Fingerprinting techniques sources

It is apparent that these "fingerprint techniques relating particle sizes as well as concentration data to source components need further refining. However, it should be possible eventually to identify the origin of airborne particles provided suflBcient chemical data become available. Recently, lead isotopic ratios have been used to estimate the contribution of blood lead levels originating from gasoline combustion. Perhaps this approach can be further refined to better characterize the sources of other airborne metals. 

If the source fingerprints, for each of n sources are known and the number of sources is less than or equal to the number of measured species (n < m), an estimate for the solution to the system of equations (3) can be obtained. If m > n, then the set of equations is overdetermined, and least-squares or linear programming techniques are used to solve for L. This is the basis of the chemical mass balance (CMB) method (20,21). If each source emits a particular species unique to it, then a very simple tracer technique can be used (5). Examples of commonly used tracers are lead and bromine from mobile sources, nickel from fuel oil, and sodium from sea salt. The condition that each source have a unique tracer species is not often met in practice. 

The high spatial resolution of the technique enables identification of a source of contamination by the characteristic fingerprint left on the wafer. This is illustrated in Fig. 10.5, which shows lifetime maps of wafers contaminated in different ways. The concentric circles shown in Fig. 10.5 a are caused by oxygen precipitates. The... 

ToF-SIMS analytical techniques for characterizing human hair surfaces using Ga+ and primary ion sources have been compared.84 Similar hair fingerprints were obtained with both ion sources. With the Cg0 ion source, on average, secondary ion intensities between two and three orders of magnitude higher than the Ga+ primary ion source were observed.84... 

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