The Area refers to the area under the absorbance/wavelength curve, which is determined using the trapezoidal rule. The absorbances are measured at 340, 370, and 400 nm. Area = 30(Abs340 + Abs370)/2 + 30(Abs340 + Abs400)/2 (1) The dispersant effectiveness may then be calculated using the equation below. Effectiveness (%) = Total oil dispersed x 100/(ρoilVoil) ρoil = density of the test oil (g/L) Voil = volume of oil added to test flask (L) Total oil dispersed = mass of oil x 120mL/30mL Mass of oil = concentration oil x VDCM VDCM = final volume of DCM-extract of water sample (0.020 L) Concentration of oil = area determined by Equation (1) / slope of calibration curve Dispersion models 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. There are several parameters which must be considered when creating a dispersion model, including oil-slick thickness, advection, resurfacing and wave action. A general problem in modeling dispersants is that they change several of these parameters; surfactants lower the thickness of the film, increase the amount of diffusion into the water column and increase the amount of breakup caused by wave action. 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: where h is the oil-slick thickness is the velocity of ocean currents in the mixing layer of the water column (where oil and water mix together) is the wind-driven shear stress f is the oil-water friction coefficient E is the relative difference in densities between the oil and water R is the rate of spill propagation 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: An expression for the diameter of the oil drop Temperature dependence of oil movement An expression for the resurfacing of oil Calibrations based on data from experimental spills The model is lacking in several