954
sources, and were equal to 222, 248, 266, 308, 337, 400 and 532 nm. The other wavelengths used
in some experiments will be mentioned in each case in the text.
2 - EMISSION AND EXCITATION FLUORESCENCE SPECTRA OF OIL
POLLUTIONS
2.1 Fluorescence spectra of thin oil films
The oil films were made by quartz cells with known distance between parallel plates.
Fluorescence emission spectra for different oil types can be devided in two groups (see Fig. 1).
For light oils - gasoline and Diesel fuel (Fig. la) maximum of fluorescence is located in UV
spectral range, 290 and 360 nm consiquently, and does not depend on film thickness and
excitation wavelength.
For crude oils (Fig. lb,lc,ld) the spectrum maximum is located in visible region. It is
independent of excitation wavelength, but changes with film thickness alteration. With increase of
thickness the maximum wavelength shifts for 10...40 nm to longer wavelengths, the shift value
varies for different oils. This spectral behaviour of crude oil fluorescence can be explained in terms
of fluorescence reabsorption. The application of this spectral characteristics for oil identification is
impossible, since the changes in fluorescence maximum wavelength with film thickness alteration
exceed variations of this value for different crude oils.
Fluorescence excitation spectra as well as absorption spectra for all oil films, except gasoline
film, do not exhibit any structure, and their intensities decrease to longer wavelengths. The film
thickness alteration does not lead to remarkable spectral shape changes for excitation spectra.
2-2 Fluorescence spectra of oil pollutions dispersed in water
Water samples of oil pollutions were made from different oils mixed with distilled water. The
oil dispersed in water body consists of dissolved part and emulsified part of oil. We do not distinct
these two fractions in our spectroscopic investigation. When some experiments were made just
after water sample preparation, it will be specially mentioned in the text. Other samples were
studied two months later after mixing.
Fluorescence emission spectra for different oil pollutions in water are shown in Fig.2.
Fluorescence spectra of oils in water represent more complicated spectral structure and
fluorescence behaviour with excitation wavelength alteration than these for oil films As it was
mentioned above, the fluorescence maximum for oil films is independent of excitation wavelength.
On the contrary, the spectral shape and maximum locatbn for oil dispersed in water strongly
corresponded with variations of^ex. For example, fluorescence spectrum of gasoline film has only'
one band with maximum at 290 nm. This for gasoline in water has two ma xima at 290and 330 nm
(see Fig. la, 2a). The crude oil films have only onejmaximum in fluorescence spectrum located at
420...460 nm, it depends on film thickness and oil type. The same samples in water have three
components: at 290 nm, 330...340 nm, and 400...450 nm
The spectral band with maximum at 340 nm appears for all investigated aqueous samples of
OP. So we can suppose that this band is caused by water soluble oil fractions. The intensity of
fluorescence band at 340 nm gives an information about presence and content of oil dissolved in
water.
Another spectral band with maximum at 290 nm also appears for all oil pollutions in water
using shortwave excitation. This band corresponds with spectral maximum for fight oil cut (for
instance, gasoline, see Fig. la).
The spectral band in visible region can be apparently observed only for heavy oils with ^ex >
337 nm. The intensity ratio of these three bands characterize oil type (fight/medium/heavy) and
could be used for OP classification.
