Browsing by Author "Hansen, Anthony"
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- Absorption coefficients by aerosols in remote areas: a new approach to decouple dust and black carbon absorption coefficient using seven-wavelength Aethalometer dataPublication . Fialho, Paulo; Hansen, Anthony; Honrath, RichardWe present a new approach to decouple aerosol absorption coefficients due to iron oxide in Sahara dust from those due to black carbon (BC) particles. Absorption coefficients, σaerosol(λ,t), were measured at the summit of Pico mountain (2225 m ASL) in the Azores Islands using a seven-wavelength Aethalometer. Measurements between 27th July and 1st August, 2001, are analyzed here. Variations in aerosol absorption coefficients were uncorrelated to those of CO during the latter part of this period, suggesting the presence of non-combustion-derived aerosol, apparently African dust. To differentiate between BC and other absorbing particles, we analyzed the wavelength dependence of σaerosol(λ,t) and determined a best-fit exponent during the later period equal to -2.9±0.2, somewhat lower than previously reported for soil dust. Using this method, it is possible to estimate the aerosol absorption due to BC and that due to soil dust separately through the full period analyzed.
- Identification of black carbon and dust aerosol events at the Azores PICO-NARE station during the ICARTT experiment.Publication . Fialho, Paulo; Barata, Filipe; Honrath, Richard; Hansen, AnthonyDuring the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) experiment (July – August 2004), aerosol samples were taken and their aerosol absorption coefficients measured. At the same time the levels of carbon monoxide and ozone where also monitored. These measurements were taken at PICO-NARE site on Pico mountain summit (2225 m ASL) in the Azores Islands. This site is in the pathway of air masses that travel from the surrounding continents (Africa, Europe and North America) that carry with them, among other species, aerosols resulting from combustions (black carbon) and/or natural emissions (dust). In particular, transport from Africa may bring soil dust particles, rich in iron oxides, which are involved in the biogeochemical cycling of iron, an essential micronutrient to marine phytoplankton (Arimoto, Balsam, & Schloesslin, 2002). During this period the sampled masses mainly came form the North American and during sometimes carried with them pollutants resulting from forest fires that occurred in Canada and Alaska.
- The Aethalometer calibration and determination of iron concentration in dust aerosolsPublication . Fialho, Paulo; Freitas, Maria do Carmo; Barata, Filipe; Vieira, Bruno; Hansen, Anthony; Honrath, RichardThis paper shows the use of the instrumental neutron activation analysis (INAA) technique to calibrate Aethalometer instruments’ response to iron oxides present in Saharan dust aerosol. The five samples selected for this calibration were collected with a seven-wavelength Aethalometer (model AE31) at the summit of Pico mountain (2225 m ASL) in the Azores Islands. These samples correspond to measurements taken between the 31 October and 5 November, 2001. Analysis of these samples by the INAA technique gave a total mass of 14.84 ± 0.70 μg (Fe). Correlation of the analytical results with the optical measurements allowed the determination of the elemental iron calibration constant, KFe (0.234 ±0.022 μm4 m² gˉ¹), which can be used in the determination of iron concentrations from multi-wavelength Aethalometer measurements. As an example of this, we used Aethalometer measurements during the 2001 event to calculate hourly average dust iron, 〈CFe〉, concentrations, which range from 0.00 and 1.77 μg (Fe) mˉ³.