Pollution, Climate Change and Ozone

Air looks clean when it is not. Air pollution means the presence in the atmosphere of substances, in such quantity and for such time, that they harm humans, other living things or property. Some pollutants are natural (volcanic ash, dust storms, forest fires, pollen) but today the big ones are man-made: burning coal and oil, vehicles, industries, burning of crop stubble and garbage, construction dust and cooking on wood or dung. The first thing to learn is to separate primary pollutants, which are released directly, from secondary pollutants, which are formed in the air by reactions between primary ones.

Why is PM2.5 more dangerous than PM10? Size decides depth. Larger PM10 particles are mostly trapped by the hairs and mucus of the nose and throat. The much smaller PM2.5 slips past these defences, travels deep into the lungs (the alveoli) and can even enter the bloodstream. For a feel of the scale, a human hair is about 50 to 70 micrometres wide, so PM2.5 is roughly 20 to 30 times thinner.

To tell a citizen in one glance how bad the air is, India launched the National Air Quality Index (AQI) on 17 October 2014 under the Swachh Bharat campaign. Its slogan is 'One Number, One Colour, One Description'. The Central Pollution Control Board (CPCB) releases it. The AQI uses eight pollutants: PM10, PM2.5, NO2, SO2, CO, O3, NH3 and Pb. For each pollutant a sub-index is worked out, and the final AQI is the highest of these sub-indices (the worst pollutant decides, it is not an average). The AQI needs data of at least three pollutants, and one of them must be PM2.5 or PM10. PM10, PM2.5, NO2, SO2, NH3 and Pb use a 24-hour average, while CO and O3 use an 8-hour average.

India's legal tools come in a clear order. The Air (Prevention and Control of Pollution) Act, 1981 is the main law for air; it empowers the CPCB and State Pollution Control Boards to set standards and declare air pollution control areas. The Environment (Protection) Act, 1986, passed after the Bhopal gas tragedy, is the umbrella law that covers everything. The National Ambient Air Quality Standards (NAAQS) of 2009 set the limits: for example, 40 micrograms per cubic metre as annual average for PM2.5 and 60 for PM10, while the World Health Organization's 2021 guideline is much stricter at 5 micrograms for annual PM2.5. In 2019, the National Clean Air Programme set a goal of cutting PM2.5 and PM10 by 20 to 30 per cent by 2024 (over 2017 levels) in over a hundred cities that fail the standards. In Delhi-NCR, the Commission for Air Quality Management (CAQM) and the Graded Response Action Plan (GRAP) act in steps as the AQI worsens.

Water, soil and waste pollution are all about one idea: something that does not belong is added faster than nature can clean it up. A river can absorb a little sewage and still run clean. Pour in too much and the oxygen runs out, fish die and the water turns dangerous to drink. In this topic you learn the indicators (BOD, DO, coliform), the famous poisonings, the laws and the way India manages its waste.

BOD and DO move in opposite directions. When sewage enters a river, microbes multiply to eat it and use up the oxygen, so BOD rises and DO falls. Remember it as: dirty water, high BOD, low DO.

Without any greenhouse effect Earth would average about minus 18 degrees Celsius, a frozen planet. Because gases in the air trap heat, the real average is near 15 degrees. So the greenhouse effect is a friend. The trouble begins when humans add far more of these gases, burning fossil fuels and clearing forests, and the blanket gets thicker. Global warming is that extra, human-made warming. This topic explains the gases, the science and the impacts, with the India-specific examples the exam loves.

GWP (global warming potential) compares how much heat a gas traps with CO2 over a period, usually 100 years. CO2 is the baseline with GWP 1. Methane is less in quantity and shorter-lived but much stronger per tonne, which is why paddy fields and cattle matter for climate.

Ozone is a strange gas: the same molecule is a shield in the sky and a poison on the ground. High up in the stratosphere it absorbs harmful ultraviolet rays and protects life. Near the ground it burns lungs and crops. This topic separates the two, tells the story of how CFCs punched a hole in the shield and how the world fixed it, and then covers the other two air problems that come from the same fuels: acid rain and smog.

Acid rain is rain, snow, fog or dust that is more acidic than normal. Clean rain is itself slightly acidic, with a pH of about 5.6, because carbon dioxide dissolves in it. Rain below pH 5.6 is called acid rain. It forms when sulphur dioxide (from burning coal and from smelters) and nitrogen oxides (from vehicles and power plants) turn into sulphuric and nitric acid in the air.

Pollution and warming do not stop at borders, so countries have had to learn to bargain. The story runs in a straight line: Stockholm (1972) put the environment on the world agenda, Rio (1992) created the climate treaty, Kyoto (1997) gave binding targets to rich countries, and Paris (2015) asked every country to make its own promise. The one idea that runs through all of it is fairness: who caused the problem, who can afford to fix it?

CBDR-RC means Common But Differentiated Responsibilities and Respective Capabilities. Every country must protect the climate (common), but rich countries caused most past emissions and have more money and technology, so they must lead on cuts and on climate finance (differentiated). It comes from Principle 7 of the Rio Declaration and Article 3 of the UNFCCC.

CCPI scores countries on four categories: GHG emissions (40 per cent), renewable energy (20), energy use (20) and climate policy (20). Remember 4-2-2-2. In its ranking the top three places are left empty because no country is performing well enough to deserve them.

India is the third-largest emitter in total, yet its emissions per person are far below the world average, and its people are still lifting themselves out of poverty. That is why India's stand is always the same: climate action must be fair, and rich countries must lead and pay. At the same time India has set big targets of its own. This topic lists them in a clean order: the NDCs, the Glasgow Panchamrit, the NAPCC missions, and the newer tools such as LiFE, carbon markets, green hydrogen and the International Solar Alliance.

At COP26 in Glasgow (1 November 2021) the Prime Minister announced five commitments called the Panchamrit, the five nectars of climate action.