The Relation Between Visibility and the Size-Number Distribution of Airborne Soil Particles

E. M. Patterson National Center for Atmospheric Research, Boulder, Colo. 80303

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D. A. Gillette National Center for Atmospheric Research, Boulder, Colo. 80303

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G. W. Grams National Center for Atmospheric Research, Boulder, Colo. 80303

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Abstract

Simultaneous visibility observations and size-number distribution measurements of airborne soil particles were made during incidents of soil erosion in west Texas. Visibilities were calculated by applying Mie scattering theory to measured size distributions and were compared with observed visibilities. Agreement was found, and similar comparison with artifical modicications to the observed size distributions demonstrated that any major changes in the observed size distributions would result in significant discrepancies between the observed and the calculated visibilities. These comparisons confirm that under our experimental conditions the optically important particles are those in the size range 0.62 < r < 20 μm. The sensitivity of the calculated visibility to modifications in the measured size distribution implies that such comparisons between calculated and observed visibility provide a means of confirming size distribution measurements under a variety of conditions.

Abstract

Simultaneous visibility observations and size-number distribution measurements of airborne soil particles were made during incidents of soil erosion in west Texas. Visibilities were calculated by applying Mie scattering theory to measured size distributions and were compared with observed visibilities. Agreement was found, and similar comparison with artifical modicications to the observed size distributions demonstrated that any major changes in the observed size distributions would result in significant discrepancies between the observed and the calculated visibilities. These comparisons confirm that under our experimental conditions the optically important particles are those in the size range 0.62 < r < 20 μm. The sensitivity of the calculated visibility to modifications in the measured size distribution implies that such comparisons between calculated and observed visibility provide a means of confirming size distribution measurements under a variety of conditions.

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