A diagram has been developed to demonstrate the response of the beam attenuation coefficient per unit volume (termed the specific beam attenuation coefficient) to changes in particulate size distribution and refractive index. Upon examination, the diagram accurately predicts the optical behavior of particulate samples measured by previous researchers. With estimates of the particle refractive index and size distribution, the diagram provides a higher degree of resolution than was previously assumed in using light transmission measurement to determine the volume of suspended particulate matter.