A new method combining the pattern recognition (PR) technique with micro-PIXE spectrum was used for direct assessment of lead pollution in the atmosphere of Shanghai City. Single aerosol particles (SAP) of PM 10 (<10 µm) were analyzed using the nuclear microprobe. Every particle is characterized with its micro-PIXE spectrum, which can be considered its fingerprint. The PR technique was applied to trace a lead contaminated aerosol particle back to its source. The discrimination of different pollutant sources was enhanced with investigating the individual aerosol particles. The results showed that the lead contamination from automobile exhaust should not be neglected. The lead concentration with low level was detected in most unleaded gasoline particles; however, the highest lead level of 1500 ppm was found in one of them. Furthermore, four other main pollutant sources contributing to the lead contamination in the Shanghai atmosphere were clearly identified by this method. They are the cement industry, the coal combustion, the oil combustion, and the metallurgic industry. Some other unidentified particles suggested that some more lead emitters might also exist in Shanghai.
In order to identify the sources of individual aerosol particles, we developed an identification system based on the combination of the micro-PIXE (particle-induced X-ray emission) technique with the pattern recognition (PR) technique. It uses the micro-PIXE spectrum of an individual aerosol particle as its fingerprint to identify the origin of the particles. A total of 294 micro-PIXE spectra of individual aerosol particles, collected at Shanghai City in China, were applied to test the PR system. These particles were collected from several pollution sources and a local environment monitor site. Most of the environment particles were identified, and the most probable sources were assigned by the PR system. It was found that cement factories and vehicle exhaust are the major contributors. About 14% of the particles from the environment monitor site could not be identified by their spectra. They might have come from some other sources we have not yet investigated. The validity and the efficiency of the system are evaluated and discussed. It is demonstrated that the combination of micro-PIXE with the pattern recognition technique offers a new, powerful tool for the source identification of individual aerosol particles.
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