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Q54 (IAS/2022) Environment & Ecology › Pollution & Conservation › Air quality standards Official Key

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?

Result
Your answer: —  ·  Correct: B
Explanation

The correct answer is Option 2 (1 and 4 only). This is based on the 2021 WHO Air Quality Guidelines and fundamental atmospheric chemistry.

  • Statement 1 is correct: The WHO updated its Global Air Quality Guidelines in 2021, lowering the recommended limits. The annual mean for PM₂.₅ is now 5 µg/m³ and the 24-hour mean is 15 µg/m³.
  • Statement 2 is incorrect: Surface-level ozone is a photochemical pollutant formed by the reaction of precursors (NOx and VOCs) in the presence of sunlight. Therefore, ozone levels peak during sunny, hot, and stagnant weather, not during "inclement" (stormy or rainy) weather.
  • Statement 3 is incorrect: While PM₁₀ can settle deep in the lungs, it is generally too large to cross the blood-air barrier. It is PM₂.₅ (fine particulate matter) that is capable of penetrating the lung barrier and entering the bloodstream.
  • Statement 4 is correct: High concentrations of ozone are potent respiratory irritants. They can cause airway inflammation, reduce lung function, and are well-documented triggers for asthma attacks.
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PROVENANCE & STUDY PATTERN
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Don’t just practise – reverse-engineer the question. This panel shows where this PYQ came from (books / web), how the examiner broke it into hidden statements, and which nearby micro-concepts you were supposed to learn from it. Treat it like an autopsy of the question: what might have triggered it, which exact lines in the book matter, and what linked ideas you should carry forward to future questions.
Q. 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 …
At a glance
Origin: Books + Current Affairs Fairness: Low / Borderline fairness Books / CA: 2.5/10 · 7.5/10
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This is a 'Hybrid Trap': it combines a hard data memorization check (Statement 1: WHO 2021 Update) with standard static concepts (Statement 2 & 4: Ozone formation/Health). It punishes aspirants who read news headlines ('WHO updates guidelines') but failed to memorize the specific summary table.

How this question is built

This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.

Statement 1
According to the WHO Air Quality Guidelines, what are the recommended 24‑hour mean and annual mean concentration limits for PM2.5 (µg/m³)?
Origin: Web / Current Affairs Fairness: CA heavy Web-answerable

Web source
Presence: 5/5
"PM₂.₅, µg/m³ Annual 35 25 15 10 5 PM₂.₅, µg/m³ 24-hour a 75 50 37.5 25 15"
Why this source?
  • This is the WHO summary table of recommended 2021 AQG levels showing both annual and 24‑hour values for PM2.5.
  • It lists the AQG (most stringent) levels: 5 µg/m³ (annual) and 15 µg/m³ (24‑hour).
Web source
Presence: 5/5
"Interim targets set annual average thresholds at 5 µg/m³ for PM₂.₅ ... and 24-hour averages at 15 µg/m³ for PM₂.₅"
Why this source?
  • This World Bank document cites the WHO targets and repeats the recommended AQG values.
  • It explicitly states the annual PM2.5 target is 5 µg/m³ and the 24‑hour target is 15 µg/m³.

Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 5: Environmental Pollution > c) National Air Quality Index > p. 70
Strength: 4/5
“(c) National Air Quality Index . National Air Quality index 'aras launched by the Prime Minister in April, 2015 starting with four cities to disseminate air quality information. The AQI has six categories of air quality, viz Good, Satisfactory, Moderately Polluted, Poor, Very Poor and Severe. Each of these categories is associated with likely health impacts. AQI considers eight pollutants (PMro, PM 2.S, NOz, SOz, CO, O3, NH3 and Pb) for which (up to z4-hourly averaging period) National Ambient Air Quality Standards are prescribed.”
Why relevant

States that the National Air Quality Index considers PM2.5 and refers to averaging periods 'up to 24-hourly averaging period', highlighting that PM2.5 guidelines are specified for 24‑hour means.

How to extend

A student could use this to focus on WHO guideline values expressed for 24‑hour averages and compare national AQI categories to WHO 24‑hour limits.

Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 5: Environmental Pollution > a) National Air Quality Monitoring Programme > p. 69
Strength: 4/5
“(a) National Air Quality Monitoring Programme • e In India, the Central Pollution Control Board (CPCB) has been executing a nationwide programme of ambient air quality monitoring known as National Air Quality Monitoring Programme (NAMP) • The National Air Quality Monitoring Programme (NAMP) is undertaken in India • (i) to determine status and trends of ambient air quality; • (ii) to ascertain the compliance of NAAQS; • (iii) to identify non-attainment cities; • (iv) to understand the natural process of cleaning in the atmosphere; and • (v) to understand the impact of pollution on human health. All Rights Reserved. No part of this rDaterial ma,v be reproduced in any form or by any neans, rvithout permission in lriting”
Why relevant

Describes India's National Air Quality Monitoring Programme (NAMP) and its role in ascertaining compliance with National Ambient Air Quality Standards (NAAQS), implying the practice of comparing measured PM2.5 to defined annual and short‑term standards.

How to extend

A student could look up WHO AQG numerical annual and 24‑hour PM2.5 values to compare against national NAAQS and NAMP monitoring results.

Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 5: Environmental Pollution > BS VI norms > p. 72
Strength: 3/5
“As of April 1, 2020, the current emission standard in India mandates that all newly manufactured, sold, and registered cars in the country must adhere to the BS-VI norms. • r BS-VI engines emit particulate matter (PM ≤ 20 to 4a micrograms per cubic meter) within a range of 20 to 4a micrograms per cubic meter. • r The amount of sulfur released into the atmosphere by BS-VI-compliant engines has been significantly reduced, decreasing from 5o parts per million (ppm) to just 10 ppm.”
Why relevant

Gives numeric particulate emissions for BS‑VI engines (20–40 µg/m3), providing a real-world magnitude for PM concentrations used in regulatory contexts.

How to extend

A student could use these magnitudes as a baseline to judge whether WHO guideline values (annual/24‑hour) are more or less stringent than typical regulatory/technical emission-related concentrations.

Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 17: Contemporary Issues > ENVIRONMENTAL DEGRADATION > p. 57
Strength: 3/5
“ultraviolet B (UV-B) radiation that can increase the occurrence of some forms of skin cancer, cataracts and other diseases of eye (Fig. 17.14). Analysis by Centre for Science and Environment (CSE) reveals that the capital city is experiencing greater ozone pollution. The eight hour standard for ozone exposure is 100 micrograms per cubic meter. The levels of ozone have exceeded by 16% (122 µg/m3) as against 5% (106 µg/m3) in 2018. Delhi's hotspots have been identified as Najafgarh (92%), Sri Aurbindo Marg (87%), Narela (80%), Bawana (78%), Siri Fort (76%). (Source: T.O.I.; June 20, 2019) (iv) Air, Water, Soil, and Noise Pollution: The quality of air, water, and soil is depleting both in the urban and the rural areas.”
Why relevant

Provides an example of an air quality standard (8‑hour ozone = 100 µg/m3), showing that health‑based guidelines are often stated as specific µg/m3 limits for defined averaging times.

How to extend

A student could infer that WHO similarly states PM2.5 limits as numeric µg/m3 values tied to averaging periods (annual and 24‑hour) and seek those specific numbers for direct comparison.

Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 29: Environment Issues and Health Effects > Note; > p. 440
Strength: 2/5
“• T$PM Total Suspended Particulate Matter• RPM Respirable Particulate Matter• YOCs Volatite Organic Compounds• HCNYapours * Hydrogen Cyanide”
Why relevant

Lists particulate matter (TSP, RPM) as major pollutants, underlining that particulate fractions like PM2.5 are standard categories monitored and regulated.

How to extend

A student could use this to justify searching for standard guideline values specifically for PM2.5 (as a recognized pollutant fraction) expressed for annual and 24‑hour means.

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