Regional transport of a chemically distinctive dust: Gypsum from White Sands, New Mexico (USA)

The White Sands complex, a National Monument and adjoining Missile Range in southern New Mexico, occupies the dry bed of an ice-age lake where an active gypsum dunefield abuts erodible playa sediments. Aerosols entrained from White Sands are sometimes visible on satellite images as distinct, light-colored plumes crossing the Sacramento Mountains to the east and northeast. The IMPROVE network (Interagency Monitoring of PROtected Visual Environments) operates long-term aerosol samplers at two sites east of the Sacramento range. In recent years a spring pulse of sulfate aerosol has appeared at these sites, eclipsing the regional summer peak resulting from atmospheric reactions of sulfur dioxide emissions. A significant fraction of this spring sulfate is contributed by gypsum and other salts from White Sands, with much of the sulfur in coarse particles and concentrations of calcium and strontium above regional levels. The increase in these gypsiferous species coincides with a drought following a period of above-average precipitation. White Sands and the IMPROVE samplers together provide a natural laboratory: a climatically sensitive dust source that is both well characterized and chemically distinct from its surroundings, with a signature that remains identifiable at long-term observatories 100–200 km downwind

The assessment of a method for measurements and lead quantification in air particulate matter using total reflection X-ray fluorescence spectrometers

This paper presents the assessment of a direct method to measure and analyse Pb in air particulate matter (PM) collected on polytetrafluoroethylene (PTFE) filtering membranes prepared by the SMART STORE® procedure. The suitability of grazing incidence X-ray fluorescence technique is verified on a set of continuous and conformal thin film samples created by atomic layer deposition. Different scans changing the angles of incidence are performed and the fluorescence intensity of thin films on PTFE substrate compared with that obtained by similar thin films deposited on Si wafer substrates. The effects of sample preparation, constraints, and limitations of the experimental setup are discussed. The results obtained by three commercial total reflection X-ray fluorescence spectrometers, equipped with Mo or Rh X-ray tubes, are compared. Reference samples with different Pb content are used to define the best measurement conditions, corresponding to the maximum fluorescence intensity. The precision is evaluated in terms of relative standard deviation of the net intensity, taking into account the homogeneity of the PM samples and hardware contributions to the errors. The calibration curves are built on the basis of mono- and multi-elemental Pb loaded PTFE reference samples. The analytical parameters, namely linear calibration and determination range, limits of detection, and quantification, are determined