Unfortunately, the accuracy of the light-scattering monitor can be compromised by measuring
dust clouds with different size distributions, different dust compositions, and/or water mist/fog in
the ambient air. Consequently, when NIOSH utilizes pDR samplers, gravimetric samplers are
placed adjacent to the pDR and individual pDR dust measurements are adjusted based upon the
ratio between the average gravimetric concentration and the average pDR concentration [Thermo
Scientific 2008]. For example, if the gravimetric concentration was 1.3 mg/m3
over a 6-hour
measurement period and the pDR average concentration was 1.0 mg/m3
for the same 6 hours,
then all individual pDR measurements would be multiplied by 1.3.