ultrafine particle
nounUK /ˌʌltrəˈfaɪn ˈpɑːtɪkəl/
US /ˌʌltrəˈfaɪn ˈpɑːrtɪkəl/
A tiny piece of matter so small you cannot see it.
The air was full of ultrafine particles from the car exhaust.
OTHER MEANINGS
2. A particle smaller than 100 nanometres across, often studied in air-quality science.
Scientists measured ultrafine particles near the busy road.
3. A very small solid piece suspended in a gas or liquid.
The filter catches ultrafine particles but lets the air through.
4. A microscopic bit of material produced by combustion or industry.
Ultrafine particles from the factory drifted over the town.