Nonsphericity of suspended marine particles and its influence on light scattering1

Nonsphericity of marine particles causes underestimation of their projected areas calculated from equivalent spherical volumes determined with volume-sensitive particle counters (e.g. Coulter Counter). A nonsphericity parameter has been defined as the ratio of the projected area averaged over all orientations of a particle to the projected area of a sphere with volume equal to that of the particle. The mean nonsphericity parameter of marine particles, determined with a scanning electron microscope, increases from about 1 for particles with a spherical equivalent diameter of 0.1 µm to about 2 for 10-µm particles. Most particles appear to be moderately nonspherical. Significant discrepancy between measured and calculated light scattering reported for suspended marine particles could be explained by underestimation with a Coulter Counter of the projected area of the particles.