AN-FT-007-A “Aerosol Correction Factors”

Corrections Factors for Filter Leakage Testing using an Aerosol photometer and Laskin nozzle generator.

In general usage, a Laskin nozzle type III-A generator requires no pressure adjustment to obtain valid results, provided the following conditions are met:

1. the aerosol photometer in use has internal reference settings for the chosen aerosol reagent allowing the upstream aerosol concentration to be quantified.
2. the 100% baseline is set by directly sampling the upstream challenge allowing operation of the photometer as a ratio measurement device.

When using PAO-4, and calculating the aerosol generating capacity of a Laskin III-A nozzle generator, an operating pressure of 23 psi should be maintained in place of the customary 20 psi used with DOP (DEHP).

The specific gravity and viscosity of different aerosol reagents require pressure adjustments to produce the same weight of aerosol per volume of air, mg/m3 or µg/l, as PAO-4 or DOP.

Example:  For purposes of calculating output, continuing to use the 20 PSI value associated with DOP while testing using PAO-4 will result in an overstatement of the aerosol concentration by approximately 8%.

Aerosol Correction Factors
Aerosol Generators
Nozzle pressure values discussed below are intended for use when liquids are substituted for aerosol production in place of PAO-4 or DOP and the aerosol output of a Type III-A Laskin nozzle generator must be calculated.

Example:

• PAO-4 @ 23 psi nozzle pressure, mixed with a dilution airflow of 135 cfm, yields 100 mg/m3
• DOP @ 20 psi nozzle pressure, mixed with a dilution airflow of 135 cfm, yields 100 mg/m3

13,500 X (# of nozzles in use) ÷ total filter airflow (CFM) = Aerosol concentration (mg/m3)

Aerosol Reagent	Chemical Abstracts Service #	Nozzle Pressure (PSI)
DOP/DEHP	117-81-7	20
PAO-4	68037-01-4 or 68649-12-7	23
DOS/DEHS	122-62-3	24.4
White mineral oil	8042-47-5	22
Polyethylene glycol	24322-68-3	26.6
Paraffin oil	8012-95-1	24.2
Corn oil	8001-30-7	23.4

It should also be noted that operation of the Laskin nozzle generator at different pressures will also change the volume of compressed air needed to maintain pressure.  Portable air compressors will need to be sized accordingly.

Figure 1 – Laskin III-A air consumption (volume vs. pressure)

Note: 
Adjustment of the Laskin nozzle pressure to accommodate the aerosol reagent in use is independent of the Aerosol Photometer internal reference reagent setting discussed below. 

 Aerosol Photometers
Photometer internal reference factors are multipliers used to adjust the reference setting required for a 100% reading.  They are only necessary when using an aerosol reagent not calibrated as an internal reference setting during factory calibration.
There are two examples that follow, one for analog and one for digital photometers.

Note: Both Analog and Digital photometers apply the internal reference factor to the 100% reference value used for DOP.  An analog photometer with only one internal reference setting, adjusted for other than DOP, cannot use these values without interpolation.

Aerosol Reagent	Chemical Abstracts Service #	Factor	Refractive Index	Density (g/ml)
DOP/DEHP	117-81-7	1.00	1.485	0.980
PAO-4	68037-01-4 or 68649-12-7	0.73	1.456	0.819
DOS/DEHS	122-62-3	0.96	1.448	0.915
Ondina EL	8012-95-1	0.79	1.467	0.851
White mineral oil	8042-47-5	0.90	1.471	0.840
Polyethylene glycol	24322-68-3	1.11	1.465	1.128
Paraffin oil	8012-95-1	0.89	1.466	0.848
Corn oil	8001-30-7	0.88	1.464	0.918

Liquid consumption rates for Laskin III-A nozzles using PAO-4 and DOP:
(Multiply consumption rate, listed below, by the number of nozzles in use)

28 ml/hour of PAO-4 liquid volume consumption per nozzle when operating @ 23 psi
23.4 ml/hour of DOP (DEHP) liquid volume consumption per nozzle when operating @ 20 psi

Please contact ATI with any further questions or comments.