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Question
What is a secondary air pollutant?
Answer
A pollutant formed in the atmosphere when primary pollutants react chemically (often driven by sunlight).
π‘ Hint
Formed by reactions
Question
What is a primary air pollutant?
Answer
A pollutant emitted directly from a source such as vehicles, power plants, or industry.
π‘ Hint
Emitted directly
Question
Give three examples of primary pollutants.
Answer
PM, CO, and NOx (also SO2 and VOCs).
π‘ Hint
Emitted directly
Question
Give two examples of secondary pollutants.
Answer
Ground-level ozone (O3) and PAN (also secondary particulate matter such as nitrates/sulfates).
π‘ Hint
Formed in air
Question
What is PM2.5 and why is it dangerous?
Answer
Fine particulate matter (<2.5 ΞΌm) that penetrates deep into lungs and can enter the bloodstream.
π‘ Hint
Small particles = high risk
Question
How does ground-level ozone (O3) form?
Answer
NOx and VOCs react in sunlight to produce ozone, a key component of photochemical smog.
π‘ Hint
NOx + VOCs + sunlight
Question
What is carbon monoxide (CO) and what causes it?
Answer
A colourless, odourless toxic gas produced by incomplete combustion, commonly from vehicle exhausts.
π‘ Hint
Incomplete combustion
Question
Name two conditions that worsen photochemical smog.
Answer
Strong sunlight and low wind (also temperature inversions and high traffic emissions).
π‘ Hint
Sun + trapped air
Question
What causes photochemical smog?
Answer
NOx + VOCs + sunlight β ozone and other oxidants, creating brown haze.
π‘ Hint
Traffic + sunlight
Question
What is a temperature inversion?
Answer
A warm air layer traps cooler air below, preventing vertical mixing and trapping pollutants near the ground.
π‘ Hint
Warm lid traps pollution
Question
What are nitrogen oxides (NOx) and why are they important?
Answer
Reactive gases (NO, NO2) produced by high-temperature combustion; they contribute to smog and acid deposition.
π‘ Hint
Combustion byproduct
Question
Why is PM2.5 considered the most dangerous particulate pollutant?
Answer
Its small size allows it to penetrate deep into the lungs and enter the bloodstream, increasing disease risk.
π‘ Hint
Deep lung penetration
Question
Which urban sector is usually the largest source of air pollution?
Answer
Transport (vehicle emissions) in most cities.
π‘ Hint
Traffic is key
Question
What meteorological factor can trap pollution near the ground?
Answer
A temperature inversion.
π‘ Hint
Warm lid effect
Question
Why is βozone good vs badβ a common exam trap?
Answer
Ground-level ozone is harmful (smog and respiratory irritant), while stratospheric ozone is beneficial (UV protection).
π‘ Hint
Same molecule, different place
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Topic 8.3 hub
Urban air pollution
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