Prelims · Environment & ecology · 40 questions

Pollution & waste

Every UPSC Prelims question on this topic, 2016–2026, newest first. Tap an option to check yourself; the answer and explanation open below it.

Asked in 10 of 11 years · most in 2021 (6)

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Prelims 2022 · Q44

Medium

In the context of WHO Air Quality Guidelines, consider the following statements:

1.The 24-hour mean of PM2.5 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?

Answer & explanation

Answer: (b) 1 and 4 only

Statements 1 and 4 are correct. WHO's 2021 guidelines set PM2.5 at 5 µg/m3 a year and 15 µg/m3 over 24 hours, and ozone can trigger asthma. Ozone peaks in hot, sunny weather, not bad weather, and it is PM2.5, not PM10, that WHO says can enter the bloodstream.

✓ 1. The WHO Air Quality Guidelines (2021) recommend an annual average of 5 µg/m3 and a 24-hour average of 15 µg/m3 for PM2.5.
✗ 2. Ground-level ozone forms when pollutants react in sunlight, so it is most likely to reach unhealthy levels on hot sunny days, not in inclement weather.
✗ 3. Both PM2.5 and PM10 can go deep into the lungs, but WHO says only the finer PM2.5 can even enter the bloodstream.
✓ 4. Ozone irritates and inflames the airways, aggravates asthma and increases the frequency of asthma attacks.

Remember · WHO 2021: PM2.5 annual 5, 24-hour 15 µg/m3 (PM10: 15 and 45). Ozone peaks on hot sunny days and worsens asthma. Only PM2.5 reaches the blood.

Sources

WHO, Billions of people still breathe unhealthy air: new WHO data, 4 April 2022 (Internet Archive copy) ↗ “The latest WHO Air Quality Guidelines (2021) recommend the following concentration limits for these pollutants: For PM 2.5 : Annual average 5 µg/m 3 ; 24-hour average 15 µg/m 3”
WHO, WHO global air quality guidelines: questions and answers (Internet Archive copy) ↗ “PM₂.₅ and PM₁₀ are capable of penetrating deep into the lungs and PM₂.₅ can even enter the bloodstream, primarily resulting in cardiovascular and respiratory impacts.”
US EPA, Ground-level Ozone Basics (Internet Archive copy) ↗ “Ozone is most likely to reach unhealthy levels on hot sunny days in urban environments, but can still reach high levels during colder months.”
US EPA, Health Effects of Ozone Pollution (Internet Archive copy) ↗ “Aggravate lung diseases such as asthma, emphysema, and chronic bronchitis. Increase the frequency of asthma attacks.”

Question and answer: UPSC's official GS Paper I (2022, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink ·

Prelims 2022 · Q46

Medium

With reference to polyethylene terephthalate, the use of which is so widespread in our daily lives, consider the following statements:

1.Its fibres can be blended with wool and cotton fibres to reinforce their properties.
2.Containers made of it can be used to store any alcoholic beverage.
3.Bottles made of it can be recycled into other products.
4.Articles made of it can be easily disposed of by incineration without causing greenhouse gas emissions.

Which of the statements given above are correct?

Answer & explanation

Answer: (a) 1 and 3

Statements 1 and 3 are correct: PET is the polyester of clothing, blended with cotton and wool, and PET bottles are recycled, mostly into polyester fibre. Statement 2 is wrong because PET lets in oxygen and is unsuited to long storage of some alcoholic drinks. Statement 4 is wrong because burning PET turns its carbon into carbon dioxide, a greenhouse gas.

✓ 1. PET fibres are used alone or blended with natural fibres such as cotton, and wool-polyester and cotton-polyester blends are common textile mixes.
✗ 2. PET has only moderate oxygen permeability, so it suits short storage but harms the aroma of an alcoholic drink such as wine when kept for long. It is not fit for any and every alcoholic beverage.
✓ 3. PET bottles are mechanically recycled; in India most recycled PET, about 95% by one estimate, is spun into polyester fibre.
✗ 4. Burning plastic releases CO2 in proportion to its carbon. EPA's model takes PET as 63% carbon, with about 98% of that carbon turning into CO2 on combustion.

Remember · PET = polyester: blended with cotton and wool, and recycled (mostly into fibre). Burning it releases CO2, and it is a poor container for long-stored alcoholic drinks.

Sources

NIH National Library of Medicine (PMC), Recycling Textiles: From Post-Consumer Polyester Garments to Materials for Injection Molding ↗ “In textile products, PET fibers are often used alone or blended with natural fibers such as cotton to improve breathability, or with elastane to create stretch fabrics.”
NIH National Library of Medicine (PMC), Depolymerization of Polycotton-Blended Fabrics: Challenges and Opportunities ↗ “blended materials, like cotton–polyester, wool–polyester, cotton–wool, or wool–cotton–polyester”
NIH National Library of Medicine (PMC), Roadmap to sustainable plastic waste management: recycling PET in Singapore and India ↗ “In India and Singapore, mechanically recycled PET materials were utilized to make polyester fibres.”
NIH National Library of Medicine (PubMed), Aromatic evolution of wine packed in virgin and recycled PET bottles (Internet Archive copy) ↗ “Because of their moderate oxygen permeability, the use of virgin PET and recycled PET bottles could be adapted for short conservation of wine but detrimental to aromatic quality if long conservation is intended.”
US EPA, WARM model: Plastics (greenhouse-gas emission factors) ↗ “CO2 emissions from combusting plastic depend on the carbon content of the plastic and the amount of carbon that is converted to CO2 during the combustion process.”

Question and answer: UPSC's official GS Paper I (2022, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 1 Oct 2026 (how we verify). Permalink ·

Prelims 2022 · Q98

Medium

Consider the following statements:

1.Other than those made by humans, nanoparticles do not exist in nature.
2.Nanoparticles of some metallic oxides are used in the manufacture of some cosmetics.
3.Nanoparticles of some commercial products which enter the environment are unsafe for humans.

Which of the statements given above is/are correct?

Answer & explanation

Answer: (d) 2 and 3

Statements 2 and 3 are correct. Statement 1 is wrong because nanoparticles (particles of about 100 nanometres or less) also form naturally, for example in volcanic plumes and by erosion, apart from those made by humans.

✗ 1. Nanoparticles form naturally: gas-phase reactions that make them occur in the atmosphere and in volcanic plumes, and erosion of clay and plant debris makes them in liquids. Human activities such as cooking and welding add more.
✓ 2. Metal-oxide nanoparticles such as nano titanium dioxide are put into sunscreens and other cosmetic products.
✓ 3. Engineered nanoparticles from consumer products are now a source of exposure, and some materials become toxic when inhaled as nanoparticles, causing lung inflammation and heart problems.

Remember · Nanoparticles (about 100 nm or less) occur naturally too. Nano titanium dioxide goes into sunscreens and cosmetics; some engineered nanoparticles are hazardous when inhaled.

Sources

European Commission (SCENIHR/GreenFacts) — Nanotechnologies, Level 2, Q4: How are nanoparticles formed? ↗ “Such reactions that generate nanoparticles occur naturally in the atmosphere , in volcanic plumes, and in human activities such as cooking, welding or smelting, and polymer manufacture.”
US EPA ExpoBox — Exposure assessment tools by chemical classes: Nanomaterials ↗ “Examples include titanium dioxide [nano-TiO2], which might be incorporated in sunscreen; silver [nano-Ag], sometimes used as an antibacterial agent;”
European Commission (SCENIHR/GreenFacts) — Nanotechnologies, Level 1 summary ↗ “Some materials could become toxic if they are inhaled in the form of nanoparticles. Inhaled nanoparticles may cause lung inflammation and heart problems.”

Question and answer: UPSC's official GS Paper I (2022, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink ·

Prelims 2022 · Q100

Easy

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?

Answer & explanation

Answer: (b) 2 and 4 only

Nitrogen oxides and sulphur dioxide cause acid rain: in the air they turn into nitric and sulphuric acids that fall with rain. Carbon monoxide and ozone are pollutants too, but they do not form these acids.

✓ 2. Nitrogen oxides (NOx) react with water, oxygen and other chemicals in the air to form nitric acid.
✓ 4. Sulphur dioxide (SO2) reacts with water, oxygen and other chemicals in the air to form sulphuric acid.
✗ 1. Carbon monoxide is a poisonous gas from incomplete burning of fuel; it is not one of the gases that make acid rain.
✗ 3. Ozone near the ground harms lungs and plants but is not an acid-rain gas.

Remember · Acid rain = SO2 + NOx turning into sulphuric and nitric acids; rain with pH below 5.6 is called acid rain.

📘 Read it in NCERT: Class 11 Political Theory, Ch 3 (practise this chapter) · Class 10 Science, Ch 2 (practise this chapter)

Sources

US EPA — What is Acid Rain? ↗ “Acid rain results when sulfur dioxide (SO 2 ) and nitrogen oxides (NO X ) are emitted into the atmosphere and transported by wind and air currents.”
NCERT Class 11 · Political Theory, Chapter 3 “They also account for three-quarters of emissions of sulphur and nitrogen oxide that cause acid rain.”
NCERT Class 10 · Science, Chapter 2 “When pH of rain water is less than 5.6, it is called acid rain.”

Question and answer: UPSC's official GS Paper I (2022, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink ·

The same topic in Mains

Conservation, pollution & EIAGS 3 syllabus

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Class 11 Political Theory, Chapter 3cited in 1 explanation
Class 10 Science, Chapter 2cited in 1 explanation

Pollution & waste

Prelims 2022 · Q44

Prelims 2022 · Q46

Prelims 2022 · Q98

Prelims 2022 · Q100

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