Unit 7 Primary pollutants Tap / Space to flip
Unit 7 Emitted directly: CO, NOx, SO₂, VOCs, particulate matter (PM), lead. Mostly from combustion.
Unit 7 · 7–10% of exam
Atmospheric Pollution
Primary vs. secondary pollutants, photochemical and industrial smog, acid rain, indoor air, thermal inversions. Detailed primary/secondary tables on the priority page.
Must-know content
- Six EPA criteria air pollutants: CO, NOx, SO₂, Pb, particulate matter (PM), tropospheric ozone (O₃).
- Primary pollutants (emitted directly): CO, SO₂, NOx, VOCs, particulates, lead. Mostly from combustion.
- Secondary pollutants (formed in atmosphere): tropospheric O₃, photochemical smog, sulfuric acid (H₂SO₄), nitric acid (HNO₃), peroxyacyl nitrates (PANs).
- Photochemical smog — NOx + VOCs + sunlight → ground-level ozone. Brownish haze. Worst on hot, sunny, urban days (LA, Beijing, Mexico City).
- Industrial (sulfur) smog — SO₂ + particulates from coal burning. Gray haze. Worst in cool, damp climates (Donora 1948, London 1952).
- Thermal inversion — warm air layer traps cool polluted air below, preventing dispersion. Worsens smog in valleys.
- Acid deposition (acid rain): SO₂ + H₂O + O₂ → H₂SO₄; NOx + H₂O → HNO₃. Lowers lake & soil pH; damages forests, statues; mobilizes Al³⁺ that kills fish.
- Indoor air pollution: radon (#2 cause of lung cancer), asbestos (mesothelioma), CO (faulty heaters), formaldehyde (pressed wood), VOCs (paints, cleaners), mold.
- Clean Air Act (1970, amended 1990): sets National Ambient Air Quality Standards. Cap-and-trade for SO₂ (acid-rain program) — successful: SO₂ down 80% since 1990.
- Catalytic converters reduce CO, NOx, and VOCs from car exhaust. Required since 1975 in the US.
- Noise pollution — measured in decibels (dB). >85 dB causes hearing damage with prolonged exposure.
Example questions
MCQ Which is a SECONDARY pollutant? (A) CO (B) SO₂ (C) Tropospheric ozone (D) PM
Answer: C. Ground-level ozone is not emitted directly — it forms when NOx and VOCs react in sunlight. CO, SO₂, and PM are all primary (directly emitted by combustion or industry).
FRQ Describe how a thermal inversion intensifies air pollution.
Answer: Normally, air near the warm ground rises and disperses pollutants vertically. In a thermal inversion, a layer of warm air sits above a cooler layer near the surface, reversing the normal temperature gradient. Because the cool surface air cannot rise through the warmer air above, pollutants are trapped near the ground. This concentrates particulates and ozone, producing severe smog episodes (e.g., Donora, PA, 1948 and London, 1952). Inversions are common in valleys (LA, Mexico City) and during winter under high-pressure systems.
MCQ Which indoor air pollutant is the leading cause of lung cancer in non-smokers? (A) Asbestos (B) Radon (C) Formaldehyde (D) CO
Answer: B. Radon — a radioactive gas seeping from soil and bedrock into basements. The EPA recommends home testing and ventilation in high-radon areas.
Drill flashcards
Unit 7 Secondary pollutants Tap / Space to flip
Unit 7 Form in atmosphere from reactions: ground-level O₃, photochemical smog, sulfuric & nitric acid (acid rain).
Unit 7 Photochemical smog Tap / Space to flip
Unit 7 NOx + VOCs + sunlight → ozone (O₃) and other oxidants. Brownish haze, irritates lungs (LA, Beijing).
Unit 7 Industrial smog Tap / Space to flip
Unit 7 Particulates + SO₂ from burning coal. Gray haze. Worse in cool, damp climates (London Fog of 1952).
Unit 7 Acid rain Tap / Space to flip
Unit 7 SO₂ + NOx + H₂O → H₂SO₄ + HNO₃. Damages lakes (low pH kills fish), forests, statues, soil.
Unit 7 Particulate matter (PM) Tap / Space to flip
Unit 7 Tiny solid/liquid particles. PM2.5 (≤2.5 μm) penetrates deep in lungs. Causes asthma, heart disease.
Unit 7 Carbon monoxide (CO) Tap / Space to flip
Unit 7 Colorless, odorless. From incomplete combustion. Binds hemoglobin → suffocation. Indoor cause: faulty heaters.
Unit 7 Thermal inversion Tap / Space to flip
Unit 7 Warm air layer traps cool polluted air below, preventing dispersion. Worsens smog in valleys (LA, Mexico City).