PM2.5 refers to particles with:

Aerodynamic diameter of 2.5 micrometres or less

Aerodynamic diameter of 2.5 mm or less

Why is PM2.5 more dangerous to health than the coarser PM10?

It reaches the alveoli and enters the blood

Fume is best described as:

Solid particles from condensation of vapours, e.g. welding

Solid particles from crushing and grinding

Liquid droplets such as acid mist

How does dust on leaves reduce crop yield?

It blocks sunlight and clogs stomata, reducing photosynthesis

It adds nutrients that cause overgrowth

Practice · 5 marks

Particulate pollutants: sources and effects

Short answer

Particulate matter (PM) is a mix of solid particles and liquid droplets suspended in air. Types include dust, fume, smoke, mist and fly ash. Sources include fuel combustion, brick kilns, road dust, construction and open burning. PM10 deposits in upper airways causing irritation; PM2.5 reaches alveoli and blood, causing asthma, bronchitis, heart disease and lung cancer. Dust on leaves reduces photosynthesis and soiling damages materials.

What are particulate pollutants? Describe their types, sources and the effects of PM10 and PM2.5 on human health, plants and materials.

Particulate matter (PM) is a mixture of tiny solid particles and liquid droplets suspended in air. PM10 means particles with aerodynamic diameter $\le 10\ \mu\text{m}$ and PM2.5 means $\le 2.5\ \mu\text{m}$ .

Types

Type	Meaning	Example
Dust	Solid particles from crushing/grinding, > 1 $\mu$ m	Road and cement dust
Fume	Solid particles from condensation of vapours, 0.03-0.3 $\mu$ m	Metal fumes in welding
Smoke	Solid/liquid particles from incomplete combustion, < 1 $\mu$ m	Wood and diesel smoke
Mist / fog	Liquid droplets	Sulphuric acid mist
Fly ash	Fine ash from burning coal	Thermal plants

Sources

Fuel combustion (coal, wood, diesel), brick kilns, cement and stone crushers
Road dust, construction and mining activity
Open burning of waste and crop residue
Natural: wind-blown soil, volcanoes, pollen, sea salt
Secondary particles formed from $\text{SO}_2$ , $\text{NO}_x$ and ammonia

Effects

Health: PM10 is deposited in the nose and upper airways and causes irritation and cough. PM2.5 reaches the alveoli and enters the blood. It causes asthma, bronchitis, lung cancer, heart disease and early death. Children and the elderly are most affected. Toxic particles (lead, asbestos, silica) cause specific diseases such as lead poisoning, asbestosis and silicosis.
Plants: A dust layer on leaves blocks sunlight and clogs stomata, which reduces photosynthesis and yield.
Materials and buildings: Soiling, abrasion and corrosion; acid particles attack marble and metals.
Atmosphere: Fine particles scatter light and reduce visibility (haze) and can alter rainfall and climate.

✓ Answer checked by Claude Opus 5.5 (high effort)

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