Resuspension factor

The conditions in Nevada are favourable for resuspension of Pu from the ground. Because the area round the N.T.S. is arid, Pu has not been moved down the soil profile by leaching or by cultivation, and more than 50% of the Pu was found to be in the top 20 mm of soil about 15 a after deposition (Anspaugh et al., 1975). The mechanisms of resuspension of particles from the ground are considered in a later chapter. The resuspension factor Kr is defined ... 

The resuspension of radioactive fallout can be related to the activity originally deposited. If 4 (Bq m-2) is the activity on the ground, xi (Bq m-3) the airborne activity, and Q (Bq m-2 s-1) the vertical flux, the resuspension factor is defined. 

Anspaugh et al. (1975, 1976) studied resuspension at the GMX location on the Nevada Test Site, where plutonium was disseminated by small non-nuclear explosions about 30 years ago. To obtain representative values of the resuspension factor, ideally a large and uniform area of deposited activity is required, in order that there should be a constant flux layer in the air near the ground. The fallout of Pu at the GMX site is non-uniform, so Anspaugh et al. analysed their measurements of x in relation to a model calculation of the concentration expected from the areal source. 

Hotzl et al. (1989) measured the airborne concentration of 137Cs in Germany in the year subsequent to the Chernobyl accident. Though low compared to the concentrations immediately after the accident, the levels were higher than could be ascribed to the lingering effects of weapon tests, and were found to correlate, in different locations, with the amount of Chernobyl fallout. Comparing the airborne concentration with that of 137Cs in the top 10 mm of soil, Hotzl et al. deduced a resuspension factor Kr — (3 1) x 10-9 m-1. Concentrations were found to increase with wind speed as ul s, a result very similar to that found in Nevada (equation (6.24)). 

The resuspension factor Kr was found to depend on the amount of movement in the laboratory, with values ranging from 10-5 to 10-4 m-1 (oxide particles) and from 10-6 to 10-5 m-1 (Pu applied in solution). 

Uranium thus deposited (dry or wet) will usually reside on land or be deposited on surface waters. If land deposition occurs, the uranium can incorporate into the soil or adhere to plant surfaces, be resuspended in the atmosphere as a result of wind action, or be washed from the land into surface water and groundwater. Resuspension factors are typically quite low (10 ) and protective against significant exposures, but this may not apply to windy and arid areas. Resuspension into the air can be an inhalation source even after the plume or source has disappeared. 

This definition of the resuspension factor, kr, implies an equilibrium relationship between the two quantities which may be achieved only over an extensive area of uniform deposition. In principle, when the deposition varies spatially, resuspension would be better predicted by us ing the resuspension rate, A in s which is defined as the ratio of vertical flux (Bq m and the radioactivity deposited on the ground (Bqm ) ... 

A simple exponential function for the resuspension factor, kr, gives a reasonable description of the decrease with time (Garland and Pattenden, 1989) as follows ... 

Baskaran and Santschi (1993) examined " Th from six shallow Texas estuaries. They found dissolved residence times ranged from 0.08 to 4.9 days and the total residence time ranged from 0.9 and 7.8 days. They found the Th dissolved and total water column residence times were much shorter in the summer. This was attributed to the more energetic particle resuspension rates during the summer sampling. They also observed an inverse relation between distribution coefficients and particle concentrations, implying that kinetic factors control Th distribution. Baskaran et al. (1993) and Baskaran and Santschi (2002) showed that the residence time of colloidal and particulate " Th residence time in the coastal waters are considerably lower (1.4 days) than those in the surface waters in the shelf and open ocean (9.1 days) of the Western Arctic Ocean (Baskaran et al. 2003). Based on the mass concentrations of colloidal and particulate matter, it was concluded that only a small portion of the colloidal " Th actively participates in Arctic Th cycling (Baskaran et al. 2003). 

In developing a multiple regression model for apportioning sources of TSP in New York City, Kleinman, et al.(2) selected Pb, Mn, Cu, V and SO, as tracers for automotive sources, soil-related sources, incineration, oil-burning and secondary particulate matter, respectively. These were chosen on the basis of the results of factor analysis and a qualitative knowledge of the principal types of sources in New York City and the trace metals present in emissions from these types of sources. Secondary TSP, automotive sources and soil resuspension were found to be the principal sources of TSP in 1974 and 1975 ( ). 

When MN(C) is included as a variable the coefficient for PB became statistically insignificant (p = 0.36). The coefficient for PB in equation (15) was a factor of two smaller than in equation (16) however, this is not a significant difference in view of the uncertainties of the coefficients, particularly in equation (16). If additional variables (CU or MN ) were included in the multiple regression analysis, these were placed in the equations ahead of PB the coefficient for PB was not statistically significant in any of these equations and often negative. This can be seen in equation (16). If MN was used as a mixed auto/soil tracer, equation (17) was obtained. Although this does not allow separate estimates of the contributions of automobiles and soil resuspension, the particle-size of the tracer is more appropriate. 

The most appropriate models for CYC is probably equation (14) as this is the simplest and is most closely related to the results of the factor analysis which indicated that the variances in CYC were most closely related to those in V and PB. The inclusion of coarse particle manganese as a soil tracer diminished the significance of the coefficient of PB and the contribution of automotive sources. Ideally, MN would be used as a tracer for resuspended soil but Interferences from the use of MMT as a fuel additive during part of the period in which this data were collected make this a mixed source tracer for the contributions of automobiles and soil resuspension. 

Receptor models are widely used tools for apportioning concentrations of pollutants to different sources. They can be factor analytical methods (PMF, PCA, UNMIX, etc.) or chemical mass balance (CMB). On the one hand, these methods revealed to be very valuable to identify the main sources/categories of PM pollution (road traffic, secondary particles, fuel oil combustion, sea salt, etc.) but on the other hand they experienced difficulties in separating the contributions of collinear sources such as mineral dust (natural resuspension) and road dust (anthropogenic) or co-variant sources such as vehicle exhaust and road dust [34, 44, 45, 49, 55, 58, 110-113]). Significant improvements were made with the use of combination of models or constrained models such as the Multilinear Engine (ME-2). 

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... 

Amato F, Karanasiou A, Moreno T, Alastuey A, Orza JAG, Lumbreras J, Borge R, Boldo E, Linares C, Querol X (2012) Emission factors from road dust resuspension in a Mediterranean freeway. Atmos Environ 61 580-587... 

Early diagenesis is typically described as a steady-state phenomenon however, unless very long-term geological timescales are considered, steady-state conditions are generally not common in shallow turbid environments such as estuaries. There are many factors that contribute to these non-steady-state conditions, such as variations in sedimentation rate, inputs of organic matter, chemistry of bottom waters and sediments, bioturbation rates, and resuspension (Lasagna and Holland, 1976). Consequently, numerous attempts... 

Notes. The different brands of streptavidin magnetic beads have different molarities of attached streptavidin, different resuspension protocols, and different capture properties. Bead volumes given in this protocol are for Promega (Madison, WI) paramagnetic particles (No. Z5241) prepared as indicated below. If other beads are used, appropriate volumes may differ by a factor of 3 or more from those presented. 

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. 

Quantitative measures of emissions are emissions factors and emission rates. A source emission factor is typically defined as the amount of a chemical species, mass, particle number, etc. emitted per unit mass of fuel burned or per defined task performed [3]. The former is often referred to as a mass-based emission factor and has a unit such as grams per kilogram. The latter can be called a task-based emission factor. The unit of the task-based emission factor depends on the definition of the tasks. For example, a task can be the number of cigarettes smoked or a certain distance driven by a motor vehicle and thus the units may be grams per cigarette or grams per kilometre, respectively. The emission rate, on the other hand, is the amount of a chemical species, mass, particle number, etc. emitted by the source per unit time. For example, emissions from stoves are usually characterised in terms of emission factors. Similarly, re-entrainment of settled dust to the air is represented by resuspension rates. Emission factors and emission rates vary significantly... 

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