I N S T R U M E N T S

AIR QUALITY (cont'd)

INSTRUMENT COMPONENTS

Particle Selection - The Inlet

Air comes in the top through an inlet that selects only particles that are smaller than the specified diameter. For PM-10, only inlet is a separator that uses properties of the flow of air to allow only particles that are less than 10 microns to enter the instrument. For PM-2.5, a second separator is added, called a Very Sharp Cut Cyclone. This inlet traps all particles that are over 2.5 microns and allows only the smallest particles to enter the instrument.
 
Measuring The Mass Concentration

The final product for each of the instruments is the mass of particles that are in a volume of air, measured in micrograms per cubic meter.

The instrument has 4 main components:

       • The pump pulls the air through the inlet into the instrument

       • The control unit precisely regulates the volume of air flowing through the unit and ensures proper           instrument operation

       • The weighing unit measures the mass of particles that are drawn through the unit and deposited on           a filter

       • The filter dynamics measurement system monitors changes in the mass of particles that are due           to ongoing chemical changes

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