IB ESS: What Causes Smog?

Smog becomes likely when these inputs combine with the right conditions: strong sunlight, weak wind, and sometimes a city layout that traps air.

If you want exam-style practice on the exact wording and command terms, use the 6.3 Photochemical smog Questionbank and the broader ESS Questionbank by topic.

Two main types of smog (know both for IB ESS)

Photochemical smog (sun-driven)

Photochemical smog is common in warm, sunny cities with heavy traffic. Sunlight triggers reactions involving NOx and VOCs, creating:

• Tropospheric ozone (O3) (a lung irritant)

• PANs (peroxyacyl nitrates) and other oxidants

• Nitric acid and secondary particles that add to haze

Key idea for IB ESS: sunlight doesn’t “add pollution” -- it transforms it.

Industrial (sulfurous) smog (fuel-driven)

Industrial smog is linked to burning coal or sulfur-rich fuels in cooler, humid conditions. SO2 and particulates mix with water droplets and stagnant air to form dense gray smog. Historically, this was associated with older industrial cities and winter pollution episodes.

To keep the atmosphere context clear, revise the foundations in 6.1 Introduction to the atmosphere and the companion 6.1 notes.

How smog forms (the simple exam explanation)

For photochemical smog, your cleanest explanation is:

• UV light breaks NO2 into NO + O

• The free oxygen atom joins O2 to form O3 (ozone)

• VOCs help recycle NO back into NO2, allowing ozone to keep accumulating

Then add the physics: temperature, wind, and topography control whether pollutants disperse or build up.

Effects of smog (link to ESS systems thinking)

In IB ESS, impacts score best when you show multiple perspectives:

• Human health: eye irritation, asthma exacerbation, reduced lung function, cardiovascular stress

• Ecosystems: ozone damages leaf tissue, lowering photosynthesis and crop yields; acid-forming pollutants stress soils and waters

• Economic costs: healthcare burdens, lost productivity, reduced visibility affecting transport and tourism

Management and prevention (3 strategies to memorize)

• Cut NOx and VOCs at source: catalytic converters, low-emission zones, fuel standards

• Shift energy systems: renewables reduce combustion emissions and co-pollutants

• Urban planning: public transport, congestion reduction, and greener streets reduce exposure hotspots

To turn this into marks, practice evaluation-style responses in RevisionDojo’s Questionbank, then ask AI Chat to point out missing links (cause -> process -> impact -> management). When you want realism, build a timed set using Mock Exams and Predicted Papers, and use Grading tools to tighten your structure.

Final takeaway for IB ESS students

Smog is what you get when emissions meet sunlight and still air: chemistry plus geography plus choices. If you can explain the ingredients, describe the photochemical steps, and evaluate a few realistic management strategies, you’ve basically built the full IB ESS answer.

To lock it in, study the core pages on IB ESS resources, drill targeted sets in the 6.3 Photochemical smog Questionbank, and use RevisionDojo’s Study Notes, Flashcards, AI Chat, Tutors, Coursework Library, Grading tools, Predicted Papers, and Mock Exams to turn understanding into marks.

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