Aerosol soil dust

K" Sea salt Biogenic aerosols Soil dust Biomass burning Fertilizer... 

Atmospheric transport of atrazine-contaminated aerosol particulates, dusts, and soils may contribute significantly to atrazine burdens of terrestrial and aquatic ecosystems. The annual atmospheric input of atrazine in rainfall to the Rhode River, Maryland, as one example, was estimated at 1016 mg/surface ha in 1977, and 97 mg/ha in 1978 (Wu 1981). A similar situation exists with fog water. When fog forms, exposed plant surfaces become saturated with liquid for the duration of the fog (Glotfelty et al. 1987). 

Iron was chosen as the reference element because its major source is likely to be soil and it is measured with good accuracy and precision by FIXE. Crustal abundances were taken from Mason (21). Enrichment factors greater than 1 indicate an enrichment of that element relative to crustal abundances values less than 1 indicate a depletion. The results of this calculation are shown in Table 4. For this calculation it was assumed that ammonium and nitrate accounted for all aerosol nitrogen. It is seen that Si and Ca are near their crustal abundance, indicating a probable soil dust source. The low EF for Al is probably due to a systematic error in the Al measurement rather than a true depletion. Potassium, although present in small concentrations, is slightly enriched relative to crust. The other fine aerosol species, C, N, S, and Pb are enriched by factors of thousands over their natural crustal abundance, indicating that they are not due to wind-blown dust. 

Table I. Mean abundances of crustal elements in aerosols, soil, and road dust in a rural area near Champaign, IL.

Table 1 lists a number of studies carried out in urban sites of the Eastern Mediterranean Basin that have used multivariate statistical methods to quantify the mass contribution of sources of particulate matter. In most of these studies, four or five major source categories have been detected. These categories include road/soil dust, traffic emissions, marine aerosol, fuel oil combustion emissions, biomass... 

Site/PM fraction, study soil dust Traffic Fuel oil burning aerosol unidentified... 

Carbonaceous materials (predominantly found in the fine size mode) and sometimes the dominant fraction of the total fine particle mass (Andrews et al., 2000 Putaud et al., 2004) have been usually classified as organic carbon (OC), elemental carbon (EC), and inorganic carbon (IC). The latter fraction typically consists of mineral carbonates derived almost exclusively from soil dust (Seinfeld and Pankow, 2003). Since mineral carbonates are commonly discarded from chemical aerosol mass closures, data on total carbon (TC) content of air particulate matter at sites representing different pollution levels refers only to the sum of OC and EC... 

MiUer, R. L., Tegen, I., and Perlwitz, J. (2004). Surface radiative forcing by soil dust aerosols and the hydrological cycle. J. Geophys. Res. 109, doi 10.1029/2003JD004085. 

Prospero J. M., Ginoux P., Torres O., Nicholson S. E., and Gill T. E. (2002) Environmental characterization of global sources of atmospheric soil dust identified with the Nimbus 7 total ozone mapping spectrometer (TOMS) absorbing aerosol product. Rev. Geophys. 40, article no. 1002. 

Soil dust (mineral aerosol) 1000 3000 1500 Mainly coarse ... 

Miller RL, Tegen I (1998) Climate response to soil dust aerosols. J Climate 11 3247-3267 Mirabel P, Ponche JL (1991) Studies of gas-phase clustering of water on sulfuric-acid molecules. Chem Phys Lett 183 21-24... 

Indirect effects of aerosols on climate arise from the fact that the particles act as nuclei on which cloud droplets form. In regions distant from land, the number density of SOj particles is an important determinant of the extent and type of clouds. By contrast, over land there are generally plenty of particles for cloud formation from wind-blown soil dust and other sources. Since clouds reflect solar radiation back to space, the potential link to climate is clear. The effect is likely to be most sensitive over the oceans far from land and for snow-covered regions like Antarctica, where land sources of particles have least effect. In such areas a major source of aerosols is the DMS route to SO - particles (Fig. 7.23). Thus, marine phytoplankton are not only the major source of atmospheric acidity but also the main source of cloud condensation nuclei (CCN) and so play an important role in determining cloudiness and hence climate. 

The coarse mode is largely composed of primary particles generated by mechanical pro-ce.sses such as soil dust raised by llie wind and/or vehicular traffic and construction activities. Coarse particles arc also emitted in gu.ses from industrial sources such as coal combustion and smelting. The coarse mode often peaks at about lO/tin. The chemical composition of the coarse mode is for the most part the sum of the chemical components of the primary aerosol emissions. However, there may be some contributions from gas-to-particle conversion, such as ammonium nitrate, as discussed below. 

There have been many measurements of the elemental composition of urban aerosols stimulated by the need for large databases in aerosol source apportionment (discussed in a later section). Table 13.2 compares concentrations in the fine and coarse fractions for various U.S. cities. The results show remarkable similarities in the order of magnitude of the concentrations from city to city for each element. Soil dust is a major component of the coarse fraction as indicated by the strong enrichment in aluminum and silicon in every city. The coarse fraction is much less active chemically both with respect to its mechanisms of formation and as a site for reaction, compared to the fine fraction discussed next. 

Abiotic toxic damage and accumulation of metals and nonmetals in wild and cultivated plants may result from natural geochemical loads in the soil (Kovalskij 1977) caused by macro, trace and ultratrace elements in water used for irrigation, in natural volcanoes and anthropogenic industrial pollution of the atmosphere. Water, aerosols, and dust contain a variety of aluminum, arsenic, cad-... 

The sources and chemical compositions of the fine and coarse urban particles are different. Coarse particles are generated by mechanical processes and consist of soil dust, seasalt, fly ash, tire wear particles, and so on. Aitken and accumulation mode particles contain primary particles from combustion sources and secondary aerosol material (sulfate, nitrate, ammonium, secondary organics) formed by chemical reactions resulting in gas-to-particle conversion (see Chapters 10 and 14). 

Sea spray, volcanic eruptions, soil dust, as well as some industries (cement manufacturing) produce the so called primary aerosols, i.e. the material is emitted directly in particulate state (Klockow, 1982), and they are both line and coarse. Secondary aerosols are produced in the atmosphere usually by eondensation after emission from high temperature sources, and they are fine as a rule. Considering the difference in the chemical composition it is recognized that the major components of the fine aerosols are toxie substances of anthropogenic origin such as As, Cd, Pb, Se, Zn etc. while the course aerosols are enriched in elements like Ca, Fe, Si coming from erosion, sea aerosols and other natural sources. 

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