Mineral Dust Concentrations Research Articles

Origins of African dust transported over the northeastern tropical Atlantic

On the basis of 3 years of daily measurements of mineral dust concentrations at Sal Island (Cape Verde), this study focuses on the origin of the dust transported over the northeastern tropical Atlantic during the dusty season (October to April). Using backward trajectories, we have identified three different sectors of origin of the transported dust, covering the Sahara (north/west and central/south) and the Sahel regions. Time variations of the dust transport from these different areas can be explained by the seasonal shift of the subtropical high‐pressure center. A geochemical approach highlights that the calcium amount and the Si/Al ratio of the transported dust differ according to these source regions, in relation to their respective soil compositions.

An additional low layer transport of Sahelian and Saharan dust over the north‐eastern Tropical Atlantic

Mineral dust concentrations have been measured from a monitoring aerosol station set up at Sal, Cape Verde Island between December 1991 and December 1994 in order to assess the transport process of African dust over the North‐eastern Tropical Atlantic. These measurements indicate a pronounced seasonal pattern, with maximum dust concentrations observed during winter. A meteorological analysis shows that the transport of dust occurs at low altitudes, in the trade winds layer, during this season. Large quantities of dust are carried out of North‐western Africa, in particular from the Sahel at these altitudes. Such process could constitute the major supply of atmospheric mineral matter to the surface sea water of the Eastern Atlantic.

Trace elements in the atmosphere over the North Atlantic

The concentrations of trace elements in aerosol particles from the atmosphere over the North Atlantic Ocean were determined as part of a program designed to characterize the chemical climatology of the region. For these studies, which were part of the Atmosphere‐Ocean Chemistry Experiment (AEROCE), 2 years of samples were collected at Tudor Hill, Bermuda (BTT), and at Ragged Point, Barbados (BAT); and 1 year of samples was collected at Mace Head, Ireland (MHT) and at the Izaña Observatory, Tenerife, Canary Islands (IZT). One major component of the aerosol was atmospheric dust, and the ranking for the median mineral dust concentrations as represented by aluminum was BAT > IZT > BTT > MHT. The Al concentrations at BAT, IZT, and BTT ranged over 4 orders of magnitude, i.e., from 0.001 to 10 μg m−3. At MHT the maximum dust concentrations were about a factor of 10 lower than at the other sites, but the lower end of the range in dust concentrations was similar at all sites. The mineral dust concentrations generally were highest in summer, and the flux of atmospheric dust was dominated by sources in North Africa. The elements showing clear enrichments over the concentrations expected from sea salt or crustal sources were I, Sb, Se, V, and Zn. At Izaña, which is in the free troposphere (elevation ∼2360 m), the concentrations of Se and I were much lower than at the boundary layer sites; this difference between sites most likely results from the marine emissions of these elements. The impact of pollution sources on trace element concentrations was evident at all sites but varied with season and location. The concentrations of elements originating from pollution sources generally were low at Barbados. Analyses of trace element ratios indicate that there are large‐scale differences in the pollution emissions from North America versus those from Europe and Africa. Emissions from pyrometallurgical industries, steel and iron manufacturing, and possibly biomass burning are more evident in the atmospheric samples influenced by transport from Europe and Africa.

The use of tracer gases to determine dust dispersion patterns and ventilation parameters in a mineral processing plant.

A study was conducted in a fluorspar milling plant to assess the effectiveness of tracer gases as a reliable supplement to conventional air-monitoring and ventilation measurements. In the course of this study, a tracer gas was used as a surrogate substance to analyze the direction and the rate of spread of contaminants from various potential dust production points in the plant. Time-weighted average and continuous mineral dust concentrations were measured in several areas of the plant; these results were compared and correlated with steady-state tracer gas concentrations in the mill. Time-weighted average dust concentrations varied between 0.18 and 0.57 mg/m3 for total dust and 0.04 and 0.20 mg/m3 for quartz respirable dust, depending on the location. Correlation of these values with steady-state tracer gas concentrations yielded linear relationships with correlation coefficients (R2) of 0.95 and 0.87, respectively, for total and quartz dust. Results from this study, therefore, indicate that tracer gases may help model the spread of airborne respirable dust from point sources. These tracer gas releases also allowed the simultaneous quantitative determination of air residence times and contaminant clearance times from the building. Hence, tracer gases will help industrial hygienists obtain useful data with respect to building ventilation.

The distributions of particulate atmospheric trace metals and mineral aerosols over the Indian Ocean

Abstract Data are presented for the concentrations of Al, Fe, Mn, Ni, Co, Cr, V, Cu, Zn, Pb and Cd in aerosols collected over two contrasting regions of the Indian Ocean. These are: (1) the northern Arabian Sea (AS), from which samples were collected in the northeast monsoon, during which the region receives an input of crustal material from the surrounding arid land masses; and (2) the Tropical Southern Indian Ocean (TSIO), a remote region from which samples were collected from air masses for which there were no large-scale up-wind continental aerosol sources. The TSIO samples can be divided into two populations: Population I aerosols, collected from air masses which have probably impinged on Madagascar, and Population II aerosols, which have been confined to open-ocean regions to the south of the area. The data indicate that there are strong latitudinal variations in the chemical signatures of aerosols over the Indian Ocean. The input of crustal material to the Arabian Sea gives rise to an average Al concentration of about 1000 ng m −3 of air in the northeast monsoon regime. As a result, the concentrations of all trace metals are relatively high, and the values of crustal enrichment factors are less than 10 for most metals, in the AS aerosols. In contrast, TSIO Population II ‘open-ocean southern air’ sampled during the southwest monsoon season, has an average Al concentration of only about 10 ng m −3 of air. Trace metal concentrations in the TSIO ‘open-ocean southern air’ during the southwest monsoon season are representative of ‘clean’ remote marine air and are generally similar to those reported over the central North Pacific. Mineral dust concentrations over the Indian Ocean decrease in a north to south direction, from about 15–20 μg m −3 of air in the extreme north to about 0.01–0.25 μg m −3 of air in the far south. The deposition of mineral dust over the northern Arabian Sea can account for approximately 75% of the non-carbonate material incorporated into the underlying sediments. In the Arabian Sea the dissolved atmospheric inputs of all the trace metals, with the exception of Cu and Co, exceed those from fluvial run-off by factors which range from 9.6 for Pb to 1.6 for Cr.

Meteorological analysis of long range transport of mineral aerosols over the North Pacific

Meteorological data are used to investigate the importance of source, transport, and removal factors in the temporal and areal variation of mineral dust concentrations observed in the SEAREX (Sea/Air Exchange Program) Network of aerosol sampling stations over the open Pacific Ocean. Earlier studies established that Asian desert dust is carried out over the ocean by the mid‐latitude westerlies and may be present over the entire North Pacific area. A 6‐year climatology of routine surface meteorological reports of dust in Asia is used to examine the broad maximum in mineral dust concentrations in the months February‐May observed at all the North Pacific sites. The gross features of this seasonal variation are controlled by the occurrence and areal extent of dust outbreaks. Secondary peaks in the frequency of dust storms, in October‐December, correspond to isolated peaks in the dust concentration at the sites closest to the mid‐latitudes. Isentropic trajectory analyses are presented for individual events of peak concentrations supporting earlier indications that the dust transport begins at high elevations over the arid regions and gradually subsides for those parcels which move toward the south. The average transport path for high concentration periods, obtained by superposing trajectory patterns for events over a 6‐year period, is shown to explain the latitudinal variation in the concentrations. Removal by local orographic showers at Oahu is shown to be unimportant, while removal by the intense tropical rainfall near Fanning Island is shown to be a dominant influence on the seasonal variation of concentrations there. Rainfall data at the remote Pacific sites indicate that the 1981–1986 period was generally representative, despite the strong El Niño/Southern Oscillation event which occurred in 1982–1983.

Seasonal and areal variation of continental aerosol in the surface air over the western North Pacific region

Weekly aerosol samples were collected for two years from 1981 at six stations in the western North Pacific region. The samples were analyzed for aluminum to determine the mineral dust concentration in the air. By combining our data with observations in the central and eastern North Pacific by a US research group, the following results and conclusions have been obtained. Spring peaks in atmospheric mineral dust were observed at all the stations accompanied byKosa episodes (hazes due to mineral dust of Chinese origin). The spring peaks, however, varied from year to year. The mean concentration of mineral dust depends not only on the distance from the Asian coast but also on the latitude of the sampling station. The half-decrease distance of the atmospheric mineral dust turned out to be 500–600 km for all latitudes in the western North Pacific. This indicates that the rate of deposition of mineral dust in the western North Pacific is much larger than that in the central and eastern North Pacific.

Pollen-Analysis Investigation of a 20 m. Firn Pit on the Kesselwandferner (Ötztal Alps)

AbstractFirn samples from a 20 m. deep pit were examined by pollen analysis methods in order to confirm the stratigraphy of the annual net accumulation back to 1949. The late summer horizon separates the overlying winter layer with a small pollen content from a firn layer with a large pollen content. There are also differences in the spectra of the species which enable a seasonal separation of the layers. In addition, the mineral dust content was examined.

Pollen-Analysis Investigation of a 20 m. Firn Pit on the Kesselwandferner (Ötztal Alps)

AbstractFirn samples from a 20 m. deep pit were examined by pollen analysis methods in order to confirm the stratigraphy of the annual net accumulation back to 1949. The late summer horizon separates the overlying winter layer with a small pollen content from a firn layer with a large pollen content. There are also differences in the spectra of the species which enable a seasonal separation of the layers. In addition, the mineral dust content was examined.