Measurement of personnel exposure to DPM is typically performed by size-selective gravimetric sampling with analytical analysis for elemental carbon. Sampling pumps, filter media and cyclones or impactors designed to provide a 1 micron diameter cut point are typically used to collect samples for weighing an analysis. The data is not immediately available after conducting sampling due to the time lag required for laboratory analysis.
Recent efforts have been aimed at developing an instrument that can measure DPM in real-time. The TSI DustTrak™ Aerosol Monitor and the SidePak™ Personal Aerosol Monitor AM510 are light scattering photometric mass measurement instruments that can be used with PM1 impactors to measure DPM in real-time. Due to the complex nature of the DPM aerosol, the capabilities and limitations of photometric mass measurement instruments must be understood for effective use.
Light scattering photometric mass measurement instruments like the DustTrak and SidePak AM510 Monitors are calibrated to a test aerosol. The monitors are calibrated to the respirable fraction of ISO 12103-1, A1 Test Dust. Photometric instrument response will differ from gravimetric mass measurement when the physical properties of the sampled aerosol differ from the calibration aerosol.
Custom calibration factors (cal factors) can be developed to adjust the instrument response for aerosols that differ from the calibration aerosol. The formula for the DustTrak and SidePak AM510 Monitors custom cal factor is:
A study was conducted to investigate a correlation between the TSI DustTrak Aerosol Monitor that performs measurements in real-time and the gravimetric samples collected with an SKC® impactor for measuring DPM in an underground metal mine in the Western US. Side-by-side sampling was performed to evaluate a correlation between the DustTrak Monitor readings and the actual gravimetric sampling results. Click here to read the study article “Evaluation of Sampling Methods to Measure Exposure to Diesel Particulate Matter in an Underground Metal Mine”
Table 1 contains the data from this study comparing the DustTrak Monitor readings to the Organic Carbon (OC), Elemental Carbon (EC) and Total Carbon (TC) mass measurements.
Figure 1 shows the correlation between the TSI DustTrak Monitor readings and the SKC Impactor measurements. The R2-0.91 indicates a good correlation between the DustTrak Monitor readings and the gravimetric measurement.
Using the custom calibration formula for the DustTrak Monitor applied to the applicable data from this study, a custom cal factor for DPM can be developed. Note: Gravimetric results listed as “less than” were omitted from the calculation.
Based on the data from this operation, the DustTrak Monitor custom cal factor for DPM as total carbon varied between 0.19 and 0.48 with an average of 0.33. Using the average 0.33 to set the instrument photometric cal factor will change the instrument response to more closely align with the gravimetric concentrations for this aerosol. This process can be followed with co-located DustTrak or SidePak AM510 Monitors and gravimetric concentration measurements for any aerosol to more closely align the light scattering photometric response to the gravimetric concentration of the sampled aerosol.
Note: The results of this study and this cal factor are not intended to be representative of all DPM measurements in all situations. Different operations should collect data with co-located gravimetric and light scattering photometric mass measurement instruments to develop similar cal factors.
Bruce K. Cantrell & Winthrop F. Watts Jr. (1997) Diesel Exhaust Aerosol: Review of Occupational Exposure, Applied Occupational and Environmental Hygiene, 12:12, 1019-1027, DOI: 10.1080/1047322X.1997.10390643.
2 Stephenson, et al; Evaluation of Sampling Methods to Measure Exposure to Diesel Particulate Matter in an Underground Metal Mine; Mining Engineering 58(8):39-45 (2006).