monoxide: A poisonous gas produced by the incomplete burning of fuels like petrol and diesel. It reduces the oxygen-carrying capacity of the blood.
• Carbon Dioxide: A greenhouse gas.
• Nitrogen Oxides: Contribute to smog and acid rain.
• Smoke: Contains tiny particles that can cause respiratory problems.

During winters, cities often experience a thick, fog-like layer called smog. Smog is a mixture of smoke and fog. It can contain oxides of nitrogen and other air pollutants. Smog causes breathing difficulties, such as asthma, coughing, and wheezing, particularly in children.

Many industries release pollutants. Petroleum refineries, for instance, are major sources of gaseous pollutants like sulphur dioxide and nitrogen dioxide. Sulphur dioxide is also produced from burning fuels like coal in power plants. It can cause respiratory problems and permanent lung damage.

Other air pollutants include chlorofluorocarbons (CFCs), which were commonly used in refrigerators, air conditioners, and aerosol sprays. CFCs damage the ozone layer in the atmosphere, which protects us from the sun's harmful ultraviolet rays. Although the use of CFCs is being phased out and less harmful alternatives are being used, their long lifespan means they continue to impact the ozone layer.

Automobiles, especially those burning diesel and petrol, also release tiny particulate matter into the air. These fine particles remain suspended for long periods, reducing visibility and causing respiratory diseases when inhaled. Similar particles are produced by industries like steel making, mining, and power plants (releasing ash particles).

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Case Study— The Taj Mahal

The beauty of the Taj Mahal, a monument made of white marble located in Agra, is being threatened by air pollution. Air pollutants affect not only living organisms but also non-living structures like buildings and statues.

Industries in and around Agra, including rubber processing, automobile, chemical plants, and particularly the Mathura oil refinery, release pollutants like sulphur dioxide and nitrogen dioxide. These gases react with water vapour in the atmosphere to form sulphuric acid and nitric acid. When it rains, these acids fall to the ground, resulting in acid rain.

Acid rain corrodes the marble of the Taj Mahal, causing damage to the monument. This damage to marble by acid rain is sometimes referred to as "Marble cancer". Suspended particulate matter, such as soot emitted by the Mathura oil refinery, also contributes to the yellowing of the white marble.

To protect the Taj Mahal, the Supreme Court of India has mandated measures such as industries in the Taj zone switching to cleaner fuels like Compressed Natural Gas (CNG) and Liquefied Petroleum Gas (LPG), and automobiles using unleaded petrol.

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Greenhouse Effect

The Earth's atmosphere traps some of the Sun's heat, which is essential for life. This process is called the greenhouse effect, named after greenhouses which trap solar heat. Solar radiation reaches the Earth's surface, some is absorbed, and some is reflected back. A portion of the reflected radiation is absorbed and trapped by certain gases in the atmosphere, warming the Earth.

While the greenhouse effect is natural and necessary to maintain a habitable temperature on Earth, an increase in the concentration of certain gases in the atmosphere intensifies this effect, leading to a gradual rise in the Earth's average temperature. These gases are called greenhouse gases. The primary greenhouse gas is carbon dioxide ($\text{CO}_2$). Other greenhouse gases include methane ($\text{CH}_4$), nitrous oxide ($\text{N}_2\text{O}$), and water vapour.

The level of $\text{CO}_2$ in the atmosphere is increasing primarily due to human activities. Burning fossil fuels (coal, petroleum, natural gas) for energy and transportation releases large amounts of $\text{CO}_2$. Simultaneously, deforestation reduces the number of trees, which consume $\text{CO}_2$ during photosynthesis. This combination leads to an accumulation of $\text{CO}_2$ in the atmosphere.

The increased concentration of greenhouse gases trapping excess heat causes a gradual rise in the average temperature of the Earth's atmosphere, a phenomenon known as global warming.

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Global Warming

Global warming is a serious global issue. Even small increases in average temperature (e.g., $0.5^\circ\text{C}$) can have significant impacts. Potential consequences of global warming include:

• Melting of glaciers and ice caps, leading to a dramatic rise in sea levels and flooding of coastal areas.
• Changes in global rainfall patterns, affecting agriculture.
• Adverse impacts on forests, plant life, and animal species, potentially leading to habitat loss and extinction.

Many countries recognise the threat of global warming and have entered into international agreements, such as the Kyoto Protocol, to reduce the emission of greenhouse gases. Scientific reports indicate a limited time frame to act before the temperature rise reaches dangerous levels.

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What Can Be Done?

Combating air pollution requires collective effort. There are many successful examples of reducing air pollution through proactive measures.

One key strategy is to switch to cleaner fuels. For example, Delhi significantly reduced its air pollution levels by mandating the use of Compressed Natural Gas (CNG) and unleaded petrol in vehicles instead of diesel and leaded petrol.

Individual actions also contribute. We can choose environment-friendly modes of transport like walking, cycling, or using public transport instead of individual cars. Planting trees and taking care of existing ones helps reduce $\text{CO}_2$ levels (as trees absorb $\text{CO}_2$) and improves air quality. Events like Van Mahotsav involve large-scale tree planting. Awareness campaigns, such as discouraging the bursting of firecrackers during festivals, can also help reduce pollution.

Instead of burning dry leaves and other organic waste, which releases smoke and pollutants, composting is a better option that converts waste into useful manure.

Regular monitoring of air quality by government agencies and increasing public awareness about air pollution are also important steps.

Ultimately, reducing air pollution requires a shift away from fossil fuels towards alternative energy sources like solar energy, hydropower, and wind energy.

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Water Pollution

Water is an indispensable and precious resource, but it is becoming increasingly scarce due to growing population, industrialization, and agricultural activities. Water pollution occurs when harmful substances get mixed with water, spoiling its quality and making it unfit for use.

The substances that pollute water are called water pollutants. Using water for activities like washing clothes or bathing adds pollutants to it, changing its smell, colour, and overall quality.

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How Does Water Get Polluted?

Water bodies are contaminated by various sources of pollution:

• Sewage: Untreated or partially treated sewage from homes and other buildings is often discharged directly into rivers and lakes. Sewage contains food waste, detergents, microorganisms, and other harmful substances. It pollutes water and can contaminate groundwater by seeping into the soil.
• Industrial Waste: Many industries, such as oil refineries, paper factories, textile and sugar mills, and chemical factories, discharge toxic chemicals and other harmful waste directly into rivers and streams. These industrial effluents contain dangerous chemicals like arsenic, lead, and fluorides, which can be toxic to plants and animals and cause chemical contamination of water. Regulations exist requiring industries to treat their waste before disposal, but these are often not followed. Polluted water can also harm soil quality.
• Agricultural Chemicals: Pesticides and weedicides used in farming to protect crops dissolve in water. Rainwater washes these chemicals into nearby water bodies, polluting them. They can also seep into the ground and contaminate groundwater.
• Excess Nutrients: Agricultural runoff containing fertilisers can lead to excessive quantities of nutrients (like nitrates and phosphates) entering water bodies. These nutrients promote the rapid growth of algae (algal blooms), which cover the water surface and block sunlight. When the algae die, decomposer bacteria multiply rapidly, consuming a large amount of dissolved oxygen in the water. The resulting lack of oxygen harms or kills aquatic organisms like fish.
• Hot Water: Hot water discharged from power plants and industries into rivers can also be a pollutant. It raises the temperature of the water body, negatively affecting the aquatic ecosystem.

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Case Study Ganga

The river Ganga is a lifeline for millions in northern, central, and eastern India. However, it is one of the world's most endangered rivers due to severe pollution. Over the years, pollution levels have drastically increased as towns and cities along its course discharge large quantities of garbage, untreated sewage, and industrial waste directly into the river. At certain points, pollution is so high that the river is considered 'dead', unable to support aquatic life.

An initiative called the Ganga Action Plan was launched in 1985 to reduce pollution, but its success was limited due to increasing population and industrialization. The Government of India launched a new initiative, the National Mission for Clean Ganga (NMCG), in 2016.

Kanpur, a heavily populated city in Uttar Pradesh, is a particularly polluted stretch of the Ganga. The river's flow is slow, and the water volume is relatively small. Thousands of industries, including fertiliser, detergent, leather, and paint factories, discharge untreated toxic chemical waste into the river. Additionally, people contribute by bathing, washing clothes, defecating, and dumping garbage and waste materials directly into the river.

Water contaminated with sewage can contain harmful microorganisms like bacteria, viruses, fungi, and parasites, causing diseases such as cholera, typhoid, and jaundice. The presence of bacteria found in mammal faeces is an indicator of fecal contamination and poor water quality.

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What Is Potable Water And How Is Water Purified?

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What Is Potable Water?

Potable water is water that is safe and suitable for drinking. Even water that appears clear and odorless may contain disease-causing microorganisms or dissolved impurities, making purification necessary.

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How Is Water Purified?

Water is treated to make it safe for drinking. Municipal bodies treat water before supplying it to households. Sewage treatment plants clean wastewater before releasing it into water bodies.

Household methods to purify water include:

• Filtering: This is a physical process to remove suspended impurities. Candle-type water filters are commonly used in households. A simple filter can be made with layers of cloth/paper napkin, cotton, sand, and gravel.
• Boiling: Heating water to its boiling point kills most germs (microorganisms) present in it, making it safe to drink.
• Chlorination: A chemical method involving adding chlorine tablets or bleaching powder to water. Chlorine kills germs. It's important to use the correct amount as specified.

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What Can Be Done?

Reducing water pollution requires efforts at both the industrial and individual levels. Laws mandating that industrial units treat their waste before discharging it into water bodies must be strictly enforced. Water treatment plants should be installed in all industrial areas.

Individually, we can significantly contribute by consciously conserving water and avoiding wastage. Adopting the principle of Reduce, Reuse, and Recycle is crucial.

Creative ways to reuse water include using water from washing vegetables to water plants in the garden. Simple habits like turning off taps while brushing teeth can save litres of water. Even a dripping tap can waste thousands of litres annually.

Pollution is a pressing issue affecting daily life and the planet's survival. It is everyone's responsibility to adopt environment-friendly practices to ensure a healthier future.

Globally, a significant portion of the population lacks access to safe drinking water, highlighting the urgency of addressing water quality and availability.

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