958
The spectral rules obtained in this work with excitation wavelength alteration permit us us to
suggest the new technique for discrimination between DOM and oil fluorescence. This technique
includes detection of two fluorescence spectra for investigated water sample using two
wavelengths of excitation, wich must be selected from above mentioned spectral range. The
spectral difference of these two fluorescence spectra has maximum at 340. ..360 nm, and is caused
by the fluorescence of oil pollutions dispersed in water. DOM or an oil film does not contribute in
this difference spectrum, if two excitation wavelengths are close enough one to another (their
variation must not exceed 15 nm).
For possible sources of light acceptable for this technique we can mark out the lines of Xe-
lamp for sample diagnostics, or some laser sources for remote sensing (for example, N2-laser with
337 nm and second harmonics of ruby laser with 347 nm of excitation). The suggested technique
for oil fluorescence separation has significant advantages comparatively to another possible
techniques. First, in this technique biological substances (amino acids, phenol compounds)
emitting at 340 nm with maximum of excitation spectra at 280 nm do not contribute in observed
fluorescence signal. It is very important, because when we use forth harmonics of YAG-laser (266
nm) for spectra excitation, the band at 340 nm in integral spectra is represented simultaneously by
oil pollution and biological organic substance.
Second, this technique using difference spectroscopy permits to avoid interference of
fluorescence of oil film from water surface, because spectral shape for oil films is independent of
excitation wavelength. This fact is very important, since fluorescence maximum of Diesel fuel is
located at 360 nm and its fluorescence interfere with that of oil pollution dispersed in water body
under the film.
4 - SYNCHRONOUS FLUORESCENCE SPECTRA AND THEIR APPLICATION FOR
OIL TYPE IDENTIFICATION
The Fig. 4 shows synchronous fluorescence spectra for oil pollutions in water using various
differencesAA between excitation wavelengthlex and emission wavelength Aem. As it is seen from
Fig. 4a, 4b, 4c, different types of oil pollutions correspond with different shapes of synchronous
fluorescence pectra. The synchronous spectra with aA= 50 nm are more intensive, and
informative comparatively to other spectra.
„Different types of oil pollutions in water sample can be distincted using synchronous
fluorescence spectra withAA=50 nm.
The comparasion of synchronous spectra for dissolved organic matter and for oils in water
shows the main difference between them (See Fig. 4a-c and 4d). Synchronous spectra for DOM
withAA=90 or 120 nm are very wide, and after normalizing by excitation source intensity do not
exhibit any structure. DOM practically does not contribute in synchronous spectra with a A=50 nm.
This corresponds with the described spectral behaviour of DOM with A. ex alteration. While 'Aex <
340 nm maximum of fluorescence is located at 440 nm. But when Aex > 340 nm the difference
between Aex and Aem exceeds 80 nm. Consequently, the detection of synchronous spectra with
aA= 50 nm permits to distinct oil pollutions in natural water with DOM.
Synchronous spectra for water sample just after and some time later after oil-water mixing
have some differences (See Fig. 4f). The intensity of line at 220 nm decreases. This spectral range
corresponds with fluorescence of light OP in water in emission spectrum with excitation at 220
nm. Two weeks after water sampling part of fight fraction of oil pollution evaporates. This appears
as decreasing of intensity of described band in synchronous spectra. So we can distinguish fresh
and old oil spills in water samples using synchronous spectroscopy.
The introduction of synchronous spectra in remote sensing meets some difficulties. However,
it is not necessary to detect the whole synchronous spectrum for oil identification. In laboratory
fluorescence study the key points of spectrum (values of Aex and Aem) could be obtained. The
