Chemistry Reference
In-Depth Information
to be applied that the helicopter flies sufficiently high, in order to avoid
disturbance of the water wave field by the downwash-effect of the helicop-
ter.
If no helicopter is available, fluid slick-forming substances may also be
distributed on the sea surface from aboard a boat. However, in this case the
bulk material must be poured overboard very close to the water surface, in
order to get optimum spreading conditions. Furthermore, the boat should
be moved very slowly backwards out-of the developing slick, while additi-
onal slick material is being poured continuously onto the sea surface. Dur-
ing this procedure, propeller-induced water turbulence should be avoided
as far as possible.
Several particularly strongly wave damping substances such as PME
(see Figure 2) are solid and must be solved prior to their application, be-
cause solid PME crystals will not spread on the sea surface. The choice of
an appropriate solvent is important for the spreading procedure, which de-
termines the morphology of the developing slick and thus the influence on
the water wave spectrum. The latter aspect is discussed in a separate paper
by Hühnerfuss et al. in this monograph. In many cases, ethanol is assumed
to be an excellent choice as a solvent. Its potential influence on the spread-
ing velocity of the respective surface-active compound is shown for OLA
in Figure 4. However, it has to be stressed that the application of organic
solvents requires specific safety precautions, which in each country may be
based on different safety regulations.
The distribution of crude oil mixtures on the water surface is dominated
by the viscosity of the crude oil mixture as well as on the specific environ-
mental conditions (currents, wind and water wave directions and magni-
tudes). As crude oil spills will form layers that remain orders of magnitude
thicker than those of monomolecular slicks, considerably higher amounts
of oil material are needed to generate experimental crude oil spills. Typi-
cally some cubic metres of crude oil have to be pumped onto the sea sur-
face, i.e., three to four orders of magnitude more than in the case of artifi-
cial sea slicks. Furthermore, caution should be applied with the application
of crude oils, because the transformation of the chemical constituents is
much slower than that of the components of quasi-biogenic sea slicks. Fur-
thermore, regulations of the respective countries have to be checked.
4. Damping of water waves by sea slicks or oil spills
The different water wave damping mechanisms of sea slicks and crude oil
spills can be understood on the basis of their different influences on the
structure and physicochemical characteristics of the air/water interface.
