Section 1: Introduction
Airmetrics
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1 INTRODUCTION
The MiniVol Portable Air Sampler is an ambient air sampler for particulate matter
and non-reactive gases. The patented low flow technology used in the MiniVol was
developed jointly by the U. S. Environmental Protection Agency (EPA) and the
Lane R egional A ir Pollution A uthority in a n effort to ad dress the n eed for po rtable
air pollution sampling technology.
While n ot a referen ce meth od sam pler, the M iniVol giv es results th at closely
approximate reference method air quality data. Both accurate and precise, the
battery operated, lightweight MiniVol is ideal for sampling at remote sites or areas
without power. In addition, the low cost of the sampler allows a network of
MiniVols to be deployed at a fraction of the cost for a similar reference station
network.
The MiniVol features a 7-day programmable timer, a constant flow control system,
an elapsed time totalizer, rechargeable battery packs, and all-weather PVC
construction. The MiniVo l can be configure d to sample for jus t particulate matter,
just gases, or both simultaneously.
Principles of Operation
The MiniVol Portable Air Sampler is basically a pump controlled by a
programmable timer which can be set to make up to six "runs" within 24 hours or
throughout a week. When used outdoors it may be hung from a bracket mounted on
a variety of structures—utility poles, trees, fence posts, etc.
The sampler is equipped to operate from either AC or DC power sources. In the
DC operational mode, the sampler operates from a battery pack, thus making the
samplin g site indep endent o f line pow er. In the A C mo de the ba ttery pack is
connected to line power and mated to the sampler unit. This configuration charges
the battery while us ing AC power . The M iniVol co mes w ith two ba ttery pack s to
accomplish continuous field sampling. A charged battery pack is capable of
operating the sampler for up to 24 sampling hours on a single charge.
The sampler is equipped with two "fault circuits":
Airmetrics MiniVol Users Guide
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Airmetrics
!
A
low ba ttery circu it
automatically shuts the sampler down should the
rechargeable lea d-acid battery fail to supply sufficient voltage (below 10.3
volts) to the p ump. T his feature p rotects the b attery wh ich could be dam aged if
used continuously at low voltage. A "low-battery" indicator lights to alert the
operator of this condition.
!
A
low flow circuit
monitors the flow rate. Should excessive accumulation of
particulate m atter or som e restriction in the tubing cause the air flow to fa ll
below a specified rate, the sampler shuts down and a "low flow" indicator
lights to alert the operator.
An
Elapsed Time Totalizer
linked in parallel with the pump records the total time
in hours of pump operation.
P
ARTICULATE
M
ATTER
S
AMPLING
M
ODE
In the particulate matter (PM) sampling mode, air is drawn through a particle size
separator and then through a filter medium. Particle size separation is achieved by
impaction. Critical to the collection of the correct particle size is the correct flow
rate through the impactor. For the MiniVol, the actual volumetric flow rate must
be 5 liters per minute (5 lpm) at ambient conditions. To assure a constant 5 lpm
flow rate th rough the size sepa rator at differin g air temp eratures a nd atmo spheric
pressure s, the sam pler mu st be adjus ted for eac h samp ling projec t.
NOTE : The terms S IZE SEP ARA TOR, P RESEP ARA TOR a nd IMPA CTOR are
used inter change ably in this m anual.
Impactors are available with a 10 micron cut-point (PM
10
) and a 2.5 micron cut-
point (PM
2.5
). Operating the sampler without an impactor allows for collection of
total suspended p articulate matter (TSP ).
The inlet tube downstream from the filter takes the air to the twin cylinder
diaphragm pump. From the pump, air is forced through a standard flowmeter
where it is exhausted to the atmosphere inside the sampler body.
The program mable time r will automatically turn the pump o ff at the end of a
sampling period. The sampler must then be serviced and set up for the next
sampling period. Servicing includes removing the sampler from its hanging
bracket, remo ving the filter holder with the exposed filter inside from the sampler,
