Concentration gradient, plumes

Airborne contaminant movement in the building depends upon the type of heat and contaminant sources, which can be classified as (1) buoyant (e.g., heat) sources, (2) nonbuoyant (diffusion) sources, and (d) dynamic sources.- With the first type of sources, contaminants move in the space primarily due to the heat energy as buoyant plumes over the heated surfaces. The second type of sources is characterized by cimtaminant diffusion in the room in all directions due to the concentration gradient in all directions (e.g., in the case of emission from painted surfaces). The emission rare in this case is significantly affected by the intensity of the ambient air turbulence and air velocity, dhe third type of sources is characterized by contaminant movement in the space with an air jet (e.g., linear jet over the tank with a push-pull ventilation), or particle flow (e.g., from a grinding wheel). In some cases, the above factors influencing contaminant distribution in the room are combined. 

A third important characteristic of a female moth s sex-pheromone plume is its nonuniformity. Simulation of odor plumes using ionized air has shown clearly that a plume is not a simple concentration gradient but instead is distinctly filamentous and discontinuous (47,48). Furthermore,... 

Calculating changes in contaminant concentration gradient between center and leading edge of plume over time... 

With a single release event, the concentration of contaminants at the plume center, and the concentration gradient (i.e., change in concentration per unit distance) between the center of the plume and its leading edge, decrease over time. 

Changes in concentration gradient between the center of the plume and its leading edge over time can be expressed as ... 

Use of pulsed air injection rather than continuous air injection may improve performance at many sites. After a system has been operating for a period of time, the concentration of contaminant in the recovered air declines. Continued injection of the same volume of injected air recovers less VOC. Injection of air in a pulsed pattern allows time for reestablishment of a greater concentration gradient toward air channels and a more uniform concentration throughout the contaminant plume area. When the system is resumed, volatilization is again the predominant removal mechanism. 

The parameter D is usually called a turbulent (or eddy) diffusion coefficient when it arises from fluid turbulence its value varies enormously from one situation to another, depending on the intensity of turbulence and on whether the environmental medium is air or water. The diagram in Fig. 1-6 shows the Fickian mass flux arising from a concentration gradient in a smoke plume. 

In both waves and unidirectional currents, the spatial distribution of odor filaments and odor-free water in a turbulent plume changes with distance from the source of the chemical signal (details reviewed in Koehl 2006 see also Weissburg, Chap. 4). For example, in a plume near the odor source the concentration gradients at the edges of odor filaments are steeper, the concentrations are generally higher,... 

The release location influences the vertical distribution of the time-averaged concentration and fluctuations. For a bed-level release, vertical profiles of the time-averaged concentration are self-similar and agreed well with gradient diffusion theory [26], In contrast, the vertical profiles for an elevated release have a peak value above the bed and are not self-similar because the distance from the source to the bed introduces a finite length scale [3, 25, 37], Additionally, it is clear that the size and relative velocity of the chemical release affects both the mean and fluctuating concentration [4], The orientation of the release also appears to influence the plume structure. The shape of the profiles of the standard deviation of the concentration fluctuations is different in the study of Crimaldi et al. [29] compared with those of Fackrell and Robins [25] and Bara et al. [26], Crimaldi et al. [29] attributed the difference to the release orientation, which was vertically upward from a flush-mounted orifice at the bed in their study. 

Answer 16.4 The leachate monitored by the piezometers located in the pit revealed that a threat to local groundwater exists. (What are the concentrations of the various ions ) A plume of leachate entering the local groundwater is observed in the direction of the water level gradient. Contamination is noticeable at a distance of how far (use the scale of the maps) The mentioned observation that metals found in the leachate do not show up in the monitoring wells is explainable by adsorption on clay material in the soil. However, this means that a hallow of metals is formed in the soil and it may reach local groundwater in the future. Therefore, metals observed in the leachate should be measured periodically in the monitoring wells. 

These microbially mediated redox processes utilize electron acceptors and produce reduced species. This will generate more reduced environments as long as there are electron donors available. The microbial population thus strongly affects their environment in the core of the plume. At the boundaries of the plume, complex microbial communities may exist, and steep redox gradients are created when dissolved electron acceptors are consumed. In addition, reoxidation of sulfides or ferrospecies by oxygen diffusing into the plume may increase the concentration of sulfate and ferric iron, which can stimulate sulfate and iron reduction in these zones as observed at Norman Landhll (Cozzarelli et al., 2000). 

---