Multiyear in-situ measurements of atmospheric aerosol absorption properties at an urban coastal site in western Mediterranean

Abstract

Abstract In-situ aerosol absorption properties measured in Valencia (Spain) for four years, from February 2011 to February 2015, have been analysed. Spectral absorption properties have been obtained using a seven-wavelength Aethalometer AE-31 which covers the range from UV (370 nm) to IR (950 nm). In order to obtain the absorption coefficients, compensation parameters have been calculated for the Aethalometer considering seasonal and spectral differences. For this multiyear measurement period, seasonal site-specific calibration parameters have been obtained. Furthermore, estimations of the absorption Angstrom Exponent (α abs ) have been calculated using the seven Aethalometer wavelengths. The averaged absorption coefficients (plus/minus the standard deviation) obtained for the seven channels range between 9 ± 4 Mm −1 at 950 nm and 33 ± 18 Mm −1 at 370 nm. These results are typical of a moderate polluted environment. The obtained absorption Angstrom Exponent (plus/minus the standard deviation) is 1.42 ± 0.08, which suggests the presence of brown carbon or black carbon coated by non-absorbing particles in our site. Seasonal and daily variations, together with the effect of both the boundary layer height and traffic, have been also studied. Strong seasonal differences in the absorption coefficient are found, mainly due to seasonal variation of the mixing layer height. On the opposite, the study of the diurnal variations of the absorption Angstrom Exponent proves that this parameter is more affected by traffic emissions than by the evolution of the mixing layer height.