Q.Photochemical smog contains
🔒You're viewing a preview — the full solution, concept, methods & PYQ mapping are locked.
🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Air Pollution
Air Pollution: A First Look
Imagine you are sitting in a closed room with a friend who just lit a cigarette. The air starts to feel heavy. Your throat tickles. Your eyes sting. That is air pollution in its most direct form — something unwanted has entered the air you breathe, and your body is telling you it does not like it.
Now step outside. That same idea scales up. The air around us is not empty space — it is a mixture of gases (mostly nitrogen and oxygen) plus tiny particles of dust, pollen, and water vapour. When we burn fuels in factories, vehicles, or homes, we add new substances to this mixture: smoke, soot, invisible gases like carbon monoxide and sulphur dioxide. When these reach a concentration high enough to harm living things or damage the environment, we call it air pollution.
The key shift in thinking: air is not "pure" by default. It always contains some dust and natural gases. Pollution is about too much of the wrong thing in the wrong place.
The Precise Definition
Air pollution is the introduction into the atmosphere of substances — called pollutants — that have harmful effects on human health, other living organisms, or the built environment. These pollutants can be:
- Gases (e.g., carbon monoxide, nitrogen dioxide, sulphur dioxide, ozone)
- Particulate matter (tiny solid or liquid droplets suspended in air — dust, smoke, soot)
- Biological molecules (pollen, mould spores — though these are natural, they become "pollution" when they cause harm)
The key word is harmful. A little bit of smoke from a campfire is not pollution if it disperses quickly. But the same smoke trapped in a valley on a windless day, accumulating hour after hour — that is pollution.
Two Main Sources
| Source type | Examples | Why it matters |
|---|---|---|
| Natural | Volcanic eruptions, forest fires, dust storms, pollen | Usually short-lived or localised; we cannot control them |
| Anthropogenic (human-made) | Vehicle exhaust, factory chimneys, burning of coal/wood, agricultural burning | This is where most of our pollution problems come from — and what we can fix |
Photochemical smog is not a single pollutant but a mixture of secondary pollutants formed when sunlight acts on vehicle exhaust, so each of the substances listed is genuinely present in it. …
Photochemical smog is a mixture of secondary pollutants — PAN, ozone, and NO2 — formed by sunlight-driven reactions of primary pollutants.
Note on scope: this question tests air-pollution chemistry (photochemical smog), part of the 'Environmental Issues' unit. That specific unit is not part of the current rationalised NCERT syllabus this platform's chapter content is built from, so a chapter-linked lesson isn't available here — but the question itself has a clear, well-established answer, given below.
Photochemical smog forms when primary pollutants from vehicle/industrial exhaust — nitrogen oxides and unburnt hydrocarbons — react with each other in the presence of sunlight (UV radiation), producing a cocktail of secondary pollutants. Its major components include:
- PAN (peroxyacetyl nitrate) — a strong eye and respiratory irritant. …
- CBSE 2026Set ANNUAL1 markMCQQ.Plant indicator for SO2 pollution is :(a) Gladiolus, Eucalyptus(b) Petunia, Chrysanthemum(c) Robinia pseudoacacia, Casuarina(d) Lichens, Rose
›Reveal solutionSolution
Lichens are the textbook bio-indicator of SO2 pollution, making option (d) the correct pairing among the four.
Working
Certain plants and plant-like organisms are used as biological indicators of specific air pollutants because they show visible damage (chlorosis, necrosis, reduced growth, or local disappearance) at pollutant concentrations too low to be obvious by other means. For sulphur dioxide (SO2), the single most widely cited bio-indicator is the lichen -- a symbiotic association of a fungus and an alga/cyanobacterium. Lichens lack a waxy cuticle and absorb gases (including SO2) directly over their whole surface, and their photosynthetic algal partner is especially sensitive to sulphite toxicity; as a result, lichens are killed or fail to establish in areas with even modest SO2 pollution, and the sharp fall in lichen diversity around industrial/urban centres (sometimes called a 'lichen desert') is a classic, long-used indicator of chronic SO2 pollution. Sensitive flowering ornamentals such as rose have also been used in pollution-monitoring gardens as visible SO2-sensitive indicator plants alongside lichens. Checking the oth …
- CBSE 2023Set 64/3/11 markMCQQ.Which one of the following is the cause of acid rain ? (A) Land pollution (B) Water pollution (C) Air pollution (D) Noise pollution
›Reveal solutionSolution
Acid rain is caused by air pollution, specifically when certain gases released into the atmosphere mix with rainwater.
Acid rain is a direct consequence of air pollution. When we burn fossil fuels — coal, oil, petrol — in factories, power plants, and vehicles, they release gases like sulphur dioxide and nitrogen oxides into the air. These gases rise high into the atmosphere, where they react with water vapour, oxygen, and sunlight. This chemical reaction turns them into sulphuric acid and nitric acid. When it rains, these acids come down with the raindrops, making the rain acidic — hence the name "acid rain."
NoteNormal rain is already slightly acidic because carbon dioxide in the air dissolves in it to form weak carbonic acid. But acid rain is far more acidic, with a pH below 5.6, and that extra acidity comes from human-made air pollutants.
So the root cause is not something on the ground like garbage or sewage. Land pollution (A) involves solid waste and chemicals dumped on soil, but those don't rise into the sky to form acid rain. Water pollution (B) is about contaminants in rivers, lakes, and oceans — again, not airborne. Noise pollution (D) is about sound, which has nothing to do with chemistry in the clouds. …
- CBSE 2023Set ANNUAL1 markQ.Which device is used to clean both dust and gases from polluted air?
›Reveal solutionSolution
A scrubber is an air-pollution control device that removes both particulate matter (dust) and gaseous pollutants from industrial exhaust before it is released.
A scrubber works by passing polluted exhaust gas through a spray or bed of a scrubbing liquid (often water or an alkaline solution). Fine dust and particulate matter are trapped/washed out by the liquid droplets, while acidic or other soluble gaseous pollutants (such as SO2) are absorbed and neutralised by chemical reaction with the scrubbing liqu …
- CBSE 2019Set 64/2/11 markQ.How does air pollution affect human health ?(OR)How does noise pollution affect human health ?
›Reveal solutionSolution
Part (a): Air pollution causes respiratory diseases (asthma, bronchitis, lung cancer) and heart problems, plus eye and throat irritation.
Part (b): Noise pollution causes hearing loss and deafness and raises stress, disturbing sleep and causing high blood pressure and poor concentration.
Part (a)
Air pollution affects human health mainly by being breathed in. The respiratory system is hit first: polluted air irritates and inflames the airways, causing coughing, wheezing and breathlessness, and it triggers or worsens asthma, bronchitis and chronic lung diseases. Fine particulate matter (PM2.5) is especially dangerous because it penetrates deep into the lungs, and long-term exposure raises the risk of lung cancer. The cardiovascular system is also affected — fine particles entering the bloodstream cause inflammation, hardening of the arteries and higher blood pressure, increasing the risk of heart attacks and strokes, while carbon monoxide reduces the blood's oxygen-carrying capacity. In addition, pollutants cause eye and throat irritation, headaches and fatigue. Children, the elderly and people with existing heart or lung conditions suffer the most.
Part (b) …
- CBSE 2018Set ANNUAL1 markMCQQ.Photochemical smog contains(a) PAN(b) Ozone(d) Nitrogen dioxide(e) All of the above
›Reveal solutionSolution
Photochemical smog is a mixture of secondary pollutants — PAN, ozone, and NO2 — formed by sunlight-driven reactions of primary pollutants.
Note on scope: this question tests air-pollution chemistry (photochemical smog), part of the 'Environmental Issues' unit. That specific unit is not part of the current rationalised NCERT syllabus this platform's chapter content is built from, so a chapter-linked lesson isn't available here — but the question itself has a clear, well-established answer, given below.
Photochemical smog forms when primary pollutants from vehicle/industrial exhaust — nitrogen oxides and unburnt hydrocarbons — react with each other in the presence of sunlight (UV radiation), producing a cocktail of secondary pollutants. Its major components include:
- PAN (peroxyacetyl nitrate) — a strong eye and respiratory irritant. …
- CBSE 2016Set ANNUAL1 markQ.Why PUC is mandatory for all vehicles?
›Reveal solutionSolution
PUC checks keep vehicle emissions within legal limits, curbing air pollution and its health effects.
Vehicles burning petrol or diesel release polluting gases such as carbon monoxide, unburnt hydrocarbons, oxides of nitrogen, and particulate matter, all of which degrade air quality and contribute to respiratory diseases, smog formation and global warming. A PUC (Pollution Under Control) certificate is issued only after a vehicle's exhaust emissions are tested and found to be within government-prescribed limits. Making this mandatory for all vehicles ensures that poorly maintained or high-polluting vehicles are identified, repaired or taken off the road, thereby reducing the overall vehicular contribution to urban air pollution, safeguarding public he …
🎓Unlock everything free for 14 days
- ✓Full step-by-step solutions
- ✓Concept-first explanations
- ✓Methods, shortcuts & mistakes
- ✓PYQ mapping + timed mock tests
Full access for 14 days. No credit card required.