Study of Black Sand Particles from Sand Dunes in Badr, Saudi Arabia Using Electron Microscopy

Particulate air pollution is a health concern. This study determines the microscopic make-up of different varieties of sand particles collected at a sand dune site in Badr, Saudi Arabia in 2012. Three categories of sand were studied: black sand, white sand, and volcanic sand. The study used multiple high resolution electron microscopies to study the morphologies, emission source types, size, and elemental composition of the particles, and to evaluate the presence of surface “coatings or contaminants” deposited or transported by the black sand particles. White sand was comprised of natural coarse particles linked to wind-blown releases from crustal surfaces, weathering of igneous/metamorphic rock sources, and volcanic activities. Black sand particles exhibited different morphologies and microstructures (surface roughness) compared with the white sand and volcanic sand. Morphological Scanning Electron Microscopy (SEM) and Laser Scanning Microscopy (LSM) analyses revealed that the black sand contained fine and ultrafine particles (50 to 500 nm ranges) and was strongly magnetic, indicating the mineral magnetite or elemental iron. Aqueous extracts of black sands were acidic (pH = 5.0). Fe, C, O, Ti, Si, V, and S dominated the composition of black sand. Results suggest that carbon and other contaminant fine particles were produced by fossil-fuel combustion and industrial emissions in heavily industrialized areas of Haifa and Yanbu, and transported as cloud condensation nuclei to Douf Mountain. The suite of techniques used in this study has yielded an in-depth characterization of sand particles. Such information will be needed in future environmental, toxicological, epidemiological, and source apportionment studies

Response time curves of ion-selective electrodes

The response characteristics of different types of ion-selective electrodes were investigated thoroughly for obtaining kinetic information for the electrode response. On the basis of response time data or supposed electrode mechanisms, the ion-selective electrodes have been divided into different groups. For the evaluation of the response time curves of electrodes, at which the rate-determining step is the diffusion of the appropriate ion in the electrode membrane phase (neutral carrier-, and covered surface electrodes), a diffusion model has been used. The response characteristics of electrodes operating on ion-exchange equilibria (e.g., precipitate based electrodes etc.) have been interpreted with the help of a first-order kinetic equation. In addition to this, a so-called multielectrode model has been worked out for the general interpretation of the electrode response if the rate determining sequence of the overall potential determining step is covered by a diffusion process through the adhering laminary layer at the electrode surface. © 1976, American Chemical Society. All rights reserved