Top PDF Ice nucleation by surrogates for atmospheric mineral dust and mineral dust/sulfate particles at cirrus temperatures

Ice nucleation by surrogates for atmospheric mineral dust and mineral dust/sulfate particles at cirrus temperatures

Ice nucleation by surrogates for atmospheric mineral dust and mineral dust/sulfate particles at cirrus temperatures

temperature range than those reported by Hung et al. (2003). Uncertainties in nucleation rate due to uncertainties in ag- glomerate particle surface area and CFDC residence times do not explain this difference. It is possible that the Hung et al. (2003) data may not reflect as large a variation in par- ticle size nucleating ice as assumed from the mode size of the input particle distributions. For example, the small frac- tions nucleated from the polydisperse populations (0.000003 to 0.003%) may represent primarily the largest particles in the distributions. It is also possible that the particles used in the respective studies were not of entirely similar mor- phology. For example, it is possible that our agglomerated particles may provide additional active sites for freezing in concave dimensions which are not present for the approxi- mately spherical particles used Hung et al. (2003). Finally, the different solutes (sulfuric acid in this study versus ammo- nium sulfate in Hung et al. (2003)) and coating amounts (rel- atively small weight fractions in this study versus relatively large weight fractions in Hung et al. (2003)) used may have had different impacts. This is not expected based on what is understood about solute impacts on freezing and the fact that even the low weight percent coatings of acid in this study would induce a typical 1.3 diameter particle growth factor by water uptake at the point of ice nucleation. Nevertheless, this discussion is not intended to distract from the fact that the general agreement between the two studies is quite good and the results in the current study extend the nucleation rate ob- servations over a wider range of J hetf for potential use in nu-
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Efficiency of immersion mode ice nucleation on surrogates of mineral dust

Efficiency of immersion mode ice nucleation on surrogates of mineral dust

nominal cooling rate due to latent heat release during freezing are taken into account. In addition, the strong dependence of heterogeneous freezing temperatures on the ATD concentration in the suspension can only be modeled by using a distribution of contact angles instead of one constant value, indicating that not all ATD particles are equal IN and reinforcing the singular hypothesis. The measured DSC curves are in

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Ice nucleation properties of mineral dust particles: determination of onset RH<sub><i>i</i></sub>, IN active fraction, nucleation time-lag, and the effect of active sites on contact angles

Ice nucleation properties of mineral dust particles: determination of onset RH<sub><i>i</i></sub>, IN active fraction, nucleation time-lag, and the effect of active sites on contact angles

of the supercooled water droplets and aqueous aerosol parti- cles, with the nucleation rate increasing for colder tempera- tures (Jeffrey and Austin, 1997; Pruppacher and Klett, 1997; henceforth P&K97). At temperatures warmer than −38 ◦ C ice formation take place heterogeneously. Heterogeneous ice nucleation requires special atmospheric aerosols called ice-forming nuclei (IN) which lower the free energy barrier for the nucleation and, depending upon different IN surface characteristics (e.g. size and morphology, solubility, epitaxial and active site distribution), determine the ice nucleation ef- ficiency. Four different heterogeneous ice nucleation mecha- nisms are hypothesized: deposition nucleation (direct depo- sition of water vapor onto the surface of the IN), condensa- tion freezing (freezing of the condensate formed on the sur- face of the IN), immersion freezing (freezing initiated by the IN located within the droplet), and contact freezing (freezing occurs the moment IN comes in contact with a supercooled water droplet or aerosol solution droplets). Recently Koop et al. (2000), and Jeffrey and Austin (1997) and references therein showed good agreement between homogeneous ice nucleation observations and theories. While observational and theoretical results for homogeneous nucleation can be compared with good agreement, theoretical treatments of heterogeneous nucleation that involve IN surfaces are very difficult to relate to observations (Cantrell and Heymsfield, 2005).
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Irreversible loss of ice nucleation active sites in mineral dust particles caused by sulphuric acid condensation

Irreversible loss of ice nucleation active sites in mineral dust particles caused by sulphuric acid condensation

sation cannot be explained by solute effects. The different re- sults obtained in this and the previously cited studies could be explained by differences in the particle generation and coat- ing methods used. Further experiments are required to bet- ter understand how the concentration of and mechanism by which sulphuric acid and other secondary material becomes mixed with dust particles affects their ice nucleation proper- ties. Since individual atmospheric mineral dust particles are frequently observed to be mixed with such soluble aerosol components (Buseck and Posfai, 1999; Russell et al., 2002; Shi et al., 2008; Sullivan et al., 2007; Sullivan and Prather, 2007), the ice nucleation properties of these mixed particles may represent the best description of a large number frac- tion of atmospheric aerosol mixing states that can potentially nucleate cirrus or mixed-phase clouds. While sulphuric acid coated mineral dust particles were observed here to be worse IN compared to untreated dust, these mixed particles are still better IN than sulphuric acid solution droplets, which can only nucleate ice homogeneously at temperatures ≤ −38 ◦ C
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An integrated modeling study on the effects of mineral dust and sea salt particles on clouds and precipitation

An integrated modeling study on the effects of mineral dust and sea salt particles on clouds and precipitation

et al., 2007; Zhang et al., 2007 among others). The model is able to explicitly resolve a complete set of atmospheric pro- cesses at resolutions ranging from tens of kilometers down to a few meters. The nesting capabilities of the model allow for sufficient representation of microphysical processes at cloud scales. The microphysics scheme of RAMS includes seven condensate species (cloud droplets, rain droplets, pristine ice, snow, aggregates, graupel and hail) and vapor. The two- moment microphysics parameterization scheme treats both the mixing ratio and number concentration of each hydrom- eteor (Meyers et al., 1997). Prediction of cloud droplet num- ber concentration is originally based on air temperature, ver- tical wind component and on a constant amount of available CCN. A lookup table has been constructed offline from a de- tailed bin-parcel model and the number of activated CCN is calculated from this table. The size and chemical proper- ties of the CCN are not taken into consideration. This ap- proach has been altered in the new version of the model by adding an explicit cloud droplet nucleation parameterization scheme (Nenes and Seinfeld, 2003; Fountoukis and Nenes, 2005). This scheme (referred to as FNS), provides a com- prehensive microphysical link between aerosols and clouds. FNS computes droplet number based on the parcel frame- work, and solves for the maximum supersaturation, s max , that
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The potential influence of Asian and African mineral dust on ice, mixed-phase and liquid water clouds

The potential influence of Asian and African mineral dust on ice, mixed-phase and liquid water clouds

Deep moist convection, e.g., in large-scale weather sys- tems that involve anvil cirrus formation, is also not well re- solved by our trajectories, even though aircraft observations between 5 and 15 km have documented such transport of dust to the upper troposphere (Cziczo et al., 2004a). This convec- tion is accompanied by large supersaturations with respect to water, likely to either nucleate ice on the best dust IN and thus cause their rapid sedimentation, or likely to coat mediocre dust IN with water and soluble species, and thus convert them from deposition to immersion IN or deactivate them altogether. Finally, the efficiency of dust IN released from evaporating ice crystals at convective outflow levels may vary greatly. While laboratory evidence suggests that the efficiency of mineral dust IN subjected to repeated cy- cles of ice nucleation increases (Mason and Maybank, 1958; Roberts and Hallett, 1968; Knopf and Koop, 2006), the pres- ence of substances other than water, e.g., sulphuric acid, is found to have neutral to negative effects on the ice nucle- ation efficiency of dust IN (Archuleta et al., 2005; Knopf and Koop, 2006; Eastwood et al., 2009). Additionally, coat- ings of ammonium sulphate (an inorganic salt) are found to inhibit ice nucleation at higher temperatures while increas- ing IN efficiency at temperatures below the ammonium sul- phate efflorescence point (Eastwood et al., 2009). Moreover, the introduction of organic substances in cloud processing may further complicate the situation, as field measurements have shown that organic-rich particles preferentially remain unfrozen in homogeneous nucleation processes (Cziczo et al., 2004b), and, more recently, M¨ohler et al. (2008) have shown with laboratory experiments that secondary organic coatings markedly suppress the ice nucleation efficiency of mineral dust IN at cirrus temperatures. As our goal is to assess the availability of bare mineral dust deposition IN in cirrus-forming regions, the inability to fully resolve (deep) convection is neglected in the following, i.e. we do not fol- low up on the possibility that dust particles, after passing the “tropical convective dust pump” may be re-released as po- tentially still potent, or even pre-activated ice nuclei. Since deep convection is relatively more important than synoptic scale ascent in the tropics (as opposed to mid-latitudes), this may be a source of bias.
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Sedimentary and mineral dust sources of dissolved iron to the World Ocean

Sedimentary and mineral dust sources of dissolved iron to the World Ocean

Boyd, P. W., Watson, A. J., Law, C. S., Abraham, E. R., Trull, T., Murdoch, R., Bakker, C. E., Bowei, A. R., Buesseler, K. O., Chang, H., Charette, M., Croot, P., Downing, K., Frew, R., Gall, M., Hadfield, M., Hall, J., Harvey, M., Jameson, G., LaRoche, J., Liddicoat, M., Ling, R., Maldonado, M.T ., McKay, R. M., Nodder, S., Pickmere, S., Pridmore, Rintoul, S., Safi, K., Sutton, P., Strzepek, R., Tanneberger, K., Turner, S., Waite, A., and Zeldis, J.: A mesoscale

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A case of extreme particulate matter concentrations over Central Europe caused by dust emitted over the southern Ukraine

A case of extreme particulate matter concentrations over Central Europe caused by dust emitted over the southern Ukraine

Unvegetated areas containing fine and loose sediments can be sources of dust particle emission when strong surface winds occur. The Sahara is the most important source for soil dust worldwide; it is estimated to be responsible for 50% or more of the global atmospheric dust load (Goudie and Middleton, 2001). Ground dusts are mainly emitted via the process of saltation (Gillette, 1978; Shao et al., 1993; Marticorena and Bergametti, 1995), where sand particles that are easily lifted from the surface impact on the ground. The release of ki- netic energy breaks the binding of finer soil particles like clay, which are then available for long-range transport. In some instances direct particle lifting has also been observed (Loosmore and Hunt, 2000), but this process is usually only of local importance. Generally, strong winds are required to initiate and sustain dust emission from soils. These are often related to convective systems or the passages of cold fronts (Pye, 1987; Shao, 2000). Dust injected into high atmospheric levels of up to several kilometers can be transported over hor- izontal distances of thousands of kilometers in strong wind systems (Alpert et al., 2004).
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Wet and dry deposition of mineral dust particles in Japan: factors related to temporal variation and spatial distribution

Wet and dry deposition of mineral dust particles in Japan: factors related to temporal variation and spatial distribution

Figure 2 shows the wet deposition flux of mineral dusts at six sites during October 2008–December 2010. Time inter- vals of flux presented in Fig. 2 are depicted with the origi- nal sampling duration. Therefore, the horizontal width is nar- rower for short-term sampling on a dust event predicted by Kosa event forecasts. Wet deposition flux was high in spring (February–May) and low in summer (July–September), irre- spective of the site location and the year of observation. Tem- poral variations of wet dust deposition were not always syn- chronous among sites because of the migration of the precip- itation region from west to east and the local effects of winter monsoon (drizzle precipitation) at Tottori, Toyama, and Sap- poro. However, nearly simultaneous wet depositions at mul- tiple sites were observed five times (late-January, late Febru- ary, mid-March, mid-April, and late December) in 2009, and five times (mid-March, late March to early April, late April, late December) in 2010. These simultaneous deposi- tions were roughly divided into two regional patterns as west- ern to central parts and central to northern parts of Japan.
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Dust–air pollution dynamics over the eastern Mediterranean

Dust–air pollution dynamics over the eastern Mediterranean

The transport of Saharan dust in addition to that from Ara- bian deserts are the main sources of atmospheric dust in the EM region (Pey et al., 2013), a regular atmospheric phe- nomenon in this region (Ganor et al., 2010). Typically, the majority of dust outbreaks are related to steep surface pres- sure gradients between northern Africa and the Mediter- ranean (Dayan et al., 2008). Saharan dust is generally mo- bilized in Libya, Egypt and the Bodele Depression (Pey et al., 2013) during the local dry season from October to April (Goudie and Middleton, 2006) and then transported over the EM by Sharav cyclones (Ganor and Mamane, 1982; Moulin et al., 1998; Goudie and Middleton, 2006; Ganor et al., 2010) or Khamsin events (Ganor and Mamane, 1982). These cyclones are generated along the polar front and sub- tropical jet streams (Kallos et al., 2006) as a result of dif- ferential heating between relatively colder oceanic waters to the north and warmer land masses to the south (Goudie and Middleton, 2006). These synoptic conditions are usually as- sociated with a cold front and are often accompanied by rain over the EM (Alpert and Ganor, 1993). In addition, the EM is affected by dust transport from the Negev desert, controlled by a range of synoptic systems, e.g., Cyprus lows, Red Sea troughs, Persian troughs, anticyclones over the Levant and to the east of the region. The majority, i.e., about two-thirds of the yearly dust events are caused by Cyprus lows (Dayan et al., 2008). Since Cyprus lows are often associated with precipitation, the residence time of dust particles in the atmo- sphere can be relatively short. In case of a barometric trough penetrating from the Red Sea into the EM, it can be as short as 1 day (Dayan et al., 1991). Dayan et al. (2008) studied events where dust is transported from the Sahara, indicat- ing that the average residence time is about 4 days before the dust is removed by rain. The combination of dust trans- port from the Sahara and Arabian deserts results in numer- ous and very intense dust episodes over the EM and Cyprus (Pey et al., 2013). In general, the transport of Saharan dust usually extends into relatively deep atmospheric layers and is characterized by a regional extension over the Mediter- ranean Basin. Typically, dust is transported over the EM at an elevation of 1.5–6.5 km above sea level and commonly at about 2.5 km (Levin et al., 2005; Papayannis et al., 2005;
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Comparison of satellite microwave backscattering (ASCAT) and visible/near-infrared reflectances (PARASOL) for the estimation of aeolian aerodynamic roughness length in arid and semi-arid regions

Comparison of satellite microwave backscattering (ASCAT) and visible/near-infrared reflectances (PARASOL) for the estimation of aeolian aerodynamic roughness length in arid and semi-arid regions

of 400 m width: we attempted to use this data set as well, but the spatial resolution of our satellite data and their high sensitivity to orography made the comparison with in situ measurements meaningless in such heterogeneous and mountain environments. It has been verified that the aeolian roughness lengths reported in Table 1 are also compatible with results obtained in wind tunnels over bare surfaces (Xue and Sun,

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Composition, size distribution, optical properties, and radiative effects of laboratory-resuspended PM<sub>10</sub> from geological dust of the Rome area, by electron microscopy and radiative transfer modelling

Composition, size distribution, optical properties, and radiative effects of laboratory-resuspended PM<sub>10</sub> from geological dust of the Rome area, by electron microscopy and radiative transfer modelling

laboratory-resuspended from the bulk rocks samples, and from road dust, by a resuspension chamber, and collected by low-volume sampling on polycarbonate membranes for SEM XEDS microanalysis. It is worth noting that, among laboratory methods of dust generation or resuspension from bulk materials, fluidization by mechanical ventilation in a re- suspension chamber is widely acknowledged, either for not affecting both the complete resuspension potential of the source material and the original size distribution of the re- suspended particles in the material itself, and for simulating the resuspension of dust previously deposited at a site (Gill et al., 2006, and references therein). By this approach, good approximation of the field sampling at a dust source can be achieved, making it suitable for studies on the mineralogical and microphysical characterization of mineral dust (Gill et al., 2006, and references therein; Feng et al., 2011; Aimar et al., 2012; Dobrzhinsky et al., 2012).
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Arabian Red Sea coastal soils as potential mineral dust sources

Arabian Red Sea coastal soils as potential mineral dust sources

Abstract. Both Moderate Resolution Imaging Spectrora- diometer (MODIS) and Spinning Enhanced Visible and In- fraRed Imager (SEVIRI) satellite observations suggest that the narrow heterogeneous Red Sea coastal region is a fre- quent source of airborne dust that, because of its proximity, directly affects the Red Sea and coastal urban centers. The potential of soils to be suspended as airborne mineral dust depends largely on soil texture, moisture content and par- ticle size distributions. Airborne dust inevitably carries the mineralogical and chemical signature of a parent soil. The existing soil databases are too coarse to resolve the small but important coastal region. The purpose of this study is to better characterize the mineralogical, chemical and physical properties of soils from the Arabian Red Sea coastal plain, which in turn will help to improve assessment of dust ef- fects on the Red Sea, land environmental systems and ur- ban centers. Thirteen surface soils from the hot-spot areas of windblown mineral dust along the Red Sea coastal plain were sampled for analysis. Analytical methods included op- tical microscopy, X-ray diffraction (XRD), inductively cou- pled plasma optical emission spectrometry (ICP-OES), ion chromatography (IC), scanning electron microscopy (SEM) and laser particle size analysis (LPSA). We found that the Red Sea coastal soils contain major components of quartz and feldspar, as well as lesser but variable amounts of am- phibole, pyroxene, carbonate, clays and micas, with traces of gypsum, halite, chlorite, epidote and oxides. The range of minerals in the soil samples was ascribed to the variety of igneous and metamorphic provenance rocks of the Arabian Shield forming the escarpment to the east of the Red Sea coastal plain. The analysis revealed that the samples contain compounds of nitrogen, phosphorus and iron that are essen- tial nutrients to marine life. The analytical results from this
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The impact of atmospheric mineral aerosol deposition on the albedo of snow and sea ice: are snow and sea ice optical properties more important than mineral aerosol optical properties?

The impact of atmospheric mineral aerosol deposition on the albedo of snow and sea ice: are snow and sea ice optical properties more important than mineral aerosol optical properties?

Figure 5 shows the change in albedo at 550 nm of an increasing mass-ratio of the two most common types of mineral dust found in the Arctic for three di ff erent types of sea ice (first y[r]

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Properties of cloud condensation nuclei (CCN) in the trade wind marine boundary layer of the western North Atlantic

Properties of cloud condensation nuclei (CCN) in the trade wind marine boundary layer of the western North Atlantic

Oxford, Oxfordshire, UK). Images were acquired with a res- olution of 1.32 pixels per nm. During the electron beam anal- ysis, the particles absorbed energy and heated up. Hence, the volatile particulate material evaporated and only the refrac- tory fraction remained on the substrate. To determine the original state, one image was recorded right at the begin- ning of the electron bombardment. When no more change of the remaining particle fraction was observed, a second image was recorded. Changes to the particles were derived from image comparison. An exact temperature under this electron bombardment can not be determined. However, the temperature conditions can be considered to be similar for all measurements, as identical instrument settings were used. From a chemical analysis it becomes obvious that nitrate and sulfate evaporated, while sodium chloride, all mineral dust components and soot remained stable (Kandler et al., 2011). From the decomposition behaviour and the absence of sodium chloride melting, we concluded that the temperature is between 200 and 800 ◦ C, most likely higher than 300 ◦ C (Kiyoura and Urano, 1970; Lide, 2009). Semi-automatic im- age analysis (determination of the particle projected area and the projected-area-equivalent diameter (PAED)) was per- formed with the ImageJ software 1.47c (Rasband, 2012). As the brightness of the images was uneven, a manual thresh- olding combined with additional manual particle outlining was required instead of an automatic brightness-based seg- mentation procedure. The volume fraction of refractory ma- terial inside each particle was estimated as the ratio of the projected area after evaporation to the projected area before evaporation, raised to the power of 1.5.
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Does the size distribution of mineral dust aerosols depend on the wind speed at emission?

Does the size distribution of mineral dust aerosols depend on the wind speed at emission?

Fig. 4. Wind tunnel measurements of the speed of ∼250–300 µm saltating particles report that the mean horizontal speed at the surface stays constant with u∗ (symbols). Similarly, Namikas (2003) inferred from his field measurements that the speed with which saltating particles are launched from the surface is independent of u∗ (solid orange line). These experimental results are supported by predictions for 250 µm sand by a recent numerical model (dash-dotted blue line; Kok and Renno, 2009) and theory (Ungar and Haff, 1987; Kok, 2010a) (dotted green line denotes Eqs. (13) and (14) of Kok, 2010a). The assumption of increasing saltator speed by Alfaro and Gomes (2001; dashed red line) and Shao (2001; dashed purple line) is thus likely incorrect. (The impact speed of v imp = 20u∗ assumed by Alfaro and Gomes (see their Eq. 1) and the launch speed and angle of ∼0.70 m s −1 and ∼35 ◦ inferred by Namikas (2003)
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Comment on evidence for surface-initiated homogenous nucleation

Comment on evidence for surface-initiated homogenous nucleation

expected and as a result, surface nucleation should be favored. In fact, Cahn argues that perfect wetting should be observed at a critical point and that a phase transition from perfect to imperfect wetting should take place at some temperature below the crit- ical temperature. Cahn’s argument does not imply that perfect wetting is improbable away from the critical point. Wetting transitions have nothing to do with critical points

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A 10 year record of black carbon and dust from a Mera Peak ice core (Nepal): variability and potential impact on melting of Himalayan glaciers

A 10 year record of black carbon and dust from a Mera Peak ice core (Nepal): variability and potential impact on melting of Himalayan glaciers

impact climate, air quality and, indirectly, the evolution of the cryosphere. Quantifying emissions is one of the major chal- lenges for the development of air quality and climate poli- cies (Fowler et al., 2009; Isaksen et al., 2009) and quantifi- cation should account for different changes in human-related emissions and natural emissions over time as well as changes in their geographical distribution. Major uncertainties in past and current global inventories of anthropogenic and natural emissions limit the establishment of a reliable framework of emission inventories that is required for realistic emission scenarios. This is especially true for the Indian subconti- nent where reliable estimates of past and current emissions are crucially lacking. India is one of the two largest anthro- pogenic aerosol generating countries in the world (Lu et al., 2011). In the past decade, India has been identified as a hot spot in terms of high aerosol optical depth (AOD) observed from space (Prasad and Singh, 2007) with components such as sulfate, organic carbon (OC) or black carbon (BC) playing a very active role. India on its own contributes 10 to 20 % of all current aerosol emissions worldwide (Bond et al., 2007) and has therefore received the greatest attention from com- pilers of emission inventories.
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Delivery of anthropogenic bioavailable iron from mineral dust and combustion aerosols to the ocean

Delivery of anthropogenic bioavailable iron from mineral dust and combustion aerosols to the ocean

ported in Ito (2013), the oil combustion from shipping mainly contributes to high Fe sol- ubility at low Fe loading observed over the high latitude North Atlantic Ocean (Fig. 5a). In this study, low Fe solubility near North African continent was successfully simulated. While our model has incorporated the initial rapid Fe release rate in acid solutions with oxalate explicitly, the comparisons with observations support the suppression of

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Aerosols optical and physical characteristics and direct radiative forcing during a "Shamal" dust storm, a case study

Aerosols optical and physical characteristics and direct radiative forcing during a "Shamal" dust storm, a case study

of dust phenomena impacts the local economy by affecting aircraft aviation and road transportation (De Villiers and Van Heerden, 2007). In certain occasions of severe dust storm it brings the whole locality to a stand still. On the other hand, dust can also have beneficial effects where it deposits. For example, Central and South American rain- forests get most of their mineral nutrients from the Sahara dust fallout (Swap et al.,

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