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14.0
PARTICLE SIZE CLASSIFICATION (model pDR-1200 only)
The particle size selective cyclone of the
p
DR-1200 provides the user with two
important capabilities: a) to measure the particulate matter concentration of a
specific aerodynamic size fraction, and b) to determine the mass median size of a
particle population. These two applications will be discussed in what follows. For
both these applications, a variable measured flow rate pump is required, such as the
model
p
DR-PU (for which a separate instruction manual is provided).
14.1
Size Fractionated Monitoring
The
p
DR-1200 can be used to monitor a specific particle size fraction below a
selectable cut off equivalent aerodynamic diameter. The particle size cut point can be
selected by adjustment of the sampling flow rate. The higher the flow rate through
the cyclone the smaller the cut off particle diameter. Figure 7 is a graph showing the
dependence of the particle cut off size in micrometers as a function of the sampling
flow rate in liters per minute. The cut off size is the particle aerodynamic diameter at
which the collection efficiency of the cyclone is 50%, or conversely, the size at
which the cyclone transmission is 50%. For example, to obtain a particle size cut off
of 2.5
μ
m (i.e., PM2.5), the required sampling flow rate is 4 liters/minute. A that
flow rate only particles smaller than (approximately) 2.5
μ
m are allowed to pass into
the
p
DR-1200 sensing stage, to be monitored and then to be collected on the filter.
As can be seen on Fig. 7, the lowest particle size cut for the GK 2.05 cyclone
included with the
p
DR-1200 is about 1
μ
m, and the largest is about 12
μ
m. For
particle size classification outside this range, consult with the factory.
14.2 Particle
Sizing
The selectable particle size capability of the cyclone, in combination with the
concentration measuring capability of the photometric system of the
p
DR-1200
permits the user to determine the mass median aerodynamic particle diameter of an
aerosol, i.e., of the airborne particle population being sampled.
One simple procedure to determine the median particle size is as follows (please
refer to the graph of Fig. 7):
•
Remove cyclone from its black attachment cup and set cyclone aside
•
Start pump and sample aerosol at a flow rate between 2 and 4 liters/minute
•
Press ON key on pDR-1200 panel and after about one minute key NEXT and
then ENTER
•
After an elapsed time (ET) of about one minute, read and note TWA
concentration
•
Shut off pump
•
Plug in cyclone into its attachment cup
