Atmospheric Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 192

ambient air it may be necessary to sample for several days in order to collect suf-
fi cient material for weighing and chemical analysis, whilst instruments such as the
Scanning Mobility Particle Sizer, on the other hand, are able to scan an entire size
distribution in a matter of around one minute.
There are automated instruments available to determine the mass of airborne
particles. One commonly used instrument is the Tapered Element Oscillating
Microbalance (TEOM), within which particles are collected on a fi lter attached to
the tip of a tapered element glass tube that forms part of an oscillation microbal-
ance (Figure 5.13). The vibration frequency of the microbalance changes according
to the mass of particles deposited on the fi lter, allowing a continuous readout of
ambient concentrations with a time resolution generally of minutes. In order to
determine the mass of a specifi c size fraction, the TEOM requires a size selective
inlet, and whilst these are available for PM 10 , PM 2.5 and PM 1.0 , they are not currently
available within the nanoparticle range. There is also some evidence that whilst the
majority of fi lters are very effi cient for the collection of NPs, the fi lter used in the
TEOM may allow some penetration which would lead to under-reading of the mass
concentration (Wake, 2006 ).
Figure 5.13 Principle of operation of aTapered Element Oscillating Microbalance (TEOM).