# Air Pollution for UPSC: Pollutants, AQI, NAAQS, WHO Guidelines, NCAP (130 Cities), CAQM and GRAP Source: https://tracknation.in/story/air-pollution-for-upsc-pollutants-aqi-naaqs-who-guidelines-ncap-130-cities-caqm-and-grap (TrackNation — free UPSC notes with PYQs) > Air pollution for UPSC: pollutants and sources (SO2, NOx, PM2.5, ozone, benzene, crop-residue burning), acid rain and photochemical smog, the AQI and WHO 2021 guidelines, the National Clean Air Programme (130 cities, 40 per cent PM10 target, 2025 results), CAQM and GRAP. Includes practice questions, the real PYQs and exact Mains questions. ## How UPSC Tests Air Pollution 🎯 **Exam priority: Tier-2. Air questions are cause-and-effect questions: which pollutant comes from which source and which is regulated how.** *UPSC asked: which gases the Air Quality Index counts (2016); what is released when crop residue burns (2019: CO, methane, ozone, SO2); benzene exposure sources (2020); copper smelting, furnace oil and magnetite particles (2021); the WHO Air Quality Guidelines for PM2.5 and ozone (2022); which gases cause acid rain (2022); the largest source of sulphur dioxide (2024: power plants burning fossil fuels); and artificial rain with silver iodide for air pollution (2025). Mains asked the WHO guidelines and the National Clean Air Programme (2021) and photochemical smog with the Gothenburg Protocol (2022).* Use a three-box memory: **what the pollutant is** (primary, secondary), **where it comes from** and **how it is measured and controlled**. ## Pollutants, Sources, Acid Rain and Photochemical Smog ## The pollutants and their sources | **Pollutant** | **Main sources** | **Effect** | | PM10 and PM2.5 (particulate matter) | Road and construction dust, vehicles, open burning, industry, crop-residue burning | Lung damage; PM2.5 is fine enough to enter the bloodstream (2022 PYQ) | | Sulphur dioxide (SO2) | Burning of coal and oil: power plants are the largest source (2024 PYQ); metal smelting (copper, 2021 PYQ); high-sulphur furnace oil (2021 PYQ) | Acid rain; respiratory harm | | Nitrogen oxides (NOx) | Vehicles and power plants | Acid rain and ozone formation | | Carbon monoxide (CO) | Incomplete combustion: vehicles, biomass burning | Reduces oxygen carrying capacity of blood | | Ground-level (tropospheric) ozone | Formed in sunlight from NOx and volatile organic compounds (a secondary pollutant) | Peaks in sunny weather, not in bad weather; triggers asthma (2022 PYQ) | | Benzene and volatile organic compounds | Vehicle exhaust, tobacco smoke, wood burning; some solvents | Carcinogenic (2020 PYQ) | | Ammonia, lead | Agriculture, industry | Included in the AQI | **Crop-residue burning** releases carbon monoxide, methane, ozone precursors and sulphur dioxide, together with fine particles and smog that settle over northern India in winter (2019 PYQ). **Brakes, engines and power plants** are the sources of magnetite particles (2021 PYQ). ### Acid rain Sulphur dioxide and nitrogen oxides dissolve in cloud water as sulphuric and nitric acid and fall as acid rain; carbon monoxide and ozone are not the cause (2022 PYQ). It damages forests, soils, lakes and marble monuments. ### Photochemical smog (Mains 2022) In strong sunlight, nitrogen oxides react with volatile organic compounds to form ozone and other oxidants (the *photochemical smog* of cities such as Los Angeles and Delhi in summer). It irritates eyes and lungs and damages crops. The 1999 **Gothenburg Protocol** (under the UNECE air-pollution convention) sets national ceilings for sulphur, nitrogen oxides, ammonia and volatile organic compounds to reduce acidification, eutrophication and ground-level ozone. ## AQI, Standards, NCAP, CAQM and GRAP ## Measuring air: AQI, NAAQS and the WHO guidelines - **National Air Quality Index (AQI):** six categories: Good, Satisfactory, Moderately Polluted, Poor, Very Poor and Severe. It combines up to eight pollutants (PM10, PM2.5, NO2, SO2, CO, O3, NH3 and lead). Carbon dioxide and methane are greenhouse gases, not AQI pollutants (2016 PYQ). - **NAAQS (National Ambient Air Quality Standards):** the legal limits India sets for each pollutant. The Ministry's NCAP target uses the PM10 limit of **60 µg/m³** (annual average). - **WHO Global Air Quality Guidelines (2021):** tightened the 2005 values: for PM2.5 the annual guideline is **5 µg/m³** and the 24-hour guideline **15 µg/m³** (2022 PYQ statement 1 was correct). WHO guidelines are advisory, and Indian standards are higher. ## India's response: NCAP and the regulators - **National Clean Air Programme (NCAP):** covers **130 cities** in 24 States and Union Territories (82 non-attainment cities, 40 more non-attainment and million-plus cities and 8 million-plus cities). It aims to cut PM10 by up to **40 per cent against the 2019-20 baseline** or bring cities to the PM10 standard of 60 µg/m³ by **2025-26**. Each city has a Clean Air Action Plan with annual PM10 targets, tracked on the **PRANA portal**; air quality is monitored at **855 stations** (500 manual and 355 continuous stations). - **Results (PIB year-end review, 31 December 2025):** 103 cities reduced PM10 in 2024-25 compared with 2017-18; 64 of them by more than 20 per cent and 25 by more than 40 per cent; 22 cities met the PM10 standard. Performance-linked funding of ₹13,415 crore has been provided. - **Swachh Vayu Survekshan:** ranks cities on action plan implementation; best performers are felicitated on National Swachh Vayu Diwas (7 September); ward-level guidelines were released in September 2025. - **Commission for Air Quality Management (CAQM):** a statutory body for the National Capital Region and adjoining areas (CAQM Act, 2021) that runs the **Graded Response Action Plan (GRAP)** of winter-time emergency measures; the GRAP schedule was revised in September and December 2024. - **Air (Prevention and Control of Pollution) Act, 1981:** industries in air-pollution control areas need *consent* from the State Boards, which can prescribe emission standards after consulting the Central Board. - **Cloud seeding:** artificial rain to clear pollution uses silver iodide (and some mixes include potassium iodide); it is a topical emergency idea, not a control measure (2025 PYQ). ## How UPSC Could Ask This Next ## How UPSC Could Ask This Next - **Source-and-pollutant matching:** which gas comes from burning crop residue, smelting or furnace oil, and which is the largest source of SO2. - **Standards:** which pollutants are in the AQI, the WHO's PM2.5 and ozone statements, the NCAP's PM10 target. - **Programmes:** the number of NCAP cities, the 40 per cent target and the 2025-26 deadline, CAQM and GRAP, Swachh Vayu Survekshan. - **Secondary pollutants:** ozone and smog formation, and acid rain's causes. ## Further Reading - NCERT Biology (Class 12) and Geography textbooks, the India State of Forest Report, the MoEFCC Annual Report, the Economic Survey and the official lists cited in this note — the primary sources behind every figure above. ## Test Yourself: Practice Questions and PYQs Twelve practice questions on air pollutants, standards and India's clean-air programmes, followed by the real UPSC Prelims questions and exact Mains questions. ## Practice Questions **Q1.** The National Clean Air Programme (NCAP) aims to reduce PM10 concentrations by up to what share against the 2019-20 baseline, or to bring cities to the PM10 standard, by 2025-26? - (a) 10 per cent - (b) 20 per cent - (c) 40 per cent - (d) 60 per cent **Answer: (c)** — NCAP's target is up to 40 per cent, or meeting the 60 µg/m³ PM10 standard. **Q2.** How many cities are covered under the National Clean Air Programme? - (a) 130 - (b) 200 - (c) 90 - (d) 102 **Answer: (a)** — 130 cities in 24 States and UTs: 82 non-attainment, 40 non-attainment plus million-plus and 8 million-plus cities. **Q3.** Consider the following statements about the NCAP's performance as reported by the PIB (December 2025): 1. 103 cities recorded a reduction in PM10 in 2024-25 compared with 2017-18. 2. 64 of them showed a reduction of more than 20 per cent. 3. 22 cities met the National Ambient Air Quality Standards for PM10. Which of the statements given above are correct? - (a) 1 and 2 only - (b) 1, 2 and 3 - (c) 2 and 3 only - (d) 1 and 3 only **Answer: (b)** — All three figures are in the review. **Q4.** In the context of the National Air Quality Index in Indian cities, which of the following gases are considered? 1. Carbon dioxide 2. Carbon monoxide 3. Nitrogen dioxide 4. Sulphur dioxide 5. Methane - (a) 2, 3 and 4 only - (b) 1, 4 and 5 only - (c) 1, 2, 3, 4 and 5 - (d) 1, 2 and 3 only **Answer: (a)** — CO, NO2 and SO2 are AQI pollutants; CO2 and methane are not. **Q5.** Which of the following is released into the atmosphere on burning crop or biomass residue? 1. Carbon monoxide 2. Methane 3. Ozone (precursors) 4. Sulphur dioxide - (a) 1, 2, 3 and 4 - (b) 2, 3 and 4 only - (c) 1 and 2 only - (d) 1 and 4 only **Answer: (a)** — All four are released. **Q6.** Acid rain is caused by excess of - (a) carbon dioxide and methane - (b) CFCs - (c) sulphur dioxide and oxides of nitrogen - (d) carbon monoxide and ozone **Answer: (c)** — The two form sulphuric and nitric acids in the atmosphere. **Q7.** Which of the following is the largest source of sulphur dioxide emissions? - (a) Volcanoes - (b) Locomotives - (c) Ships - (d) Burning fossil fuels in power plants **Answer: (d)** — UPSC's 2024 key: power plants burning fossil fuels. **Q8.** Consider the following statements about WHO's 2021 Air Quality Guidelines: 1. The annual mean of PM2.5 should not exceed 5 µg/m³. 2. The highest levels of ground-level ozone occur during bad weather. 3. PM10 is the fraction that enters the bloodstream. Which of the statements given above is/are correct? - (a) 1, 2 and 3 - (b) 1 only - (c) 2 and 3 - (d) 1 and 2 **Answer: (b)** — Ozone peaks in sunny weather and PM2.5 (not PM10) enters the bloodstream. **Q9.** Which body administers the Graded Response Action Plan (GRAP) for the National Capital Region? - (a) National Green Tribunal - (b) Bureau of Indian Standards - (c) National Biodiversity Authority - (d) Commission for Air Quality Management (CAQM) **Answer: (d)** — CAQM was set up under the 2021 Act. **Q10.** Artificial rain to reduce air pollution typically uses - (a) calcium carbonate - (b) silver nitrate and potassium chloride - (c) sodium chloride only - (d) silver iodide and potassium iodide **Answer: (d)** — Cloud seeding agents include silver iodide and potassium iodide. **Q11.** Which one of the following is a secondary pollutant formed in sunlight from nitrogen oxides and volatile organic compounds? - (a) Particulate matter from road dust - (b) Lead - (c) Ground-level ozone - (d) Carbon monoxide **Answer: (c)** — Ozone is not emitted directly; it forms in the atmosphere. **Q12.** Under the Air (Prevention and Control of Pollution) Act, 1981, industries operating in air-pollution control areas must obtain - (a) approval from the Supreme Court - (b) consent from the State Pollution Control Board - (c) a permit from the National Green Tribunal - (d) a licence from the Ministry of Commerce **Answer: (b)** — The consent mechanism is the Act's core regulatory tool. ### UPSC Previous Year Questions (PYQs) *Real UPSC Prelims questions, checked against the official paper and answer key.* **Q1.** (2016) In the cities of our country, which among the following atmospheric gases are normally considered in calculating the value of Air Quality Index? 1. Carbon dioxide 2. Carbon monoxide 3. Nitrogen dioxide 4. Sulfur dioxide 5. Methane Select the correct answer using the code given below. - (a) 1, 2 and 3 only - (b) 2, 3 and 4 only - (c) 1, 4 and 5 only - (d) 1, 2, 3, 4 and 5 **Answer: (b)** — Among the gases listed, the AQI counts carbon monoxide, nitrogen dioxide and sulphur dioxide. Carbon dioxide and methane are greenhouse gases but are not AQI pollutants. **Q2.** (2019) Consider the following: 1. Carbon monoxide 2. Methane 3. Ozone 4. Sulphur dioxide Which of the above are released into atmosphere due to the burning of crop/biomass residue? - (a) 2, 3 and 4 only - (b) 1 and 2 only - (c) 1, 2, 3 and 4 - (d) 1 and 4 only **Answer: (c)** — Burning crop residue releases carbon monoxide, methane, ozone precursors and sulphur dioxide, so all four are released. **Q3.** (2020) Which of the following are the reasons/factors for exposure to benzene pollution? 1. Automobile exhaust 2. Tobacco smoke 3. Wood burning 4. Using varnished wooden furniture 5. Using products made of polyurethane Select the correct answer using the code given below: - (a) 1, 2, 3, 4 and 5 - (b) 2 and 4 only - (c) 1, 3 and 4 only - (d) 1, 2 and 3 only **Answer: (d)** — UPSC's key counts vehicle exhaust, tobacco smoke and wood burning as the sources of benzene exposure (1, 2 and 3); finished varnish and polyurethane products release little once cured. **Q4.** (2022) In the context of WHO Air Quality Guidelines, consider the following statements : 1. The 24-hour mean of PM 2.5 should not exceed 15 µg/m3 and annual mean of PM2.5 should not exceed 5 µg/m3. 2. In a year, the highest levels of ozone pollution occur during the periods of inclement weather. 3. PM10 can penetrate the lung barrier and enter the bloodstream. 4. Excessive ozone in the air can trigger asthma. Which of the statements given above are correct ? - (a) 1, 3 and 4 - (b) 2, 3 and 4 - (c) 1 and 4 only - (d) 1 and 2 only **Answer: (c)** — WHO's 2021 guideline for PM2.5 is 15 µg/m³ for 24 hours and 5 µg/m³ for the year (1 is right). Ozone peaks in sunny weather, not bad weather (2 is wrong), PM2.5 (not PM10) is the fraction that enters the bloodstream (3 is wrong) and ozone can trigger asthma (4 is right). **Q5.** (2022) Consider the following: 1. Carbon monoxide 2. Nitrogen oxide 3. Ozone 4. Sulphur dioxide Excess of which of the above in the environment is/are cause(s) of acid rain? - (a) 1, 2 and 3 - (b) 4 only - (c) 1, 3 and 4 - (d) 2 and 4 only **Answer: (d)** — Sulphur dioxide and nitrogen oxides form sulphuric and nitric acid in the air, which cause acid rain. Carbon monoxide and ozone are not the cause. **Q6.** (2024) According to the Environmental Protection Agency (EPA), which one of the following is the largest source of sulphur dioxide emissions ? - (a) Locomotives using fossil fuels - (b) Extraction of metals from ores - (c) Ships using fossil fuels - (d) Power plants using fossil fuels **Answer: (d)** — Burning fossil fuels in power plants is the largest source of sulphur dioxide emissions. **Q7.** (2021) Why is there a concern about copper smelting plants? 1. They may release lethal quantities of carbon monoxide into environment. 2. The copper slag can cause the leaching of some heavy metals into environment. 3. They may release sulphur dioxide as a pollutant. Select the correct answer using the code given below. - (a) 1, 2 and 3 - (b) 1 and 2 only - (c) 2 and 3 only - (d) 1 and 3 only **Answer: (c)** — Copper smelting releases sulphur dioxide, and the slag can leach heavy metals. It does not emit lethal quantities of carbon monoxide, so 2 and 3. **Q8.** (2021) With reference to furnace oil, consider the following statements: 1. It is a product of oil refineries. 2. Some industries use it to generate power. 3. Its use causes sulphur emissions into environment. Which of the statements given above are correct? - (a) 1, 2 and 3 - (b) 1 and 2 only - (c) 2 and 3 only - (d) 1 and 3 only **Answer: (a)** — Furnace oil is a refinery product, some industries use it to generate power, and its sulphur content leads to sulphur emissions, so all three are correct. **Q9.** (2021) Magnetite particles, suspected to cause neurodegenerative problems, are generated as environmental pollutants from which of the following? 1. Brakes of motor vehicles 2. Engines of motor vehicles 3. Microwave stoves within homes 4. Power plants 5. Telephone lines Select the correct answer using the code given below. - (a) 1, 2, 3 and 5 only - (b) 3, 4 and 5 only - (c) 1, 2 and 4 only - (d) 1, 2, 3, 4 and 5 **Answer: (c)** — Magnetite particles come from vehicle brakes and engines and power plants; microwave ovens and telephone lines are not sources. **Q10.** (2025) Artificial way of causing rainfall to reduce air pollution makes use of - (a) silver nitrate and potassium iodide - (b) silver iodide and potassium iodide - (c) silver nitrate and potassium chloride - (d) silver iodide and potassium nitrate **Answer: (b)** — Cloud seeding for artificial rain uses silver iodide, and mixes may add potassium iodide. ### Mains Practice Questions Use these to frame full-length answers. You don't have to answer one exactly — they show the angles UPSC tests, so let them guide which points you cover. - Describe the key points of the revised Global Air Quality Guidelines of the WHO. How are they different from the 2005 update? What changes in India's National Clean Air Programme are required to achieve them? - Discuss in detail photochemical smog, its formation, effects and mitigation. Explain the 1999 Gothenburg Protocol. - Examine the effectiveness of the National Clean Air Programme using the 2025 outcomes. What explains the gap between the cities that met the standards and the rest? - Stubble burning, vehicle emissions and construction dust are the major contributors to winter air pollution in north India. Suggest an integrated response. - How do GRAP and the CAQM address episodic air pollution in the National Capital Region? Evaluate their limits. ### UPSC Mains — Previous Years’ Questions on this topic (last 10 years) These are the **actual GS Mains questions** UPSC has asked on this theme — real proof of how, and when, it is tested. Try to write a full answer to each. - 2022 (GS-III): Discuss in detail the photochemical smog emphasizing its formation, effects and mitigation. Explain the 1999 Gothenburg Protocol. - 2021 (GS-III): Describe the key points of the revised Global Air Quality Guidelines (AQGs) recently released by the World Health Organisation (WHO). How are these different from its last update in 2005 ? What changes in India's National Clean Air Programme are required to achieve these revised standards?