 | This article has multiple issues. Please helpimprove it or discuss these issues on thetalk page.(Learn how and when to remove these messages) (Learn how and when to remove this message)
|
Aparticulate matter sampler is an instrument for measuring the properties (such asmass concentration orchemical composition) ofparticulates in the ambient air.
Two different types of particulate matter samplers exist that measure particulate mass concentration: manual samplers and automated samplers.
Manual samplers draw a knownvolume of air through afilter. The filter is weighed on ananalytical balance before and after sampling, and the difference in weight divided by the volume of air pulled through the filter gives the mass concentration of the particulate.[1]
Automated samplers do the weighing in the field. There are two types of automated samplers in common usage: samplers that use abeta gauge for mass measurement and samplers that use atapered element oscillating microbalance (TEOM) for mass measurement.
Beta gauge particulate samplers have an appearance that is similar to areel to reeltape recorder. Air is pulled through a filter tape to accumulate a sample, the mass of the tape before and after sampling is determined by advancing the tape spot into thebeta attenuation cell.
The tapered element oscillating microbalance (TEOM) particulate sampler operates by drawing air through a filter attached at the tip of a glass tube. Anelectrical circuit places the tube intooscillation, and theresonant frequency of the tube is proportional to thesquare root of the mass on the filter.
Recently,microphone based instruments have been devised that monitornoise levels in specificfrequency bands to predict local PNC levels. Prototypes of such instruments have been tested in Europe and inBangalore.[2]
Particles of different sizes have differenthealth effects.Inertial separators are used to eliminate particles outside of the desired size range. If agas stream containing particles of different sizes is forced to turn a sharp corner, the inertia of the large particles causes them to separate from the gas stream lines. The larger particles can be collected and removed from the gas stream after collisions with the walls of the vessel.
The two common types of inertial separators are cyclones, which spin the gas stream, causing collisions of the heavier particles with the outside of the cyclone wall, and impactors, where the gas particle stream is directed at a greasedmetal plate and turned at the last moment, causing the larger particles to stick to the greased plate.
Modern particulate samplers use avolumetricflow control system that pulls air through the particle separator at thevelocity required to achieve the desired cutpoint.
Forair pollution applications, the definition of "particulate" does not include uncombinedwater, and water from a particulate sample must be removed before it is weighed. This can be done either by heating the sample toevaporate the water or by placing the sample in a lowhumidity environment before weighing.
![[icon]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aWiki_letter_w_cropped.svg) | This sectionneeds expansion. You can help byadding to it.(October 2024) |
