(a) General. Correct PM sample media for their buoyancy in air if you weighthem on a balance. The buoyancy correction depends on the sample media density, the density of air, and the density of the calibration weight used to calibrate the balance. The buoyancy correction does not account for the buoyancy of the PM itself, because the mass of PM typically accounts for only (0.01 to 0.10)% of the total weight. A correction to this small fraction of mass would be at the most 0.010%.
CFR 40-1065.690-2014 history
2014CFR 40-1065.690-2014 Protection of Environment. Part1065:Engine-testing procedures. Section1065.690:Buoyancy correction for PM sample media.