Medical explainer

PM2.5 vs PM10: what is the difference?

Both are particulate matter size fractions. PM10 includes particles with aerodynamic diameter up to about 10 µm; PM2.5 is the finer subset up to about 2.5 µm. The size difference changes where particles tend to deposit and often reflects different source mixtures.

PM10

≤ 10 µm

Includes coarse particles as well as the PM2.5 fraction. Larger particles are more likely than fine particles to deposit in the nose, throat and larger conducting airways, although deposition is not all-or-none.

PM2.5

≤ 2.5 µm

Fine particles can penetrate more deeply into small peripheral airways and the alveolar region. Their health relevance extends beyond respiratory symptoms to cardiovascular outcomes.

Simplified deposition map

Smaller particles can travel farther into the respiratory tract.

This is a teaching schematic, not a literal map of where every particle ends up. Deposition depends on size, shape, breathing pattern and airway anatomy.

A common confusion

PM10 does not mean “particles between 2.5 and 10 µm only.”

A PM10 concentration is the mass concentration of particles in the PM10 size fraction. PM2.5 is contained within that fraction. The coarse fraction is often approximated analytically as PM10 minus PM2.5, but a monitor displaying PM10 is not directly displaying only coarse particles.

Road / soil dust

Often contributes importantly to coarse particulate matter, although real source mixtures overlap.

Combustion

Fuel combustion is an important source of fine particulate matter and gaseous precursors that can form secondary particles.

Secondary aerosol

Some particles form in the atmosphere from gaseous precursors rather than being emitted as particles at the source.

Primary references

WHO Global Air Quality Guidelines ↗US EPA particle exposure ↗

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Particle size → lung deposition