CHAPTER 19 • PIXE Analysis for Trace Elements in Marine Environments
der of 1 Ilm, in two orthogonal directions or in linear scanning. A PIXE spectrum is
recorded at each position.
Given its spatial resolution, the microbeam is not comparable with the electron
microprobe resolution in surface analyses, while it is preferable for target thicker
than some tens of micrometers, because the proton microbeam resolution is mantained
(1-2Ilm) for tens of micrometers of penetration delth.
The micro-PIXE sensitivity is of the order of 10 - g g -1 of the exposed target. Given
the small size of the exposed area (few micrometers diameter), the detection of absolute quantities of 10- 16 g are allowed. The energy of the proton beam (some MeV) permits the detection of heavy elements by means of K lines. This sensitivity represents
an advantage in trace element analysis with respect to the electron microprobe capabilities (10- 3 g g -1).
The application of micro-PIXE in the environmental field may be addressed to the
investigation of major and trace elements in aerosol particles (such as marine aerosols), providing maps of a portion of an aerosol deposit on a thin backing. This technique is obviously not adequate for the examination of water samples, while it finds
wide application in geology, for the immediate irradiation of slices of rocks and minerals.
19.6
PIXE Application in the Study of Pollutant Enrichment in
Marine Aerosols
Long-range pollutant transport is of global importance in environmental research.
Marine aerosol is a matrix strongly involved in exchange of substances between sea
and atmosphere and in their further transfer to coastal areas, where, for example, vegetation damage may occur. It is also well known that, under favourable meteorological conditions, the finest fraction of aerosols may be transported far from the source
to remote areas.
In the study of marine aerosol the role of many natural and man-made surfactants
that spontaneously segregate at the sea surface-air interface has to be estimated. The
marine aerosol is mainly generated by breaking wave events (Resch 1986). Air bubbles
trapped by breaking waves, during the wave rolling motion, are particularly enriched
in soluble surfactants. Marine spray is produced by the breaking of these bubbles, when
they rise again at the sea surface. The bubble collapse involves films and jet formation
(Blanchard 1975), particularly enriched of soluble surfactant matter. The jet microdrops
are injected in the air at high levels (6-15 cm), with high probability of long life in the
atmosphere. Recent studies (Cini et al. 1994) proposed a model of the enrichment partition of the surfactants in the jet drops, and the finest drops were shown to be the
more enriched. The surfactant ability to interact with inorganic ions induces pollutant adsorption and their further long-range transport by means of jet drops.
The PIXE analysis of aerosol samples may be a very useful tool to better understand these processes, given the PIXE capability to detect the pollutant elements scavenged by the surfactants enriched in the aerosol jet drops.
An experiment is in running, in order to validate the model of the enrichment partition of the surfactants in the jet drops. The first step, performed up to now, consisted
of analysis of samples obtained from an apparatus for artificial production of aerosol
der of 1 Ilm, in two orthogonal directions or in linear scanning. A PIXE spectrum is
recorded at each position.
Given its spatial resolution, the microbeam is not comparable with the electron
microprobe resolution in surface analyses, while it is preferable for target thicker
than some tens of micrometers, because the proton microbeam resolution is mantained
(1-2Ilm) for tens of micrometers of penetration delth.
The micro-PIXE sensitivity is of the order of 10 - g g -1 of the exposed target. Given
the small size of the exposed area (few micrometers diameter), the detection of absolute quantities of 10- 16 g are allowed. The energy of the proton beam (some MeV) permits the detection of heavy elements by means of K lines. This sensitivity represents
an advantage in trace element analysis with respect to the electron microprobe capabilities (10- 3 g g -1).
The application of micro-PIXE in the environmental field may be addressed to the
investigation of major and trace elements in aerosol particles (such as marine aerosols), providing maps of a portion of an aerosol deposit on a thin backing. This technique is obviously not adequate for the examination of water samples, while it finds
wide application in geology, for the immediate irradiation of slices of rocks and minerals.
19.6
PIXE Application in the Study of Pollutant Enrichment in
Marine Aerosols
Long-range pollutant transport is of global importance in environmental research.
Marine aerosol is a matrix strongly involved in exchange of substances between sea
and atmosphere and in their further transfer to coastal areas, where, for example, vegetation damage may occur. It is also well known that, under favourable meteorological conditions, the finest fraction of aerosols may be transported far from the source
to remote areas.
In the study of marine aerosol the role of many natural and man-made surfactants
that spontaneously segregate at the sea surface-air interface has to be estimated. The
marine aerosol is mainly generated by breaking wave events (Resch 1986). Air bubbles
trapped by breaking waves, during the wave rolling motion, are particularly enriched
in soluble surfactants. Marine spray is produced by the breaking of these bubbles, when
they rise again at the sea surface. The bubble collapse involves films and jet formation
(Blanchard 1975), particularly enriched of soluble surfactant matter. The jet microdrops
are injected in the air at high levels (6-15 cm), with high probability of long life in the
atmosphere. Recent studies (Cini et al. 1994) proposed a model of the enrichment partition of the surfactants in the jet drops, and the finest drops were shown to be the
more enriched. The surfactant ability to interact with inorganic ions induces pollutant adsorption and their further long-range transport by means of jet drops.
The PIXE analysis of aerosol samples may be a very useful tool to better understand these processes, given the PIXE capability to detect the pollutant elements scavenged by the surfactants enriched in the aerosol jet drops.
An experiment is in running, in order to validate the model of the enrichment partition of the surfactants in the jet drops. The first step, performed up to now, consisted
of analysis of samples obtained from an apparatus for artificial production of aerosol