5. Calibration
All particle monitors based on light scattering require a site calibration for optimum accuracy. This is
because the average density and light scattering behaviour of dust particles will vary from site to site.
This adjustment is sometimes known as a “K-factor”. Aeroqual recommends a site calibration be
performed at the time of initial installation and then every 6-12 months. Calibration is performed by co-
locating the Dust Profiler with a Reference Particulate Matter measurement system and adjusting the
Gain of the particle monitor so the average reading matches that of the Reference Instrument. A list of
Reference instruments can be found at:
http://www.epa.gov/ttnamti1/files/ambient/criteria/reference-equivalent-methods-list.pdf
Install the Dust Profiler beside the Reference instrument. Make sure both instruments are setup
correctly. Two procedures are given below depending on whether the reference instrument is a
gravimetric or continuous instrument.
Procedure overview for Gravimetric Reference Instrument
1. Weigh a reference filter and install into the Reference instrument.
2. Leave the Dust Profiler and Reference instrument running for at least 24 hours until a weighable
quantity of particulate matter sample has been collected.
3. Check the sample flows of both instruments to ensure they are within specification.
4. Remove the Reference filter and re-weigh
5. Download the Dust Profiler PM data for the calibration period.
Calculations
1. Reference Filter Weight of PM (ug):
PM(Ref) = (filter weight at finish)
– (filter weight at start)
2. Volume of air sampled by reference sampler (m3)
Volume(Ref) = minutes of test * Flow Ref (LPM) / 1000
3. Calculate average reference PM density (ug/m3)
AvPM(Ref) =
PM(Ref)/ Volume(Ref)
4. Calculate average AQM60 PM (ug/m3):
AvPM(Dust Profiler) = sum(PM readings over test period)/number of readings
Procedure overview for a Continuous Reference Instrument
1. Leave the Dust Profiler and Reference instrument running for at least 24 hours
2. Check the sample flows of both instruments to ensure they are within specification.
3. Download the Dust Profiler and Reference instrument data for the calibration period
Calculations
1. Calculate average Dust Profiler PM (ug/m3):
AvPM(Dust Profiler) = sum(PM readings over test period)/number of readings
2. Calculate average Reference PM (ug/m3):
AvPM(Ref) = sum(PM readings over test period)/number of readings
Calculation of Dust Profiler Gain
1. Calculate K factor
K factor
= AvPM(Ref) / AvPM(Dust Profiler)
2. You should then apply this to the Gain Factor on all the PM channels.
new GAIN = old GAIN x K Factor
