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Ultrafine Particles in Ambient Air
Fundamentals and More
Ultraﬁne particles (UFPs) are a subclass of fine (< 1,000 nm) particles, and are generally considered to be 100 nm in size or smaller.1 Because of their tiny size, these particles are too small to contribute appreciably to mass-based measurements (PM), which are the basis of air quality regulations in many countries. UFPs come from both anthropogenic and natural sources.2
Because of their tiny size, though, they function differently in the atmosphere – and, if inhaled, within the human body – than larger particles do. Because of their influence on atmospheric science (including climate) and their effects on human health, it’s valuable to measure ultrafine particles…we can gain valuable information about human exposures, as well as greater insight into how aerosol particles evolve and behave within the atmosphere.
Learn more about the impacts of UFP’s on human health.
As noted above, mass-based measurements are almost completely ‘blind’ to the presence of UFP’s…because they’re so small, they contain very little mass. For reference, mass-based techniques measure the mass of all the particles that are present in a given volume of air.
A better way to gain insight into the presence of UFP’s is to use a number-based approach, where every particle is counted, regardless of its size. The resulting measurement is the number of particles that are present in a given volume of air.
Measuring exactly that – the number of particles present in a given volume of air – can tell you a lot about particle formation, particle transport, and human exposure. But further information is possible if you pair the ‘counting’ capability with a ‘sizing’ capability: this enables the measurement of the particle size distribution of the UFP’s.
Regardless of whether you measure the number concentration, the size distribution, or both, UFP’s should be drawn from the atmosphere using a sampling system to ensure that the sample that reaches the instrument(s) is as representative as possible.
Learn more about the fundamentals of measuring UFP’s: particle number concentration (PN), particle size distribution (PSD), and air sampling.
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