Continuous measurements of near surface aerosols in the south-western European (Portugal) region in 2006–2008

Abstract. Scattering and absorption coefficients near the ground were measured in Évora, Portugal, in the period of 2006 to 2008. The average scattering coefficient, at the wavelength of 550 nm, for the whole period of measurements was found to be 40.3 Mm⁻¹ and the absorption coefficient, at the wavelength of 670 nm, 8.6 Mm⁻¹. These values are comparable to those measured in rural or background locations and reflect the small size of the city and relatively low magnitude of anthropogenic production at the site. A marked seasonal variation was found for the absorption coefficient, with a significant increase from 5.8 Mm⁻¹, in summer, to 13.4 Mm⁻¹, in winter. Regarding black carbon mass concentrations, this twofold increase, from 0.9 to 2.0 μgm⁻³, is mainly attributed to the wood combustion used for heating in conjunction with lower boundary layer mixing heights. The average scattering coefficient presented a more complex behaviour, although with a tendency for higher values in winter and lower values in spring.