GISdevelopment.net ---> AARS ---> ACRS 1991 ---> Poster Session 2

Laser diagnostics of natural dissolved organic matter and oil-products in water

Svetlana V. Patasayeva, Victor V. Fadeev, Elena M, Filippova, Vasily V. Chubarov
Physics Department, Moscow State University
Moscow, 119899 USSR


Abstract
In this work spectral study of water samples with dissolved organic matter (DOM) and different oil-products (OP) has been carried out. For separation of DOM and OP fluorescence signals emission (lexe - 266 nm) and excitation spectra acquisition has been realized. Temperature variations and UV irradiation influence on fluorescence spectra of water samples have been investigated.
Study of fluorescence synchronous, excitation and emission (with lamp and laser excitation source) spectra of different OP in water, in hexane solutions and in hexane extract from water and in hexane extracts from water samples have been carried out in this work. Hexane solutions and extracts from water samples give similar fluorescence excitation and synchronous spectra for the same type of OP. This gives possibility for rough identification of OP in water samples and proves hexane-extract technique for oil quantity diagnostics.
The obtained results give a chance to develop the remote method of oil and OP diagnostics in water.

Introduction
Currently fluorescent methods are widely applied for environment control including organic pollutions measurement in water. The basic principle of remote fluorescence sounding is a use of Raman Water Scattering signal as an intrinsic standard (1-2).

Remote diagnostics of organic pollutions from the shipboard by N2-laser (lexc = 337 nm) using a technique of standardizing of fluorescence spectrum by water Raman signal has been but into practice in Indian Ocean in 1984-1985(1). Spectra were detected by optical multichannel analyzer (OMA-1). Tests have showed that for the Remote monitoring of pollution florescence during daytime the gating needs to be less than 50 ns.

The most difficult problems arising during fluorescent monitoring of natural sea and river water are: 1) Spectral separation of dissolved organic matter (DOM) and OP concentration have been carried out in this work. Emission, excitation and synchronous fluorescence spectra were detected by the lamp spectro fluorimeter "Jobin Yvon 3CS", with computer data handling and correction for instrumental spectral sensitivity. Also we used N2 - laser (lexc = 337 um) and fourth harmonic of YAG-laser (lexc = 266um) for fluorescence excitation.

Temperature influence on Florescence Spectra of Dom in water
  1. At temperature rise from 0°C to 80°C intensity for excitation and emission DOM fluorescence spectra decreases. Temperature decrease leads to inverse effect.
  2. Valuable changes of fluorescence intensities don't lead to spectral shape changes (location of spectral maxima and spectrum width).
  3. Temperature dependence of spectral intensity is a reversible process with accuracy + 4%.
  4. Temperature dependence of maximum intensity both for emission and excitation spectra is well described by the formula I=I0exp -a (t-t0)), where sing "0" corresponds to temperature t = 20°C. Coefficients a = 0.0082 has been obtained for emission spectra and a=0.0078 for excitation spectra.
Thus temperature influence on Dom fluorescence spectra in natural water is enough small and may be easy taken into account during in situ measurement of Dom concentration using correction factor.

Ultraviolet Irradiation Influence on Dom Fluorescence spectra
In this work the samples of DOM from Baltic Sea were irradiated evenly in volume in 1 cm quarts cell by Hg-lamp and Xe-lamp with different color glass filters and interfilters.
  1. The strongest influence on spectra appears as a result of shortwave UV radiation (l200….300 nm): spectra are distorted by shape, maxima o excitation and emission spectra shift to longer wavelengths (Dl for emission spectra < 10 nm and Dl for excitation spectra < 15-25 nm, depends from irradiation time). UV light in 300 …. 325 range effects on DOM fluorescence spectra like as wavelength (325….400 nm) leads to intensity and width decrease but does not effect any spectrum maxima shift. Visible light does not affect any DOM spectra characteristics.
  2. The spectral range of maximal intensity changes in excitation spectra approximately equals to that of irradiation. Thus if water sample is irradiated by sun light (l>300nm) changes of fluorescence maximum intensity with lexc = 337 nm would be much than with lexc <300 nm.
  3. Absorption spectra failed to reveal any correlation with UV irradiation. It was obtained also that there is no correlation between absorption and fluorescence spectra behaviour, it is an accordance luminescence part of DOM does not contribute much in absorption spectrum.
  4. UV radiation affect unreversibly all spectral characteristics (investigation time was 3 days).
During in situ monitoring UV sun irradiation of surface water leads to errors of Dom concentration measurement (up to 50% using lexc = 337 nm), yet we can't calculate this natural factor. Errors could be decreased using shorter lexc (for example lexc = 266 nm).

Oil and oil products fluorimetry in water
The method of oil and OP diagnostics in water using hexane-extract technique has been described in (2). However direct OP measurement in water by fluorescence spectra is connected with some difficulties (4): overlapping of OP and DOM spectra, existence of OP in water in different forms (dissolved, dissolved-emulgated and oil film). It makes of fluorescence against OP concentration difficult.

Fluorescence excitation, synchronous and emission spectra investigations of different OP I water, in hexane and in hexane extract from water samples have been carried out in this work.
  1. Excitation spectra show a principal distinction between OP and DOM fluorescence signal. The biggest distinction is in distinction is in spectral range 230…..270 nm. So for spectral separation of DM and OP in water we can measure fluorescence spectrum using lexc = 230..270 nm.
  2. Hexane solutions and extracts from water samples gives similar fluorescence excitation and synchronous spectra for the same type of OP. This proves hexane-extracts fluorescent technique of OP diagnostics in water samples.
  3. Hexane extracts or water samples of different OP types are unlike in spectral shape (excitation and synchronous spectra), so a rough identification of OP in water samples is possible. Fluorescence emission spectra of hexane extracts with (lexc = 266 nm) consist of 3 bands with maxima at 315 + 5, 353 + 2 (the most intensive), 385 + 5 nm. The intensity ratio of these bands can be used for OP diagnostics in water samples.
  4. One of the fluorescence maxima of OP in water is placed about 330 nm using shortwave excitation (lexc = 266nm). So for some water samples from the black sea and Moscow-river fluorescence intensity at 330nm (lexc = 266 nm) was compared with OP concentration from hexane - extracts technique. The correlation was noticeable but not complete because of presence some biological organic substances giving rise to fluorescence at 330 nm. As our tests show one needs not to use lexc = 250 ….280 nm to avoid fluorescence of biological matter.

Fig. 1 Fluorescence spectra (lexc = 266 nm, fourth harmonic of YAG-laser) of two water samples from the black seas (expedition on August 1991) surface water sample and water from depth 200m.

Concentration of organic carbon is equal correspondingly to 4.0 and 5.6 mg/I

The band at 290 nm s Raman scattering of software.

The obtained results give a chance of develop the Remote methods of oil and OP diagnostics in water. Now we can detect probable location of oil-products in very low concentration direct in water using UV excitation sources. It is possible to identificate different oil pollutions in water samples using synchronous or excitation spectra and measure OP concentration in water using hexane-extract technique.

References
  • Chubarov V.V. Organic pollutions measurement in water in laser fluorescence method using Raman scattering as an internal standard //Dessert . for candidate degree. Moscow state university (USSR). 1984.
  • Fadeev V.V. Laser spectroscopy of aquatio media . //Dissertation for doctor Degree. Moscow State University (USSR). 1993.
  • Schifrin KS. Introduction into oceanoptics. //Leningrad: Gidrometeoizdat (USRR). 1993.
  • Abroskin A.G. Nolde S.E., Fadeev V.V. //Sov. Phys.-Dokl.. 1988.V.33.N3 215-217.