The word "ultrafine" means that something is extremely small or thin. It is used to describe something that is finer or more refined than normal. Full definition
«People could be exposed to dangerous levels of ultrafine particles emitted by printers if they are in an environment that is poorly ventilated and the printer operation is frequent or continuous,» says Lidia Morawska, a physicist and co-author of the study, which appears in this month's online issue of the American Chemical Society's Environmental Science & Technology. (scientificamerican.com)
Fan's most recent paper appeared in Science and investigated the influence of ultrafine aerosol particles from urban areas on severe storms. (arm.gov)
However, the health of the entire population pays a high price: substitution of gasoline for ethanol leads to a 30 % increase in the atmospheric concentration of ultrafine particulate matter, which consists of particles with a diameter of less than 50 nanometers (nm). (sciencedaily.com)