Both the degradation and the toxicity of dispersants depend on the chemicals chosen within the formulation. Compounds which interact too harshly with oil dispersants should be tested to ensure that they meet three criteria: From Wikipedia, the free encyclopedia. Views Read Edit View history. Retrieved 4 April
More dispersant may be required if the sea energy is low. The salinity of the water is more important for ionic-surfactant dispersants, as salt screens electrostatic interactions between molecules. The viscosity of the oil is another important factor; viscosity can retard dispersant migration to the oil-water interface and also increase the energy required to shear a drop from the slick.
Viscosities below 2, centi poise are optimal for dispersants. If the viscosity is above 10, centipoise, no dispersion is possible. There are five requirements for surfactants to successfully disperse oil: The effectiveness of a dispersant may be analyzed with the following equations. Developing well-constructed models accounting for variables such as oil type, salinity and surfactant are necessary to select the appropriate dispersant in a given situation.
Two models exist which integrate the use of dispersants: Mackay's model and Johansen's model. This causes the oil slick's behavior to be more dominated by vertical diffusion than horizontal advection.
One equation for the modeling of oil spills is: Mackay's model predicts an increasing dispersion rate, as the slick becomes thinner in one dimension. The model predicts that thin slicks will disperse faster than thick slicks for several reasons.
Thin slicks are less effective at dampening waves and other sources of turbidity. Additionally, droplets formed upon dispersion are expected to be smaller in a thin slick and thus easier to disperse in water. The model also includes: The model is lacking in several areas: Johansen's model is more complex than Mackay's model. It considers particles to be in one of three states: The empirically based model uses probabilistic variables to determine where the dispersant will move and where it will go after it breaks up oil slicks.
The drift of each particle is determined by the state of that particle; this means that a particle in the vapor state will travel much further than a particle on the surface or under the surface of the ocean. Oil dispersants are modeled by Johansen using a different set of entrainment and resurfacing parameters for treated versus untreated oil.
This allows areas of the oil slick to be modeled differently, to better understand how oil spreads along the water's surface. Surfactants are classified into four main types, each with different properties and applications: Anionic surfactants are compounds that contain an anionic polar group. Examples of anionic surfactants include sodium dodecyl sulfate and dioctyl sodium sulfosuccinate.
Many of these compounds are quaternary ammonium salts , as well as cetrimonium bromide CTAB. An example of a zwitterionic compound is phosphatidylcholine , which as a lipid is largely insoluble in water. Surfactant behavior is highly dependent on the hydrophilic-lipophilic balance HLB value.
The HLB is a coding scale from 0 to 20 for non- ionic surfactants, and takes into account the chemical structure of the surfactant molecule. A zero value corresponds to the most lipophilic and a value of 20 is the most hydrophilic for a non-ionic surfactant.
Compounds with an HLB value above 13 will form a clear solution in water. Two formulations of different dispersing agents for oil spills, Dispersit and Omni-Clean, are shown below. A key difference between the two is that Omni-Clean uses ionic surfactants and Dispersit uses entirely non-ionic surfactants. Omni-Clean was formulated for little or no toxicity toward the environment.
Dispersit, however, was designed as a competitor with Corexit. Dispersit contains non-ionic surfactants, which permit both primarily oil-soluble and primarily water-soluble surfactants. The partitioning of surfactants between the phases allows for effective dispersion. Both the degradation and the toxicity of dispersants depend on the chemicals chosen within the formulation.
Compounds which interact too harshly with oil dispersants should be tested to ensure that they meet three criteria: Dispersants can be delivered in aerosolized form by an aircraft or boat. Sufficient dispersant with droplets in the proper size are necessary; this can be achieved with an appropriate pumping rate.
Currently, the DWD consists of roughly occupants. Additionally, it runs Germany's densest network of meteorological measurement points with full-time meteorological stations 60 of them manned , as well as about extraordinal weather stations run by volunteering amateurs From Wikipedia, the free encyclopedia.
For other uses, see subarctic climate. History of numerical weather prediction and Numerical weather prediction. Brazilian Navy Hydrographic Center. Archived from the original on Consortium for Small-scale Modeling 6. Berliner Morgenpost in German. Retrieved from " https: Governmental meteorological agencies in Europe Offenbach am Main.