Mineral Aerosol Particles Research Articles

Atmospheric trace elements over source regions for Chinese dust: concentrations, sources and atmospheric deposition on the Loess plateau

The mass-particle size distributions of up to 17 trace elements in aerosol particle samples from dust storm and non-dust storm periods were determined for three sites in or near the source regions of Chinese dust. The mass of particulate material in the atmosphere at the sites is dominated by mineral aerosol particles. An absolute principal component analysis of the non-dust storm elemental data for the loess region allows the estimation of the mass contributions from two coarse-particle classes (soil dust and dust associated with pollutants), and two fine-particle classes (soil dust and anomalously enriched). For most elements (Al, Si, Ca, Fe, Ti, K, S and As), the mass-particle size distributions (MSDs) were approximately log-normal. The mass-median diameters (MMDs) of the soil-derived elements tended to decrease with distance from the desert region and when the dust storms subsided. Total dry deposition velocities were calculated by fitting a log-normal distribution to the aerosol data and calculating deposition rates for 100 particle-size intervals using a two-layer deposition model. The mean dry-deposition rates and fluxes were highest during dust storms over desert regions. In thloess region, the calculated dry deposition velocities of soil derived elements (Al, Si, Ca, Fe and Ti) during non-dust storm periods were from 3.1 to 3.7 cm s −1. From the estimated mass-particles size distributions, the coarser and finer mineral particles were found to benriched with Ca, Fe, Ti and K relative to Al or Si. On a yearly basis, the dry atmospheric input to the Loess Plateau was mainly attributable to normal transport processes, i.e. non-dust storm conditions. Wet deposition fluxes estimated from scavenging ratios indicate that dry deposition dominated the total atmospheric deposition of mineral aerosol. The deposition of aerosol particles associated with coal burning or other anthropogenic sources also was considerable on the Loess Plateau.

The adsorption of dissolved iron on marine aerosol particles in surface waters of the open ocean

The adsorption of dissolved iron in seawater onto marine aerosol particles, illite, and Chinese loess, using 59Fe as a tracer, showed the following points. (1) The adsorption capacity of mineral aerosol particles for dissolved iron could be > 27 nmol mg −1. Even if the dissolved iron, D(Fe), were ∼ 7 nmol kg −1 (∼ 14–100 times D(Fe) in the surface seawater of the North Pacific), the saturated adsorption capacity of the mineral aerosol particles would not be reached. (2) The concentration of suspended particles appears to be the prime variable controlling the adsorbed fraction of iron. Most dissolved iron may be adsorbed onto particles in the ocean surface microlayer, especially on the organic coating of the aerosol particles. This may explain why the dissolved iron concentration in the open ocean is much lower than the apparent “saturated” concentration of iron(III). (3) The adsorption capacity of mineral aerosols was over twice that of illite and Chinese loess. (4) Although adsorption is the predominant mechanism controlling D(Fe) in the open ocean, the addition of mineral aerosol particles to the open ocean would result in a net addition of dissolved atmospheric iron in seawater.

Concentrations, sources, and fluxes of trace elements in the remote marine atmosphere of New Zealand

The concentrations of trace elements were determined for aerosol particle, dry deposition, and precipitation samples collected from Ninety Mile Beach on the North Island of New Zealand. Major objectives for the studies, which were conducted as part of the SEAREX (Sea/Air Exchange) Program, were to investigate the concentrations, sources and geochemical cycling of trace elements in the westerly wind field over the South Pacific Ocean. Many of the trace elements were associated with natural materials such as atmospheric sea salt or mineral aerosol. The mean concentration of atmospheric sea salt (∼7.9 μg m −3) was 5 to 30% higher than that predicted by models based on relationships between salt concentrations and wind speed. Mineral aerosol particles were transported through the atmosphere from Australia, and the concentration of atmospheric dust (∼200 ng m −3) was lower than the expected long‐term average due to the fact that the sampling at Ninety Mile Beach was conducted during the climatological low‐dust season. Estimates of the atmospheric deposition rates suggest that eolian material constitutes a significant fraction of the nonbiogenic deep‐sea sediments of the region. Certain trace elements, including Ag, Cd, Cu, I, Mo, Pb, Sb, Se, Ni, and Zn, were enriched over the concentrations expected from natural sources. Anthropogenic emissions from Australia and New Zealand evidently affected the concentrations of several of these elements on local to regional scales.

Non-steady-state biological removal of atmospheric particles from Mediterranean surface waters

IT has recently been suggested that the deposition of mineral aerosol particles, primarily transported from Africa during sporadic but intense events1,2, may have a profound influence on the geochemistry and the sedimentology of the Mediterranean Sea1-3. Several studies in the open ocean4-7 have shown that such particles, with radii generally less than 5 μm, are removed from the surface waters within a few weeks, together with large organic particles produced by biological packaging7. Here we report data from time-series measurements of both atmospheric inputs and water-column participate fluxes at 200m depth obtained from sediment traps, which show that such a biological control also prevails in northwestern Mediterranean waters. On short time-scales, concentrations and fluxes in the upper water column can increase significantly following dust transport and deposition events, with a response time of the order of one week. Such non-steady-state behaviour must be taken into account when assessing the impact of pulsed atmospheric inputs on particulate trace element concentrations and fluxes in the water column.

Seasonal variability of the elemental composition of atmospheric aerosol particles over the northwestern Mediterranean

Beginning in 1985, a continuous aerosol sampling program has been undertaken at a coastal location in northwestern Corsica. This site is 300 m above sea-level and at least 20 km from local pollution sources. It is exposed during 80% or more of the time to maritime air masses which have travelled over the western Mediterranean from southern, western and northern directions. Daily 24-h aerosol samples were collected on 0.4 μm pore size nuclepore filters from a 10 m high tower and analysed for Al, Si, P, S, K, Ca, Ti, Mn, Fe and Zn by X-ray fluorescence, and for Na, Cu and Pb by flameless atomic absorption. The data obtained up to now, from April 1985 to April 1986, show that the temporal variability of the concentrations displays 2 distinctive patterns. First, a seasonal pattern is observed for the elements of continental origin, either natural (e.g., Al, Si) or anthropogenic (e.g., S, Pb). This pattern is inversely related to the frequency and amount of rainfall such that the highest concentrations are observed between May and October. Estimates based on these data indicate an average time of 2 days to reload that atmospheric environment with aerosol particles from continental sources. This seasonal pattern is not observed for locally produced sea-salt aerosol particles (index Na), whose concentration is related to local wind speed. Elements associated with mineral aerosol particles exhibit sporadic but intense concentration peaks that are superimposed on this general pattern. 20 of these events were recorded for the sampling period considered with their frequency being maximal in spring and summer. 3-D air-mass trajectories show that all these events are associated with transport of soil dust from Africa. DOI: 10.1111/j.1600-0889.1989.tb00314.x

Atmospheric input of trace metals to the western Mediterranean: uncertainties in modelling dry deposition from cascade impactor data

The mass-particle size distributions (MSDs) of Na, Al, Cd, and Pb were determined from 17, 1–5 day, high-volume cascade impactor samples collected throughout the Western Mediterranean atmosphere between 1980 and 1983. As expected, the mass median diameter (MMD) was the largest for Na, representative of sea-salt aerosol, with a median value of 5.9 μm. The median value for the MMD for Al, representative of mineral aerosol, was 2.8 μm. The smallest values of the MMD were found for pollution-derived elements, Cd and Pb: 0.7 μm. In most cases, the MSDs, for each of the elements, were log-normal. Total dry deposition velocities were calculated from the two-layer deposition model of Slinn and Slinn (1980) using three approaches: (i) by characterizing the distribution as a MMD, (ii) by considering the size distribution as directly given by the cascade impactor, (iii) by fitting the assumed log-normal distribution and dividing it into 100 successive intervals. The first approach appeared to give underestimates. The two other approaches yielded similar results for Cd and Pb, of the order of 0.05 cms -1 . For these elements, however, more than 20% of the total dry deposition flux was due to particles with diameters of 7.2 μm or greater (collected by impactor stage 1). For Na and Al, the third approach yielded values at least one order of magnitude higher than when using the two others. This clearly underlines the major role played by large particles in controlling the dry deposition of sea-salt and mineral aerosol particles. Direct measurements of Al dry deposition, made in 1985–1986 on the northwestern coast of Corsica, agree best with the values predicted by the third approach (mean calculated and measured values of 1.8 and 3.0 cm s -1 respectively). Scanning electron microscopy examinations of samples confirm that mineral aerosol particles with diameters of 10 μm or greater dominate the dry deposition flux. Preliminary data indicate that for mineral aerosol particles, this flux is, on a yearly basis, about half of the wet deposition flux. However cascade impactor data are not adequate to retrieve true mass-particle size distribution in the size range which controls dry deposition ( D > 7 μm), and this is shown to be the source for one order of magnitude uncertainties in dry deposition calculations. DOI: 10.1111/j.1600-0889.1989.tb00315.x

Study of continental material transported through the atmosphere to the oeean

I am deeply honored to have been selected as a recipient of the 1987 Okada Prize by the Oceanographical Society of Japan. The present paper reviews my work and recent studies of other investigators concerning mineral aerosol (dust) particles in the marine atmosphere over the Pacific Ocean. I would like to emphasize the importance of atmospheric deposition of continental substances to the ocean environment.

Dry deposition models and the air/sea exchange of trace elements

Dry deposition rates of representative trace elements were calculated from measured mass‐particle size distributions and two deposition models (Slinn and Slinn, 1980; Williams, 1982). The aim of the study was to investigate how deposition rates were affected by (1) differences in transfer velocities to smooth and broken water surfaces, (2) wind speed, and (3) relative humidity. Comparisons of the dry deposition rates that were calculated for sodium and aluminum suggest that surface waves do not greatly affect the dry deposition rates of sea‐salt or mineral aerosol particles, respectively. In contrast, the deposition rate for 210Pb was as much as 5 times higher when a term was included to account for the effects of broken water surfaces. These results suggest that the air/sea exchange of a substance whose mass is predominately associated with small particles may be significantly enhanced by deposition to broken water surfaces.

Atmospheric trace elements at Enewetak Atoll: 1. Concentrations, sources, and temporal variability

The concentrations of 29 elements were measured in aerosol particles collected in 1979 during SEAREX experiments at Enewetak Atoll (11°N, 162°E) in the tropical North Pacific. The concentrations of Na, Mg, Cl, K, Ca, and Br were dominated by marine sources; these elements had similar mass‐size distributions, and their atmospheric concentration ratios (normalized to Na) were similar to the corresponding ratios in bulk seawater. Atmospheric inputs of aluminosilicate particles from crustal weathering controlled the aerosol particle concentrations of Al, Sc, Mn, Fe, Co, Cs, Ba, Ce, Eu, Hf, Ta, and Th. Mean concentrations of these crustally derived elements decreased by an average of 91% (±4.1%) from the local dry season (April to May) to the wet season (July to August); this general decrease was attributed to the abatement of dust storms in Asia. At times the influx of dust from Asia dominated the concentrations of V, Cr, Rb, and Cu in aerosol particles, but when dust concentrations decreased, noncrustal sources for these elements became apparent. A fourth group of elements (Zn, Se, Ag, Cd, Sb, I, and Pb) exhibited average, atmospheric concentrations that were higher than those expected from the flux of sea salt or the dispersal of mineral aerosol particles. Enrichments of these trace elements relative to average crustal material increased as the atmospheric dust concentrations subsided. Supplement is available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, D.C. 20009. Document C83‐001; $2.50. Payment must accompany order.

The sources of sulfate, vanadium and mineral matter in aerosol particles over Bermunda

Seventy-eight atmospheric particle samples were collected from April to October, 1974, at Bermuda and were analyzed for V, Al, Mn, Na, Cl and SO 2− 4. The chemical composition of aerosol particles at Bermuda is significantly affected by pollution sources in continental regions. Most of the sulfate in excess of that from sea spray and V in excess of that from weathered crustal material in the particles at Bermuda is pollution derived, primarily from North America. Relatively direct transport of aerosol particles from North America to Bermuda apparently occurs 35–40 % of the time each year. Significant quantities of mineral aerosol particles are also transported to Bermuda from North America under these conditions. Even greater quantities of mineral aerosol particles are transported to Bermuda from North Africa. Transport to Bermuda from this region in the eastern North Atlantic occurs 40–45 per cent of the time each year. Under these conditions pollution derived components in the marine aerosol at Bermuda are considerably reduced.