1.1 Principles of Operation
The N-FRM Sampler is specifically designed to meet the US-EPA operational specifications for PM10 and
PM2.5 air sampling. To meet the EPA specifications, the N-FRM Sampler is designed to operate at 16.7
LPM and collect 24-hour samples to compare to EPA National Ambient Air Quality Standards. The ARA
N-FRM Sampler is a microprocessor-controlled portable air sampler, which can be operated manually or
programmed to collect scheduled samples. As specified by the EPA, all critical air sampling parameters
are continuously monitored and logged as time indexed 5-min averages to validate the sample. These
parameters include: flow rate, temperature, barometric pressure, and accumulated volume. Other
sampler related performance parameters are also logged. If the N-FRM Sampler is equipped with the
Real-Time Particulate (RTP) Profiler and meteorological sensors, then PM10, PM2.5, wind speed, and
wind direction are also included in the data record.
The N-FRM sampler can be easily deployed. It can be mounted on a variety of structures using our
universal mounting bracket that can be screwed, clamped, or attached to utility poles, trees, fence
posts, etc. Another option is to use a freestanding tripod.
The N-FRM Sampler is equipped to operate from either AC or DC power sources. In the DC mode, the
sampler operates from an internal battery pack. A charged battery pack is capable of operating the
sampler for about 30-40 hours. This robust capacity allows the sampler to be used in cold weather and
high altitude applications. A charger is supplied so the batteries can be re-charged in approximately one
hour.
1.2 Particulate Matter Sampling
The N-FRM Sampler can be set up for TSP, PM10, or PM2.5 particulate sampling by configuring the
sampling inlet components prior to the filter medium. To measure TSP, the omnidirectional Louvered
Inlet is all that is required. For PM10 sampling, an FRM style inertial separator (PM10 Impactor) is
added. To collect PM2.5, the sharp-cut ARA VIS-A Cyclone is attached, which physically selects particles
2.5 microns and below. Common N-FRM inlet configurations are shown in FIG. 1.
The N-FRM inertial separators (PM10 Impactor) are designed to operate at a nominal sampling rate of 1
cubic meter per hour (16.7 liters per minute). The N-FRM Sampler incorporates a microprocessor-based
active flow control to maintain the sampling rate as ambient conditions and filter loading changes. The
sampling rate is monitored and adjusted several times a second and logged at 5-min intervals along with
all other important sampling parameters.
To allow for unattended operation, the N-FRM Sampler is easily programmed to initiate and stop
sampling. For each sampling event, the N-FRM Sampler generates a summary of important sampling
parameters such as start and stop times, total sampling volume, and average ambient temperature and
pressure as well as 5-min averages of all ambient and sampler operational parameters. The logged data
file can be easily downloaded to a USB flash drive by the operator. The “csv” (comma separated value )
file can easily be imported into a spreadsheet.
