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Division 4.2.2.4 Buoyancy correction

Original text. Later amendments are not shown.

The sample and reference filter weights shall be corrected for their buoyancy in air. The buoyancy correction is a function of sampling filter density, air density and the density of the balance calibration weight, and does not account for the buoyancy of the particulate matter itself.

If the density of the filter material is not known, the following densities shall be used:

  1. (a)

    PTFE coated glass fibre filter: 2 300 kg/m3;

  2. (b)

    PTFE membrane filter: 2 144 kg/m3;

  3. (c)

    PTFE membrane filter with polymethylpentene support ring: 920 kg/m3.

For stainless steel calibration weights, a density of 8 000 kg/m3 shall be used. If the material of the calibration weight is different, its density shall be known and be used. International Recommendation OIML R 111-1 Edition 2004(E) (or equivalent) from International Organization of Legal Metrology on calibration weights should be followed.

The following equation shall be used:

mf=muncorr×1−ρaρw1−ρaρf

where:

Pef

  • is the corrected particulate sample mass, mg;

    • Peuncorr

  • is the uncorrected particulate sample mass, mg;

    • ρa

  • is the density of the air, kg/m3;

    • ρw

  • is the density of balance calibration weight, kg/m3;

    • ρf

  • is the density of the particulate sampling filter, kg/m3.

    • The density of the air ρa shall be calculated using the following equation:

    ρa=pb× MmixR× Ta
    pb

  • is the total atmospheric pressure, kPa;

    • Ta

  • is the air temperature in the balance environment, Kelvin (K);

    • Mmix

  • is the molar mass of air in a balanced environment, 28,836 g mol–1;

    • R

  • is the molar gas constant, 8,3144 J mol–1 K–1.