Observations on the magnetic iron oxide content of particulate matter in the Sahel

Abstract

Atmospheric dust influences many processes throughout the biosphere, hydrosphere, and atmosphere, most notably the climate, marine productivity, and human health. Recognizing the physicochemical characteristics of dust particulates will assist with monitoring the changes brought on by dust storms, as well as changes that may occur if dust subsides. Munsell soil color analysis was used to identify the degree of weathering at sample collection sites from the Sahel, a climate-sensitive region of North Africa. Scanning electron microscopy and energy dispersive x-ray spectroscopy were used to obtain the size, shape, and elemental makeup of individual magnetic metal particulates. Samples examined were collected along a west-east transect through Niger and Chad. No trends were found along the transect for soil color, particle physicochemistry, degree of weathering, or amount of precipitation of new minerals. Among the particles were iron oxides, iron-titanium oxides, and titanium oxides that exhibited weathering and precipitation features expected of the sample area. Several grains showed both dissolution and precipitation at the same time, indicating a variable and sensitive environment. Several contaminants were found, implicating anthropogenic sources such as mining and road dust.