Section 1: Introduction
Airmetrics
3
and attaching a new filter holder with a fresh filter. The battery pack is also
changed at this time.
The sampling technique used by the MiniVol is a modification of the PM
10
reference me thod described in the U. S. Co de of Federal R egulations (40 C FR part
50, Appendix J). Under this criteria, a PM
10
sample r must ha ve: 1) a sam ple air
inlet system to provide particle size discrimination, 2) a flow control device
capable of maintaining a flow rate within specified limits, 3) means to measure the
flow rate during the sampling period, and 4) a timing control device capable of
starting and stopping the sampler.
The Airm etrics MiniVo l Portable Air Sam pler meets all of these specifications. It
is equipp ed with: 1 ) an inlet im pactor ca pable of se parating p articulate m atter to
#
10 µm, 2) a flow control device w hich will maintain a specified flow rate, 3 ) a
flowmeter to measure the flow rate during the sampling period, 4) an elapsed time
meter, and 5) a programmable timer that starts and stops the sampler unattended.
The MiniVol's flow rate is generally less than the flow rates used by reference
method devices. The lower rate results in a greater deviation in accuracy at low
concentrations of particulate matter where precision can be lost through the
handling and we ighing of a minute p articulate sa mple. H oweve r, at high pa rticulate
concen trations the s ampler produce s results tha t are precise and com parable to
reference method samplers.
While th e MiniV ol's sam pling m ethod is no t a referenc e or equiv alent me thod, it
has proven to be an excellent indicator of absolute ambient PM
10
concentrations.
Although the method used by portable PM
10
sampling does not wholly conform or
comply with the reference method , the data collected by the sampler still serve as a
useful supplement to data generated by PM
10
reference methods.
I
NTEGRATED
G
AS
S
AMPLING
M
ODE
In the integrated gas sampling mode, the sampler can accommodate one or two bag
modules. The bags may be filled one at a time or simultaneously within a
programmable period. There are two circuits which control the gas sampling:
1.
A tuneable intervalometer, or pulse circuit, determines the rate at which a bag
is filled. The circuit sends an electronic pulse to open a solenoid on the valve
Airmetrics MiniVol Users Guide
4
Airmetrics
driver boa rd. The d uration of e ach pulse can be ad justed from approxim ately
50 to 750 milliseconds. The pulses can also be adjusted for frequency, from
one pulse eve ry 15 second s to continuously o n.
2.
A bag sequencer determines which of the two bags is being filled during any
program med inte rval.
While the bags that are supplied with the samplers are made of relatively non-
reactive Tedlar® (polyvinyl fluoride), other parts of the air path are made of PVC,
polyethylene, silicone rubber, and other substances that are more reactive.
Consequently, you should not use the MiniVol to collect gas samples that are to be
analyzed for reactive gases like ozone or sulfur dioxide.
In the gas sampling mode, the air that is used to fill the bags is diverted from the
normal air path just before the air is vented into the sampler case—at the end of the
air path. Because of this, you may simultaneously collect a PM sample (the filter
holder is situated at the beginning of the air path) while collecting a gas sample.
