Browsing by Author "Nunes, Teresa"
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- Aerosol optical properties at Santiago Island, Cape Verde.Publication . Cerqueira, Mário; Pio, Casimiro; Fialho, Paulo; Cardoso, João; Nunes, Teresa; Almeida, S. M.> huge amounts of mineral dust are emitted every year from the Sahara desert to the atmosphere; > optical parameters of mineral aerosols determine the direct interaction of solar and terrestrial radiation in the atmosphere through scattering and absorption; > mineral dust has a great impact on cloud formation leading to additional indirect radiation effects; > The dense haze from dust events is also known to affect visibility.
- 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.
- Seasonal Variability of Atmospheric Dust Over Cape Verde Islands.Publication . Pio, Casimiro; Freitas, Maria do Carmo; Cardoso, João; Nunes, Teresa; Almeida, S. M.; Almeida, Marta; Tchepel, O.; Rocha, F.; Cerqueira, Mário; Ferreira, F.; Terroso, D.; Fialho, Paulo; Dung, Ho; Custódio, Danilo
- Wet deposition of particulate carbon to the Central North Atlantic OceanPublication . Custódio, Danilo; Cerqueira, Mário; Fialho, Paulo; Nunes, Teresa; Pio, Casimiro; Henriques, DiamantinoElemental carbon (EC) and water-insoluble organic carbon (WIOC) concentrations were measured in wet-only precipitation samples collected on Terceira Island (Azores, Portugal) between December 2009 and October 2010, to investigate temporal variations, source regions and wet deposition fluxes. The global volume-weighted average (vwa) concentrations were 134 ± 19 μgC L(-1) for WIOC and 15.0 ± 1.6 μgC L(-1) for EC, which fall within the range of values that have been found in the European background atmosphere. The WIOC concentration exhibited a temporal variation over the study period with a minimum in winter (vwa 88 ± 16 μgC L(-1)) and a maximum in summer (vwa 477 ± 86 μgC L(-1)). This trend was due to the higher dilution effect of winter rains and possibly to an increase of biogenic particulate carbon incorporation during the growing season. A different temporal variation was observed for the EC concentration with a minimum in summer (vwa 4.2 ± 3.3 μgC L(-1)) and a maximum in spring (vwa 17.5 ± 2.2 μgC L(-1)). The observed trend was mainly related to changes in atmospheric circulation patterns over the Azores. A backward trajectory analysis was applied to identify possible source regions of particulate carbon. The highest WIOC and EC concentrations were associated with air masses that persisted for more than four days over the Central North Atlantic Ocean and with air masses arriving from Europe, respectively. Lower concentrations were observed in samples collected under the influence of back-trajectories from North America. Despite the lower abundance of particulate carbon, the wet deposition fluxes were higher for this group of samples, which reflects the higher amount of precipitation that is normally associated with air masses arriving in the Azores from the west and northwest sectors.