Which pollutant is a secondary pollutant?

Ozone formed by reactions in the atmosphere

According to the answer, air pollution exists when substances in the outdoor air are present:

In quantities and durations harmful to health, plants, animals, materials or the environment

Only if they are of human origin

Which set contains only natural sources of air pollution?

Volcanoes, forest fires, dust storms

Brick kilns, vehicles, volcanoes

Crop residue burning, pollen, cement plants

Lightning, power plants, sea spray

Why are anthropogenic sources the main concern?

They emit gases that natural sources never emit

They are always larger in total than natural sources worldwide

They only emit primary pollutants

Practice · 5 marks

Classification and sources of air pollutants

Short answer

Air pollution is the presence of harmful substances in outdoor air. Pollutants are classified as primary (emitted directly, e.g. SO2, CO, fly ash) and secondary (formed in the atmosphere, e.g. ozone, PAN). Natural sources include volcanoes, forest fires and dust storms; anthropogenic sources include fuel combustion, vehicles, industry, agriculture and domestic burning.

Define air pollution. Classify air pollutants and explain with examples the natural and anthropogenic sources of air pollution.

Air pollution is the presence in the outdoor atmosphere of one or more substances (gases, particles, vapours) in quantities and for durations that are harmful to human health, plants, animals, materials or the environment.

Classification of pollutants

Primary pollutants are emitted directly from a source, e.g. $\text{SO}_2$ , CO, NO, hydrocarbons, fly ash, soot.
Secondary pollutants are formed in the atmosphere by reactions between primary pollutants, e.g. ozone, PAN, sulphuric acid mist, $\text{NO}_2$ from NO.

Basis	Types	Examples
Physical state	Particulate	Dust, fume, smoke, mist, fly ash
Physical state	Gaseous	$\text{SO}_2$ , $\text{NO}_x$ , CO, $\text{CO}_2$ , $\text{O}_3$ , VOCs
Origin	Natural / anthropogenic	Volcano / vehicles
Source geometry	Point / line / area	Chimney / highway / city

Natural sources

Volcanic eruptions (ash, $\text{SO}_2$ , $\text{H}_2\text{S}$ )
Forest fires (smoke, CO, $\text{CO}_2$ )
Dust storms, sea spray, pollen and spores
Decay of organic matter (methane, $\text{H}_2\text{S}$ ) and lightning (NO)

Anthropogenic (man-made) sources

Combustion of fuels in power plants, industries and homes: $\text{SO}_2$ , $\text{NO}_x$ , fly ash, CO.
Transport: CO, hydrocarbons, $\text{NO}_x$ , lead (where leaded fuel is used), PM from diesel engines.
Industrial processes: cement, brick kilns, steel, chemical plants, mining (dust, fumes, acid gases).
Agriculture and waste: burning of crop residue, open burning of waste, methane and ammonia.
Domestic: cooking with biomass, kerosene and coal.

Anthropogenic sources are the main concern because they are concentrated in cities and are continuous.

✓ Answer checked by Claude Opus 5.5 (high effort)

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