Studies of the measurement of respirable coal dusts and diesel particulate matter

Experiments were conducted to determine the optical scattering properties of respirable coal dusts and diesel particulate matter (DPM) at discrete angles in the forward direction and at light source wavelengths of 632.8 and 635 nm. In addition to the scattering data, simultaneous measurements were made of the total mass concentration of dust, DPM or mixtures of the two, and the responses of a unipolar ion chamber and a simpler, more common bipolar ion chamber typical of residential smoke detectors. The results of these experiments indicate, for respirable coal dusts, that the intensity per unit mass concentration at discrete angles in the range of 15°-30° varies linearly with mass concentration independent of the volatility of the dust, but that at larger scattering angles, intensities per unit mass concentration are affected by dust volatility. For DPM, the intensities per unit mass concentration are significantly lower. The results also indicate that the ion chambers respond significantly to DPM while there is no response to respirable coal dust, and that when mixtures of the two are present, the ion chambers respond to the DPM mass fraction only. In addition, it was found that the angular intensity distribution for respirable dusts is adequately described by classical Mie scattering theory, while for DPM classical Mie scattering is inadequate, and treatment of the particles as fractal-like aggregates yields much better agreement with the experimental data. This paper describes the experiments and their results.