Total Dust Deposition Research Articles

Æolian dust deposition rates, particle‐sizes and contributions to soils along a transect in semi‐arid New South Wales, Australia

AbstractThe entrainment, transport and deposition of æolian dust are important processes affecting soil development at the margins of deserts. To assess accurately the impact of deposited æolian dust on soil development, it is important not only to measure total dust deposition rates, but to distinguish additions of remotely and regionally sourced dust from locally derived material as well (which should not be viewed as new soil material as it is derived from æolian re‐mobilization of an existing soil). Because of the well‐established relationship between dust particle‐size and distance travelled from source, the particle‐size distribution of deposited dusts can be used to identify the distance to probable source regions, in addition to identifying matching topsoil particle populations. Three dust traps were located along a transect of semi‐arid south‐eastern Australia, to measure æolian dust deposition rates between late 2000 and late 2001. The particle‐size distributions of selected dust deposits were measured and, with the aid of meteorological data, probable dust source regions determined. Particle‐size distributions of the topsoils at each dust trap location were also measured to determine if any dust and soil particle populations matched. Although the sampling period was relatively short, and there was relatively little dust storm activity in this part of Australia during this time, a clear pattern of diminishing total dust deposition was measured downwind along the south‐east dust path. Dust deposition rates were also moderate to low by global standards. Source regions of deposited dust were interpreted as being: (i) a combination of south‐western and local sources; (ii) a combination of north‐western and local sources; and (iii) a mixed source where dust was rained‐out. The relative importance of these sources was correlated strongly with seasonal weather conditions, although the proportion of local dust in each deposit was greater at the arid (western) end of the transect. The effects of deposited dust on soil profile development are greatest at the western and central transect locations. At the western location, a fine‐grained particle population distinctive of the south‐western and north‐western regional dusts and a coarse silt‐sized particle population characteristic of local dusts, are also present in the topsoil, altering the texture of this Arenosol derived from dune sand. At the central location, where a Calcisol has formed in lacustrine lunette sediment, local dust of the same size as the dominant silt population of the topsoil continues to be deposited, while minor topsoil populations of very fine‐grained silt match regional and long‐distance dusts deposited at the site. Deposited dust appears to have been a less important soil development factor at the more humid eastern site because of the much smaller rates of dust deposition there. Nevertheless, a minor population of very fine silt particles in the Vertisol topsoil matches long‐distance dusts deposited at the site, suggesting a small input of dust to this alluvial soil. The particle‐size methodology used here has applications in other studies of dust contributions to peri‐desert soils. In particular, particle‐size distribution ‘smoothness’ may provide an indication of whether soils have simple or complex origins.

Vanadium Concentrations in Settled Outdoor Dust Particles

Atmospheric dustfall is an important aspect of urban dust studies. Vanadium is considered as the marker element of air pollution emitted from residual oil and coal combustion. In this study, vanadium levels of outdoor dust particles are determined. The studied area covers the six sites located in Adapazarí (Turkey), which represents an earthquake-hit environment. The mass deposition rate was calculated for each sampling plate over the 30-days collection periods. The deposition rates for the six places in Adapazarí ranged from 20.5 to 84.9 microg/cm2/day. The arithmetic mean deposition rate for all places was 45.3 microg/cm2/day. Total dust deposition and vanadium loadings typically increased in magnitude according to the area order: Kampus > Serdivan > Cark C. > Ozanlar > Erenler > Yeşiltepe and Kampus > Serdivan > Cark C. > Ozanlar > Erenler > Yeşiltepe, respectively. The results suggested that vanadium may be useful for assessing the level of environmental pollution.

A numerical study of the contributions of dust source regions to the global dust budget

Contributions of the nine potential dust source regions (North and South Africa, the Arabian Peninsula, Central Asia, eastern and western China, North and South America, and Australia) to the global dust budget are investigated with a global dust transport model. A six-year simulation (1990 to 1995) indicates that the greatest contributor to the global dust budget is found to be North Africa (the Sahara Desert), which accounts for 58% of the total global dust emission and 62% of the total global dust load in the atmosphere. Australian dust dominates the southern hemisphere. The dust emission and atmospheric dust load originating from East Asia (eastern and western China) are estimated to be 214 Tg yr − 1 and 1.1 Tg, respectively, which are 11% and 6% of the total global dust emission and dust load. Dust from East Asia dominates the atmospheric load over China and Mongolia (about 70%), Korea (60%), Japan (50%), and the North Pacific Ocean (40%). The contribution of dust originating from regions other than East Asia to the dust load over these East Asian countries and the North Pacific Ocean cannot be ignored. The simulated total dust deposition flux on Greenland suggests a possible overestimation of the Saharan dust and an underestimation of the East Asian dust in the Arctic region, which may be a common problem with global dust transport models. Possible reasons for the underestimation of the East Asian dust are discussed.

Harmattan dust deposition and particle size in Ghana

In Ghana, a dust-laden Harmattan wind blows from the Sahara from November to March. Some of the dust is trapped in the vegetation, in the lakes and other inland waters, while the rest is blown further away into the Ivory Coast or into the Atlantic Ocean. Several methods have been used to trap the Harmattan dust, mainly bowls with or without water, but also plates or sheets of various materials have been used. This paper compares three different methods to trap the Harmattan dust and describes the differences in amount and particle size distribution of dust trapped in various agroecological zones. The investigation shows that bowls with water trap more dust than plastic mats with 1.5 cm straw which again trap more dust than wooden plates. The bowl values can be used as a measure of the total Harmattan dust deposition, the mat values can be used as a measure of how much Harmattan dust is retained by vegetation, while the plates provide a measure of how much dust is retained on vegetation free areas. The amount of Harmattan dust captured is largest in the north, the amount of dust retained differs significantly from year to year, and a severe Harmattan in the north is not necessary coincident with severe Harmattan in the south. The dust particle size becomes finer towards the south and with increasing amounts of organic matter, and the particle size distribution shows that the major part of the dust trapped is long-term suspended material with a significant input of local dust. The dust particle size is coarser on the mats than in the bowls due to re-suspension from the mats. The presence of diatoms in the samples from Bawku indicates that a substantial part of the dust originates from former lakes in the Sahara. The amount of dust retained in the north gives a deposition rate of about 15 mm per 1000 years. This may explain why loess layers have not developed in Ghana.

Effect of rock fragment embedding on the aeolian deposition of dust on stone‐covered surfaces

AbstractMany stone‐covered surfaces on Earth are subject to aeolian deposition of atmospheric dust. This study investigates how the deposition of dust is affected when rock fragments become gradually more embedded in the ground or, inversely, become more concentrated on the surface. Experiments were executed in an aeolian dust wind tunnel with eight different types of pebbles. The following parameters were measured: dust deposition on the pebbles, dust deposition between and underneath pebbles, total dust deposition (pebbles + inter‐pebble space), and the fraction, of total deposition, of dust caught by the pebbles alone. The absolute amount of dust deposition and the dust deposition density (dust deposition per unit surface) were studied for each parameter. The effects exerted by pebble size, pebble flattening, pebble elongation and wind speed were also investigated. Dust patterns on and around pebbles were also studied via flow visualization.The absolute amount of dust settling on pebbles decreases the more that the pebbles become embedded. Dust deposition density on pebbles, on the other hand, increases with embedding. The more pebbles become embedded in the soil, the more efficient the process of dust deposition on pebbles becomes. Dust deposition between and underneath pebbles increases with pebble embedding. Dust deposition density between and underneath pebbles is maximum at 50 per cent embedding, showing that in this area dust deposition is most efficient when pebbles are halfway embedded. Total deposition slightly decreases the more pebbles become embedded, but total dust deposition density increases with embedding.Aerodynamic flow separation and diverging and converging airflow play an important role in the process of dust deposition on stone‐covered surfaces. The more pebbles protrude above the soil, the more they act as an obstacle and the more they disturb the air and dust flow creating scouring zones, flow separation bubbles and shelter areas for the dust. All these effects diminish as pebbles become more embedded in the soil. However, perturbations in dust patterns remain visible until pebbles have disappeared entirely. Copyright © 2005 John Wiley & Sons, Ltd.

The emissions and environmental impact of PM 10 and trace elements from a modern coal-fired power plant equipped with ESP and wet FGD

This study focused on the local environmental impact of a coal-fired power station with a net capacity of 600 MW e. The atmospheric emissions of numerous possible fuel gas components were calculated using the KEMA TRACE MODEL®. The STACKS model was used to calculate annual average immission levels or ground-level concentrations. Also calculated were the levels of wet and dry deposition of plume components in the vicinity of a power station. The calculated immission and deposition levels were then compared with the prevailing background concentrations and deposition levels in the Netherlands. It appears that the concentrations of air pollutants prevailing in the Netherlands are low, and that—with the exception of fine dust and NO 2/NO x —the levels do not exceed or even approach any air quality standards or limits. The present fine dust concentrations are close to the air quality standard, while the standards for NO 2/NO x sometimes are exceeded, mainly as a result of increased traffic emissions. For NO 2, the contribution of power plant emission to background concentrations is less than 2%. The increase in background fine dust concentrations attributable to fly dust ground level concentrations (immissions) is no more than 0.03%. Where the elements present in fly dust are concerned, the increase in the elemental background concentrations is smaller than 1%. The contribution to atmospheric fine dust concentrations in the vicinity of a power station attributable to the formation of secondary aerosols is negligible. The reason is that a distance of approximately 100 km, only about 3% of the gaseous sulphur dioxide and nitrogen oxides present in the plume are converted into secondary aerosols. Total wet and dry fly dust deposition over a 40×40-km area around the power station averages 1.7 mg/m 2/year, with a maximum of 25 mg/m 2/year. Depositions of this will not cause any nuisance. Trace element deposition levels are very low. The increases in background depositions are negligible, varying between 2.5% and 0.01%, depending on the element concerned. The background level of deposition of potentially acidifying substances in the Netherlands has fallen by more than 50% in the last 20 years to a value of about 3100 mol/ha/year in 2000. The main contributors to potential acid deposition are foreign sources (43%) and the agricultural industry (41%). The hypothetical power station was calculated to contribute on average only 15 acid equivalents/year across the area referred to above. This represents barely any increase in the background level of deposition (0.5%).

Northeast Asian dust storms: Real‐time numerical prediction and validation

This study is concerned with the quantitative prediction of dust storms in real time. An integrated wind erosion modeling system is used for 24‐, 48‐, and 72‐hour forecasts of northeast Asian dust events for March and April 2002. The predictions are validated with synoptic records from the meteorological network and dust concentration measurements at 12 stations in China, Japan, and Korea. The predicted spatial patterns and temporal evolutions of dust events and the predicted near‐surface dust concentrations are found to agree well with the observations. The validation confirms the capacity of the modeling system in quantitative forecasting of dust events in real time. On the basis of the predictions, dust activities in northeast Asia are examined using quantities such as dust emission, deposition, and load. During an individual dust episode, dust sources and intensities vary in space and time, but on average the Gobi Desert, the Hexi (Yellow River West) Corridor, the Chaidam Basin, the Tulufan Basin, and the fringes of the Talimu and Zhunge'er Basins are identified to be the main source regions. The Gobi Desert is the strongest dust source, where the maximum dust emission reaches 5000 μg m−2 s−1 and the net dust emission reaches 16 t km−2 d−1 in March and April 2002. Net dust deposition covers a large area, with the Loess Plateau receiving about 1.6 to 4.3 t km−2 d−1. A zone of high dust load exists along the northern boundary of the Tibet Plateau, with a maximum of around 2 t km−2 situated over the Gobi Desert. The total dust emission, total dust deposition, and total dust load for the domain of the simulation are estimated. The average (maximum) total dust emission is 11.5 × 106 (65.7 × 106) t d−1, the average (maximum) total dust deposition is 10.8 × 106 (51.4 × 106) t d−1, and the average (maximum) total dust load is 5.5 × 106 (15.9 × 106) t.

Seasonal variability of modern dust over the Loess Plateau of China

Atmospheric dust samples were collected at monthly or seasonal time intervals at six sites on the Chinese Loess Plateau during 1995–1996 and 2000. The dusts are mainly composed of mineral grains in addition to a considerable amount of organic material, especially in the case of the dusts deposited in summer. The magnetic susceptibility of these modern dusts is generally higher than that of glacial loess, and in addition they show clear seasonal variations with maximum values in the summer dust and minimum values in the winter dust. Assuming that pollution effects on modern dust can be excluded, this implies that the high susceptibility values of Quaternary paleosols may arise either from the direct effect of climate on the baseline susceptibility of the raw dust or from further enhancement by post‐depositional pedogenesis. The pattern of seasonal dust flux shows that most of the total annual dust deposition is generated by continuous deposition throughout the year rather than by dust storms in specific seasons; however, the flux does exhibit seasonal variability with highest flux occurring in spring or early summer, especially in the northern Loess Plateau. The grain‐size distribution of modern dust shows a positive‐skewed asymmetrical pattern that is analogous to Quaternary loess. Seasonal variations in dust grain size are characterized by coarsening in spring and summer and by fining in autumn and winter. At a specific site the dust grain‐size strongly depends on height above the local ground surface and decreases nonlinearly with increasing height. On the basis of vertical profiles, spatial trends and the seasonal variability of dust flux and grain size, we infer that modern dust, and thus Quaternary loess, is mostly transported at a low level of the atmosphere throughout the year with intensified dust deposition in spring and early summer.

Effect of rock fragment eccentricity on eolian deposition of atmospheric dust

The effect of rock fragment eccentricity on the deposition of airborne dust was examined in a wind tunnel. Eccentricity was defined as the ratioa/b, wherea is the longest andb the intermediate axis of the rock fragments. The effect of eccentricity on the deposition of dust on the pebbles, on the deposition of dust between and underneath the pebbles, and on total dust deposition (pebbles + interpebble space) was measured separately, and this for different values of pebble size, pebble flattening, cover density and wind speed. The more pebbles are elongated, the larger dust deposition on them will be. This effect is more pronounced as pebbles become larger, as they become less flattened, and as wind speed increases, but no correlation is observed with cover density. It also holds that the more pebbles are elongated, the less dust settles between and underneath them. This effect is more pronounced as pebbles become smaller and cover density becomes larger, but there is no relationship with pebble flattening. Whether or not there is a relationship with wind speed is unclear. Pebble eccentricity indirectly influences total dust deposition on a pebble field, since it determines whether or not (and to what extent) total dust deposition will be a function of pebble size. For circular pebbles, total dust deposition is independent of pebble size, but once pebbles become elongated, total dust deposition will be smaller on pebble fields composed of small pebbles than on pebble fields composed of large pebbles. It was also demonstrated that the more pebbles are elongated, the more the dust will tend to settle on the pebbles rather than between or underneath them. Air flow separation plays a primary role in the deposition of dust on a rock fragment field, since it determines the location and size of the low-sedimentation areas that are connected to the air flow separation bubbles. Highly-elongated pebbles oriented parallel to the wind catch much more dust (also per unit surface) than circular pebbles, the surface of which is largely located in a zone of very low deposition. Dust deposition density on highly-elongated pebbles normal to the wind, on the contrary, is equal to dust deposition on circular pebbles. It should be noted that all data in this study refer to initial dust deposition (not accumulation), since only wind velocities below the dust deflation threshold were tested.

Effect of rock fragments on eolian deposition of atmospheric dust

The effect of rock fragments and rock fragment cover on the deposition of airborne dust was examined in a wind tunnel. Four parameters were studied: pebble size, pebble flattening, cover density and wind speed. The effect of these parameters on the deposition of dust on the pebbles, on the deposition of dust bewween and underneath the pebbles, and on total dust deposition (pebbles + interpebble space) was measured separately. Deposition on the pebbles increased with pebble size, pebble flattening and wind speed. Deposition between and underneath the pebbles increased with increasing wind speed and with decreasing pebble flattening, but there was no consistent relationship with pebble size. Total dust deposition was not influenced by pebble size, pebble flattening and cover density, but it increased linearly with wind speed. It was also demonstrated that the larger and the flatter the pebbles, and the higher cover density, the more the dust will tend to settle on the pebbles rather than between or underneath them. Air flow separation seems to play a primary role in the spatial distribution of dust deposition within a rock fragment field, as it determines the location and size of the low-sedimentation areas that are connected to the air flow separation bubbles. It should be noted that all data in this study refer to dust deposition (not accumulation), since only wind velocities below the dust deflation threshold were used.

Studies on air pollution from construction plants in Helwan industrial area—I. Total dust deposition over the area

A study was carried out during the period, June 1976–May 1978 on the amount and composition of dust deposits in Helwan Industrial Area, about 24 km south-east of Cairo, Egypt. Importance was given for the construction-cement industry as a major source responsible for polluting the atmosphere of this region. 24 dust-fall collectors were set up at different sites covering the various activities in the studied area. Monthly collected deposits were estimated for their total weights, and were chemically analysed for watersoluble and insoluble components.