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- Dictionaryultra-fine
adjective
- 1. extremely fine in size, texture, composition, etc.: "ultra-fine particles which are invisible to the naked eye"
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adjective
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Particulate matter of nanoscale size
Ultrafine particles are particulate matter of nanoscale size. Regulations do not exist for this size class of ambient air pollution particles, which are far smaller than the regulated PM10 and PM2.5 particle classes and are believed to have several more aggressive health implications than those classes of larger particulates. Although they remain largely unregulated, the World Health Organization ... Wikipedia