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- Nelson, J William, et al.
(författare)
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Aerosol Composition Studies Using Accelerator Proton Bombardment
- 1974
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Ingår i: Proceedings of "Third Conference on Application of Small Accelerators". ; 1, s. 139-147
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Konferensbidrag (refereegranskat)abstract
- The proton beam of the Florida State University Tandem Van de Graaff Accelerator is being used to make quantitative determinations of the composition of particulate matter found in the atmosphere. Proton scattering using 16 MeV incident particle energy is employed to resolve the light elements (up to Cl), while elements Al and heavier are observed via proton induced X-ray emission analysis. In order to realize advantages of these proton excited analyses, specialized techniques are used, such as the use of uniform beams which entirely cover the area of targets of non-uniform areal density. Also, specialized air sampling equipment has been built to take advantage of the small size of samples required for proton induced analyses. The multielement character, ease of automation, and short time (several minutes) needed for analysis make these techniques attractive from the standpoint of analysis cost per sample.
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| 2. |
- Winchester, John W, et al.
(författare)
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Trace Metals in the St. Louis Aerosol
- 1974
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Ingår i: Proceedings of the Second International Conference on Nuclear Methods in Environmental Research. ; , s. 385-394
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Konferensbidrag (refereegranskat)abstract
- The elemental composition of the St. Louis aerosol has been investigated at rooftop sites in south and central locations in the city as part of the August, 1973 field season of the Regional Air Pollution Study of the U.S. Environmental Protection Agency. Sampling by 5-stage cascade impactor with backup filter permits analysis by proton-induced x-ray emission (PIXE) of size fractions of aerodynamic diameter >4, >2m >1, >0.5, >0.25, <0.25µm for elements 16S to 35Br by K x-ray detection and 82Pb by L x-rays. The aerosol study indicates the following: 1. Particle size distributions of S, Cl, K, Ca, Ti, V, Mn, Fe, Cu, Zn, Br, and Pb can be measured in samples from 0.7 m3 of air collected over 12-hour intervals at 1 liter/min flow rate, with precision of single analyses generally 10-30%, except near the nanogram detection limit. 2. Some elements, e.g. Ca, Fe, Ti, K show a tendency for highest concentrations in air measured in largest particle size fractions, and the pattern of distribution of concentration with size is relatively invariant. Predominantly dispersion source processes may account for their entry into the atmosphere. 3. Other elements, e.g. S, Pb, Zn, have substantial proportions of their atmospheric concentrations on smallest particles and show greater variability in particle size distribution patterns, suggesting aerosol formation processes of vapor condensation at high or low temperatures. 4. During 16-22 August 1973 an atmospheric change occurred from a period of low speed and mostly southerly air flow, with evident haze and air pollution, to higher speed and westerly shifting to easterly air flow, with improved visibility and air quality. The change was associated with drops in concentrations of Ti, Fe, Ca, K, and S but not Zn or Pb at the south site and Ti but not the other elements at the central site. Transport of air pollution from industrial sources south of the city is indicated. 5. The central site showed diurnal variation during the first period where concentrations of Ti, Fe, Ca, K, and S were higher in samples taken from midnight to noon than in those from noon to midnight. Variations were greatest for intermediate sized particles.
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