Studies of the measurement ofrespirable coal dusts and diesel particulatematter

Abstract

Experiments were conducted to determine the optical scatteringproperties of respirable coal dusts and diesel particulate matter (DPM) at discrete angles in the forward direction and atlight source wavelengths of 632.8 and 635 nm. In addition tothe scattering data, simultaneous measurements were made of thetotal mass concentration of dust, DPM or mixtures of the two,and the responses of a unipolar ion chamber and a simpler, morecommon bipolar ion chamber typical of residential smokedetectors. The results of these experiments indicate, forrespirable coal dusts, that the intensity per unit massconcentration at discrete angles in the range of 15°-30°varies linearly with mass concentration independentof the volatility of the dust, but that at larger scatteringangles, intensities per unit mass concentration are affected bydust volatility. For DPM, the intensities per unit massconcentration are significantly lower. The results also indicatethat the ion chambers respond significantly to DPM while thereis no response to respirable coal dust, and that when mixturesof the two are present, the ion chambers respond to the DPMmass fraction only. In addition, it was found that the angularintensity distribution for respirable dusts is adequatelydescribed by classical Mie scattering theory, while for DPMclassical Mie scattering is inadequate, and treatment of theparticles as fractal-like aggregates yields much betteragreement with the experimental data. This paper describes theexperiments and their results.