Michael Darzi

Elemental analysis of soluble and insoluble fractions of rain and surface waters by particle-induced x-ray emission

H A procedure has been developed and tested for the analysis of small water samples, using particle-induced X-ray emission (PIXE) for soluble and insoluble elemental constituents separated by Nuclepore filtration. Nanogram sensitivity for samples in the 0.17-cm2 target area of a Van de Graaff accelerator proton beam permits the simultaneous determination of -15 elements from A1 to Pb in the solids on a filter and by evaporation of a few milliliters of water on thin Mylar film. Rainwater from Tallahassee, FL, contained Al, Si, Ti, and Cr exclusively in the insoluble fraction while S, K, Ca, Ni, Cu, Zn, and Br were present principally as soluble elements. Fe and P b were more evenly distributed between the two fractions. Surface-water samples in the Tallahassee area, from a lake and rainfall runoff from two shopping centers, showed qualitatively similar partitioning of the elements between the two fractions, although with a tendency for greater proportions to be insoluble.

Short term effect of rainfall on elemental composition and size distribution of aerosols in north Florida

Abstract Aerosol and rain samples were collected during winter 1978–1979 in Tallahassee, Florida and analyzed by particle induced X-ray emission (PIXE) to determine 12–15 elements from Al to Pb. The aerosol sampling was carried out before, during, and after rainfall episodes using time sequence filter samplers (streakers) and cascade impactors to investigate the variation of aerosol composition with rainfall. Al, Si, Ca, Fe, Mn, and Cl, predominantly large particle aerosol constituents (> 1 μm), were strongly affected by rain, their before/during rainfall concentration ratio being greater than 4, whereas K, Zn, Br, Pb and S, predominantly in small particle fractions ( Al, Si, Mn > Ca > Fe > K > S, Pb, Zn, Br. Differences in the speed of recovery after rain for elements, to their before rainfall values were also observed. The recovery of soil-derived elements such as Al, Si, Fe, and Mn was delayed, probably because of the wetting of the soil by rain, while S, Zn, Pb, and Br, emitted from anthropogenic sources, recovered more rapidly. The enrichments (fractionation factors) in rain of Ca, K, Zn, Cu, S, Br, and Pb normalized to Fe, relative to particulate matter in the air, were 13, 7.0, 4.3, 3.4, 2.9, 0.96, and 0.36, respectively. High enrichments of K, Zn, Cu, and S suggest that these elements might be at relatively greater concentrations than Fe at higher altitudes and be transported from more distant sources, since their apparent extent of removal is less near ground level compared to soil derived elements.

Nonurban aerosol composition near Beijing, China

Abstract The urban aerosol plume of Beijing has been sampled as a function of particle size and time at a site 110 km NE of the city, 9–16 March 1980, during the season for space heating by coal combustion. A fine particle mode, contained mostly in the 0.5–2 μm aerodynamic diameter range, could be distinguished from a coarse mode of dust having terrestial composition by reference to the size distribution of Ca. Elemental composition determined by PIXE analysis for 17 elements, including S and heavy metals, indicates fine mode concentrations higher than background aerosol but with a similarity to cleaner air with respect to both relative elemental abundances and elemental particle size distributions. The results indicate that elements contained in aged coal combustion aerosol occur mainly in 0.5–2 μMAD particles, not smaller, and the aerosol is not substantially different from background aerosol except in overall concentrations. This result may simplify the prediction of the impact of coal combustion on air quality. The results also hint that the background aerosol in more remote continental areas may also be combustion derived.

Examining several Southern Ocean data sets

The Southern Hemisphere ocean covers approximately 45% of the Earths surface and poses a major scientific challenge to initiatives such as the World Ocean Circulation Experiment (WOCE) and the Joint Global Ocean Flux Study (JGOFS) programs, whose goals include elucidation of its deep circulation and its contributions to global bio-geochemical budgets. The Southern Ocean is generally regarded as the region south of about 30°S and, in many respects, is quite different from its northern counterpart. Unlike the oceanic and atmospheric flows in the Northern Hemisphere, the Circumpolar Current “Nowlin and Klinck, 1986” and surface winds have relatively unobstructed circulations around Antarctica that allow the exchange of water between basins and result in the most intense wind forcing in the global ocean. An analysis of the annual cycle of sea level using Geosat altimetry has shown that seasonal changes in the surface ocean circulation are much weaker in the Southern Hemisphere than in the Northern Hemisphere. Also, comparison of the pigment fields obtained from the Nimbus-7/Coastal Zone Color Scanner (CZCS) indicates that the biology of the northern and southern oceans is quite different in that the northern oceans exhibit a pronounced spring bloom, while the Southern Ocean is relatively constant the year round “Esaias et al., 1986; Feldman et al. 1989”. The cause of this dissimilarity is a topic of some debate, with various arguments focusing on differences in trace nutrient supply, physical forcing, and illumination.

Fumarolic aerosols from Kilauea volcano, Hawaii

Abstract As part of a geochemical survey of Kilauea, an active Hawaiian volcano, aerosol samples were collected in February 1979, a quiescent period, from several fumaroles within the caldera and along border faults. Measurements of gaseous emissions and physical parameters were also made by volcanologists from the French Centre Nationale de Recherche Scientifique and the U.S. Geological Survey. Portable and self-contained equipment, including pumps, batteries and cascade impactors, was used for the aerosol collection. Results are reported here for 16 samples analyzed at the Florida State University using particle induced X-ray emission for a dozen or more elements including Si, P, S, Cl, and Fe. These analyses are among the first for size fractionated particles from volcanic activity. The six size fractions (from 8.0 μm particle diameter) collected by single orifice cascade impactors enable differentiation to be made between primary aerosols converted from gases and reentrained particles from the ground that are swept into the plume.

Sampling method and pine analysis for atmospheric sulfur dioxide with alkali coated filters

Abstract Nuclepore filters coated with an alkaline solution were used for collection of sulfur dioxide in the air. The best alkaline solution for the coating was 20% potassium hydroxide with 10% glycerol or triethanolamine. 25 mm diameter Nuclepore filters could be coated by simple procedures with potassium hydroxide, with about 10% error, and the average coated amount of potassium hydroxide was 125 μg for a filter. The collection efficiencies of the coated filter for sulfur dioxide concentration, flow rate, and loading were examined using known concentrations of sulfur dioxide. A collection efficiency of more than 98% was observed below 4.0 1/min flow rate (19 cm/s air velocity) at 0.054 ppm sulfur dioxide, 25°C and 30% r.h. The capacity for the coated filter was 50% loading, equivalent to μg sulfur dioxide, and higher loadings caused lower collection efficiencies. Sulfur dioxide collected on the coated filters was directly analyzed by particle induced X-ray emission (PIXE) using 5 MeV protons, which has high sensitivity at nanogram levels, and the results of PIXE analysis of sulfur dioxide agreed well with the West Gaeke method. The coated filter and PIXE analysis were used for measurements of sulfur dioxide at the coast and ocean in north Florida, a relatively unpolluted area, during February 1979. Their average concentration was 1.3 ppb (n = 13).

The problem of aliasing in inferring long-range air pollution transport to Mauna Loa, Hawaii

Choice of sampling strategy or criteria for selection of aerosol concentration data from a time series record can lead to errors in estimating periodic regularities because of aliasing. By means of an example from Mauna Loa Observatory during spring dust transport from Asia, it is shown that the detection of possible transport of pollution S across the Pacific to Hawaii could be missed through inadvertent aliasing errors.