Analysis of aluminium in atmospheric aerosols in Bratislava using PIGE technique
Published in Acta Physica Universitatis Comenianae Volume LIV (2019) 115-121
Characterization of fine particles in the urban atmosphere is important for identification of pollutants. Since aluminium is most abundant metal in the Earth’s crust it can easily enter the atmosphere due to natural processes like soil resuspension, but also by anthropogenic activities like mining, agriculture and automobile industry. Aerosols sampled for radioactivity measurements were used for elemental analysis by PIGE (Particle Induced Gamma-ray Emission) technique.
There is a long tradition and experience at the Department of Nuclear Physics and Biophysics of the FMPI CU of atmospheric radioactivity monitoring in aerosols. The sampling device has been located next to the faculty building. Atmospheric air has been pumped with sampling rate of 80m3/h through 25 nitrocellulose membrane filters. These filters have been stacked next to each other covering area of approx. 0.5 m2. One of the 25 filters was separated and cut into half. Several ways for extraction of aerosols from the filter were tested. The best results were obtained with dissolved filters in methanol. Only inorganic fraction was separated and mixture of aerosols with 3% Formvar solution was used for thin sample preparation.
Energy of incident protons was 2.86 MeV (the highest cross section for 27Al(p, p’γ)27Al reaction with emission of 843 keV and 1013 keV gammas). Relative method using reference material was utilized to calculate the concentration of Al in the samples. 6 samples of filters were prepared and analysed. Some of the filters were previously analysed by the NAA (Neutron Activation Analysis) in Joint Institute for Nuclear Research in Dubna. Results from PIGE and NAA are compared in the table.
Concentrations of Al measured by PIGE and NAA technique | |||
|---|---|---|---|
| Filter | CAl PIGE (ng/m3) | St. deviation | CAl NAA (ng/m3) |
| A375 | 108 ± 12 | 8.8 | - |
| A401 | 58.5 ± 5.7 | 7.6 | - |
| A417 | 73.9 ± 8.4 | 7.6 | - |
| A426 | 155 ± 19 | 45.4 | 56.9 ± 1.7 |
| A430 | 124 ± 5 | 27.8 | 123 ± 4 |
| A434 | 132 ± 19 | 20.5 | - |
PIGE has proved to be useful tool to study light elements, like aluminum, in thin samples, while good agreement with NAA results was achieved. For our measurements, the detection limit is about 0.2 mg/g of Al in particulate matter, however by using more intensive proton beam, the limit could be lower. Next step in our research will be calibration of PIGE for other elements like fluorine and sodium.