The use of Nuclear reaction analysis technique for the determination of Nitrogen in aerosol samples collected on teflon filters

Ion Beam Analysis (IBA) techniques are very suitable for non-destructive characterization of atmospheric particulate matter. The most used for this purpose is Particle Induced X-ray Emission (PIXE) thanks to its ability to detect a wide range of elements (Z>10) simultaneously with higher sensitivity than other IBA techniques. Nevertheless, the determination of light elements content, as C, N, O and H, is of crucial interest, as these elements constitute a big amount of the aerosol composition. These elements are not detectable by PIXE because of the selfabsorption of their characteristic X-rays in the sample itself and in the detector window. A method has been developed to measure light elements in aerosol particulate matter collected on Teflon (CF2) filters by Elastic Backscattering Analysis (EBS) and Particle Elastic Scattering Techniques (PESA) with proton beams (Chiari, 2004, Chiari, 2005). Quantitative results have been obtained for these light elements with very satisfactory accuracies for C, and some less for O and especially for N. In this work, Nuclear Reaction Analysis (NRA) has been used as an alternative IBA technique for N determination in aerosol samples collected on Teflon, namely exploiting the reactions 14N(d,α0)12C and 14N(d,α1)12C. The high Q-values of these reactions avoid the interferences between the reaction products and the backscattered beam particles. NRA measurements have been performed at the 3 MV Pelletron accelerator of the CNA in Seville on a set of PM10 and PM2.5 samples with beams of deuterium of 1.9 MeV energy and a detection angle θ = 150º, which corresponded to the optimal measurement conditions. As can be seen in Figure 1, the signal peak from the 14N(d,α0)12C reaction appears in a background-free region of the spectrum thus allowing Nitrogen determination without interferences from filter or other aerosol components. Absolute N concentrations were obtained by normalization to thin reference standards containing known areal density of Nitrogen, with an overall uncertainty of about 4-8%. Typical minimum detection limit (MDL) for N is 0.1 μg/cm2, corresponding to 0.02 μg/m3 considering a 47 mm diameter Teflon filter and sampling for 24 hours at 2.3 m3/h (EN12341 European standard). The samples have been analysed also by EBS at the 3 MV Tandetron accelerator of the LABEC laboratory of INFN in Florence, using proton beams of 3.6 MeV energy and a scattering angle of 150°. The total N content obtained by the different IBA techniques is comparable, nevertheless EBS provides about 20% more Nitrogen concentration than NRA. Then the organic component of Nitrogen can be obtained from the total N concentrations measured by NRA as the amount in excess of “ammonium N” and “nitrate N”, being in our situation negligible the contribution from nitrites. In PM10 samples “organic N” resulted about 40% of total Nitrogen, while this fraction decreased to about 25% for PM2.5 samples. This work has been supported by INFN (NUMEN project) and by the Spanish Ministry of Education and Science (MEC). Chiari, M., Del Carmine, P., Lucarelli, F., Marcazzan, G., Nava, S., Paperetti, L., Prati, P., Valli, G., Vecchi, R., Zucchiatti,A.,2004. Atmospheric aerosol characterisation by Ion Beam Analysis techniques: recent improvements at the Van de Graaff laboratory in Florence. Nucl. Instr. and Meth. B 219–220, 166-170. Chiari, M., Lucarelli, F., Mazzei, F., Nava, S., Paperetti, L., Prati, P., Valli, G., Vecchi, R.,2005. Characterization of airborne particulate matter in an industrial district near Florence by PIXE and PESA. X-Ray Spectrometry 34, 323-329.