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United States Department of Agriculture

Agricultural Research Service

Title: A Two-Parameter Weibull Function to Describe Airborne Dust Particle Size Distributions of the Southern High Plains, Usa

Authors
item ZOBECK, TEDDY
item Gill, Thomas - TEXAS TECH UNIVERSITY
item Popham, Thomas

Submitted to: Earth Surface Processes and Landforms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 23, 1999
Publication Date: N/A

Interpretive Summary: Recent concern for the health and climatic impact of airborne dust has produced increased interest in this subject. Efforts are now underway to develop equipment and methods to analyze airborne dust properties in order to relate the dust properties to the source of the dust. Knowledge of the dust source will facilitate development of sound strategies to reduce air pollution from blowing dust. In this study we relate dust properties to th physical and chemical properties of the dust source. As clay content increased and sand content decreased, the total amount of suspended dust increased. We also compared the amount of dust generated from dirt road samples with samples from field soils. Dirt roads produce about twice the amount of airborne dust as agricultural fields. We also described the distribution of particles in the dust using a well-known mathematical formula and showed the same formula can be used to describe the distribution of dust from a wide variety of dust sources.

Technical Abstract: A number of mathematical distributions have been proposed for the description of the particle size distribution of unconsolidated sediments. However, few studies have mathematically described aeolian dust particle size distributions. We test the hypothesis that the Weibull distribution may be used to describe airborne soil grains. Surface samples were collected from 52 sites including soils, dirt roads and roadside ditches i the Southern High Plains of west Texas. The samples were tumbled in the Lubbock dust generation, sampling and analysis system to generate a dust cloud. The particle size distribution of the dust was measured in situ by laser diffraction and PM10 concentration was determined gravimetrically. This study demonstrated that the Weibull cumulative distribution function (CDF) is an excellent choice to describe the particle size distribution of dust suspended from mineral sediment. A Weibull cdf, used to describe the dust cloud size distribution, accounted for 94% of the variation in estimates of particles less than or equal to 50 um diameter. The fraction of particles less than or equal to 10 um was correlated with properties of the sediment from which the airborne dust was derived. As clay content increased, the total amount of suspended dust increased and the fraction of suspended less than or equal to 10 um particles in the dust cloud decreased. Analyses of variance showed no significant differences (P<0.05) among sampling locations (roads, vs ditches vs soils) for cumulative fraction values for 2.5, 10, 25, 30, 50 um particles. However, the PM10 concentration values were significantly different among locations. The road samples produced about twice the amount of PM10 (490 mg m3) as the soil or ditch samples (235 mg m3).

Last Modified: 7/25/2014
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