Deposition pathways

Fig. 10-12. Atmospheric processes involved in acidic deposition, The two principal deposition pathways are dry deposition (nonrain events) and wet deposition (rain events).

Modeling Intakes. To determine the significance of diet and inhalation as sources of internally deposited U and Th, dietary and inhalation estimates for the general population were used in an Oak Ridge National Laboratory (ORNL) model, INREM II (7). A schematic of the intake and deposition pathways considered by the model are depicted in Fig. 1. Uranium in the typical diet is about... 

Methanesulfonic acid, although it comprises a relatively small fraction of total non sea-salt aerosol sulfur, has been shown (2) to be a ubiquitous component of marine aerosols. Its occurrence and distribution have been suggested as of use as an in situ tracer (3.4) for oceanic emissions and subsequent reaction and deposition pathways of organosulfur compounds and dimethyl sulfide in particular. 

This table considers the whole wet deposition pathway, no distinction between RAiNOUT and washout. 

The CO disproportionation reaction (37) has been used as the carbon deposition pathway in the majority of studies 48, 54, 56, 58-60). Carbon has also been deposited via hydrocarbon hydrogenolysis 54, 61-63) and, notably, via the FT synthesis reactions 35-37, 45). Particularly the initial studies involved nickel substrates ruthenium, cobalt, and iron were also studied. 

Cloud droplets are typically far more acidic than precipitation droplets collected at the ground. In essence cloud drops are small and have not been subjected to the dilution associated with growth to the size of raindrops, snowflakes, and so on, nor the neutralization as sociated with the capture of surface-derived NH3 and alkaline particles held in layers at lower altitudes. Interception of these droplets therefore provides a route by which concentrated solutions of sulfate and nitrate can be transferred to foliage in high-elevation areas that are exposed to clouds. Only limited areas of the eastern part of the United States are frequently exposed to such deposition, but for these sensitive areas cloud interception is an important acid deposition pathway. 

The behavior and fate of SVOCs in the atmosphere greatly depends on the distribution of compounds between different sub-compartments of the atmosphere such as atmospheric gaseous and particulate phases. It has been summarized that gas-particle partitioning is controlling the relative importance of different deposition pathways for SVOCs from the atmosphere to the terrestrial and aqueous surface (Bildleman 1988). 

Inorganic nanoshell-coated organic polystyrene beads with well-defined nanostructures are attractive because of their applications in the fields of SERS, catalysis, biochemistry, and chemical sensors. The core-shell type composite materials are in the frontier of advanced research, in which the shell component determines the surface properties and the core component indirectly induces the other properties of the system. Bimetallic nanosheUs on functionalized polystyrene beads have been fabricated through a layer-by-layer deposition pathway involving the electrostatic interaction of the polystyrene moiety. 

FIGURE 9 The various atmospheric deposition pathways of en-vironmentai chemicais. 

Dry deposition of chemical associated with atmospheric aerosols to a plant canopy is in many ways similar to the corresponding deposition pathway to water and soil as discussed in Chapter 6. Atmospheric aerosols can be deposited via Brownian diffusion (dominant for small aerosols (< 0.1 p,m) and characterized by intermediate deposition velocities, see Figure 6.4), impaction or interception (medium size aerosols (< 2 p,m), low deposition velocities), or sedimentation (large aerosols (> 2 jim), high deposition velocities). 

Organic chemicals can directly reach above ground plant tissues by vapor and particle deposition as discussed in Chapter 7, or they many reach below ground tissues by way of the roots, the emphasis of this chapter. Atmospheric deposition pathways to above ground plant components are likely to be more important for hydrophobic and less volatile compounds, while the root sorption and uptake pathway... 

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