Browsing by Author "Reis, M. A."
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- Analysis of Atmospheric Aerosols Using the Lisbon Nuclear MicroporePublication . Rita, E. M.; Alves, L. C.; Reis, M. A.; Rodrigues, A. F.; Fialho, Paulo; Soares, J. C.The nuclear microprobe installed at Instituto Tecnológico e Nuclear, in Lisbon, was used in the analysis of aerosols collected at the Azores islands. Samples from two different aerosol groups were analysed. One referred to aerosols that were carried from North America and the other one contained aerosols that were carried from the Sahara desert and crossed over Europe. Coarse and fine fractions were analysed for each aerosol group and two-dimensional elemental maps were constructed, which allowed the identification of several individual particles. For particles of interest, elemental spatial correlations and dimensions were determined and point analysis was also carried out (depth information was achieved by fitting Rutherford backscattering spectra). Some of these particles are quite interesting. For instance, in the fine fraction of the aerosols that were carried from North America, particles were found with Cu and Cl in the atomic proportion 1:2 and with dimensions 15 x 15 x 15 μm³, and in the corresponding coarse fraction a particle with K and S was identified, with dimensions 28 x 35 x 30 μm³. Some differences were found between the aerosols groups. One example of these are Ti particles (fine fraction) and Rb (coarse fraction) that were identified in one group (Sahara desert and Europe), but not in the other.
- The application of a multi-wavelength Aethalometer to estimate iron dust and black carbon concentrations in the marine boundary layer of Cape VerdePublication . Fialho, Paulo; Cerqueira, Mário; Pio, Casimiro; Cardoso, João; Nunes, Teresa; Custódio, Danilo; Alves, Célia A.; Almeida, S. M.; Almeida-Silva, M.; Reis, M. A.; Rocha, F.The two-component model (Fialho et al., 2006) was used to decouple the contributions of black carbon (BC) and iron oxides, present in dust, to the aerosol attenuation coefficient, measured with a multiwavelength Aethalometer. The model results were compared with the elemental carbon (EC) and iron concentrations determined in the laboratory from the analysis of aerosol particles collected with conventional samplers. The comparison was based on one year of data obtained at Praia, Santiago Island, Cape Verde, after side by side operation of the aerosol monitoring instruments. The linear regression equation that best describes the relationship between BC concentrations, derived from the Aethalometer, and EC concentrations, derived from a PM10 high-volume sampler after filter analysis with a thermal optical method, presents a slope of 1.01 ± 0.05 and a correlation coefficient (r) of 0.90, showing that the model worked as intended to describe BC concentrations without interferences from iron dust. On the other hand, the linear regression equation that best describes the relationship between the iron concentrations derived from the Aethalometer and elemental iron concentrations, derived from a PM10 lowvolume sampler after filter analysis by k0 e Instrumental Neutron Activation Analysis, presents a slope of 0.495 ± 0.014 and a correlation coefficient (r) of 0.96. These results show that the two-component model underestimated the iron concentrations in dust aerosol, which was explained by differences in the size range of particles sampled with the Aethalometer and the PM10 low-volume sampler together with differences in the size distribution of iron oxides.
- Comparison of continental Portugal and Azores Islands aerosol during a Sahara dust stormPublication . Reis, M. A.; Oliveira, O. R.; Alves, L. C.; Rita, E. M.; Rodrigues, Félix; Fialho, Paulo; Pio, Casimiro; Freitas, Maria do Carmo; Soares, J. C.Airborne particulate matter plays an important role in the Earth's energy balance. One of the main reasons is that the real size of a significant number of the particles, mainly those of anthropogenic origin, is similar to the wavelength of visible light. Knowledge of the composition of such particles, as well as their dynamics and trajectories in the atmosphere is therefore very important. In the period from 23 February to 22 March 2000, a movement of airborne particulate matter going over Europe and towards Azores was identified based on satellite observation. This work presents a preliminary study based on PIXE and nuclear micro-probe analysis of samples collected during that period both in Portugal mainland and in Terceira Island in the Azores. Time-shifted correlation of sample composition and individual particle composition are presented and discussed. Results point to the possibility of inferring long-range transport of aerosol particles from the samples multi-element analysis, and to the existence of fractions of the North Atlantic aerosol identical at both Portugal mainland and Terceira Island.