Naslov
Quantitative analysis of cascade impactor samples - revisited

Autori
Orlić, Ivica ; Chiam, S.Y. ; Sanchez, J.L. ; Tang, S.M.

Izvornik
Nuclear Instruments and Methods in Physics Research. B (0168-583X) 150 (1999), 1/4; 465-469

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
aerosols; pollution; cascade impactor; Thick target correction factor

Sažetak
Concentrations of aerosols collected in Singapore during the three months long haze period that a€ected the whole South-East Asian region in 1997 are reported. Aerosol samples were continuously collected by using a fine aerosol sampler (PM2.5) and occasionally with a single orifice cascade impactor (CI) sampler. Our results show that in the fine fraction (<2.5 um) the concentrations of two well-known biomass burning products, i.e. K and S were generally increased by a factor 2-3 compared to the non-hazy periods. However, a discrepancy was noticed, at least for elements with lower atomic number (Ti and below) between the results obtained by the fine aerosol sampler and the cascade impactor. Careful analysis by means of Nuclear Microscopy, in particular by the Scanning Transmission Ion Microscopy(STIM) technique, revealed that thicknesses of the lower CI stages exceeded thick target limits for 2 MeV protons. Detailed depth profiles of all CI stages were therefore measured using the STIM technique and concentrations corrected for absorption and proton energy loss. After correcting results for the actual sample thickness, concentrations of all major elements (S, Cl, K, Ca) agreed much better with the PM2.5 results. The importance of implementing thick target corrections in analysis of CI samples, especially those collected in the urban environments, is emphasized. Broad beam PIXE analysis approach is certainly not adequate in these cases.

Izvorni jezik
Engleski

Znanstvena područja
Fizika

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