Resuspension processes

Abstract Gaseous and particulate emissions from vehicles represent a major source of atmospheric pollution in cities. Recent research shows evidence of, along with the primary emissions from motor exhaust, important contributions from secondary (due to traffic-related organic/inorganic gaseous precursors) and primary particles due to wear and resuspension processes. Besides new and more effective (for NO emissions) technologies, non-technological measures from local authorities are needed to improve urban air quality in Europe. 

Gehrig R, Hill M, Buchmann B, Imhof D, Weingartner E, Baltensperger U (2004) Separate determination of PM10 emission factors of road traffic for tailpipe emissions and emissions from abrasion and resuspension processes. Int J Environ Pollut 22(3) 312-325... 

Several factors may account for large resuspension rates. The retrieval and deployment of the trap at the sediment surface may resuspend some particulate matter. Natural resuspension may result from storms and sediment-focusing mechanisms. Postdepositional remobilization may increase the sedimentation rate of210 Pb at the deepest point of Lake Sempach (41). Because we cannot discriminate among different resuspension processes, we assumed that the Mn concentration in the resuspended material is equal to that in the sedimenting particles at a depth of 86 m. Particulate MnO, is rapidly reduced at the sediment surface therefore, this procedure tends to overestimate the resuspension term. 

Particulate organic carbon is certainly being resuspended into the water column by the processes discussed above. These resuspension processes sometimes make a distinct delineation of the interface between the seawater and the sediment difficult. Lee et al. (1979) report measurements of sterols made on a surface floe material from the top of cores from the western North Atlantic. The sterol composition of this material, as well as the fatty acid and hydrocarbon content (J.W. Farrington, unpublished data) show that this floe material is of different composition than the underlying material. Whether this material is recently deposited and about to become part of the permanent deposit or whether it is material which is continually resuspended and moved along laterally to areas more conducive to permanent deposition is unknown. The measurement of specific organic compounds in this floe material and in samples from deep sediment traps or deep in situ pump filters should provide more insight into the question of net transport by resuspension in the deep sea. 

Based on this analysis, the major sources of trace metals in PM2.5 at the urban sites included in this study are, natural dust resuspension processes (indicated by th presence of mineral elements such as Fe and Mn), industrial emissions (Cu, As, Cd, Pb, Mo and Sn), fossil fuel refining and/or burning processes (Ni, V, Se) and traffic related emissions (Ba, Sr Sb, Zn). The mineral component comprises 55-65% of the trace metal concentrations in PM2.5 in urban areas and above 70% at rural sites. The contribution of the anthropogenic sources depends on the human... 

In Newnans Lake the wave period is only on the order of 1 s. Referring to Fig. 27.11, the consolidating bed participates in the resuspension process only along the shallow (< 1 m depth) littoral periphery of the lake. In the central portion (> Im) the sediment remains in suspension without participation by the bed. 

Thus, the resuspension rate A is the fraction removed per second by resuspension process. The use of this quantity with a suitable dispersion and deposition model would enable the movement of a radioactive nuclide from place to place to be predicted. Such an approach is necessary for estimating the radionuclide concentration in air due to resuspension downwind of an area heavily affected by the deposition process. Whether kr or A is used, it is clear that the value of the parameter must be expected to vary with many environmental variables. The most important of these environmental variables will be time after deposition, surface structure, nature of the radioactivity, wind speed, surface moisture and rate of mechanical disturbance of the surface. 

CFaT riverine models were presented for both the water column and bed sediment. They were then simplified to focus onto the non-flow resuspension soluble fraction using the quasi-steady state assumption to isolate the key water-side and sediment-side process elements. Field evidence of soluble release based on CFaT model derived data was reviewed for three rivers. Both the traditional particle background resuspension process and more recent soluble fraction process algorithms data interpretation were covered. Numerical field calibrated resuspension velocities and soluble mass-transfer coefficients were presented. Candidate water-side and sediment-side transport processes, selected from the literature were reviewed. Those that provided the best theoretical explanation and contained laboratory and/or field data support were selected. Finally, the flux and the overall transport coefficient which captures the essential features of the framework were presented. Following this the theoretical mass-transfer coefficients were applied to a site on the Fox River below De Pere Dam. Numerical calculations were made for the transport coefficients for both individual and combined processes. 

Resuspension of bottom sediments into the water column of aquatic systems represents an important source of particles and particle-associated contaminants into the water column. Unlike deposition, the resuspension process is very sporadic and short-lived, but when it does occur, the flux is generally quite large. Sediment resuspension occurs when hydraulic shear stress at the sediment-water interface rises above a critical level, sufficient to dislodge particles. Shear stress (x, dyn/cm ) is calculated as a function of shear velocity ( , cm/s) and water density (p, g/cm ) ... 

FIGURE 10.1 Illustration of the impact of deposition and resuspension processes on water column and sediment bed chemical concentrations. 

This section includes a presentation of the theory and mathematical formulation for the quantification of settling, deposition, and resuspension processes for cohesive and noncohesive sediment types. It also includes a discussion of rate governing coefficients/parameters that must be specified for each of these processes. The section concludes with a discussion of net sedimentation and tools available to evaluate the evolution of the sediment bed in depositional environments. 

Of all the processes that affect the exposure of aquatic systems to contaminated sediments, the deposition and resuspension processes reviewed in this chapter are probably most important in assessing the long-term fate of contaminants in the surface sediments of a system. As a result, these processes are important in the determination of a remediation plan for a contaminated site, because of the need to understand the stability of bottom sediments and the associated stability of contaminants in those sediments. A quantitative understanding of sediment deposition and resuspension processes is needed to address such management questions as What are the expected rate and extent of risk reduction at a site under natural recovery (no additional actions), with additional source controls, and/or with in situ remedial actions (i.e., dredging and/or capping) and Are risk reductions permanent in response to extreme events (i.e., floods, wind storms, low water level conditions) ... 

The models described in Section 10.3 are whole system models that include all processes involved in the transport and fate of contaminants in aquatic systems. Application of these models therefore demonstrates how particle deposition and resuspension affect the transport and fate of contaminants associated with those particles. The case study presented in Section 10.4 for the Lower Fox River is an example of how research knowledge and appropriate field data collection on sediment deposition and resuspension processes (reviewed in Section 10.2) have been incorporated into conceptual and numeric models (reviewed in Section 10.3) that support assessment and remediation of contaminated sediment sites. 

The dust resuspension process is one of two very significant processes that mobilize chemicals from soil surfaces to the atmospheric boundary layer. The other is termed chemical vaporization or volatilization. In the case of creating and using multimedia chemodynamic models, the flux expression must be either an advective or diffusive type relationship, containing a chemical fugacity or concentration as the state variable see Chapters 3 and 4. With the availability of Fp, it is possible to obtain the dust resuspension MTC as follows. It is defined as the ratio of the particle flux to the soil particle density or grain density Op (kg m ) ... 

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