Departamento de Física
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Browsing Departamento de Física by Subject "Absorption coefficients"
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- An integrating sphere spectral system to measure continuous spectra of aerosol absorption coefficientPublication . Montilla, E.; Mogo, Sandra; Cachorro, Victoria; De Frutos, Ángel MAn integrating sphere spectral system has been developed that allows the measurement of continuous spectra of light absorption coefficients, saðlÞ of atmospheric aerosols. This system is based on the filter attenuation method covering the spectral wavelength range 320–800 nm with a variable spectral resolution. The sample filters had to be diluted in chloroform previous to the light attenuation measurements and hence the system cannot measure continuously but only on the basis of daily sampling. The system was calibrated using known amounts of absorbing and non-absorbing industrial substances at relevant atmospheric absorption levels. The resulting values of sa ðlÞ were compared with those delivered by a commercial photometer (particle soot absorption photometer) in the laboratory and also with field measurements, with a maximum discrepancy of 12.5% for atmospherically relevant values. The measurement uncertainty of the integrating sphere system is about 10% maximum. The importance of obtaining continuous spectral data is the possibility to determine the Ångström absorption exponent, aa , in different spectral ranges, including the UV. This exponent can then be used to help in obtaining the aerosol composition information.
- In situ UV-VIS-NIR absorbing properties of atmospheric aerosol particles: Estimates of the imaginary refractive index and comparison with columnar valuesPublication . Mogo, Sandra; Cachorro, Victoria; de Frutos, Ángel MIn this work, a novel technique is used to estimate the aerosol complex index of refraction of in situ collected samples. Samples of atmospheric particulate matter were collected in El Arenosillo, southern Spain, on polycarbonate filters during summer 2004 as part of an aerosol characterization campaign. These samples were analyzed for the volumetric absorption coefficient in the 320e800 nm spectral region and an estimation of the effective imaginary refractive index was made. The values of the imaginary part of the complex refractive index ranged between 0.0009e0.0215 at 800 nm and 0.0015e0.0114 at 320 nm. Little dependence on the wavelength was observed. Several intense and long lasting desert outbreaks were registered during the campaign and the complex refractive index almost doubles its value during these dust events. Finally, we present a comparison of data obtained in situ with columnar data obtained from the AERONET network. A correlation factor of 0.64 was obtained between both data, which gives an idea of how accurately the in situ ground data represent the total column.