Seven years of measurements of aerosol scattering properties, near the surface, in the southwestern Iberia Peninsula 1Évora Geophysics Centre, Évora, Portugal
2Physics Department of the University of Évora, Évora, Portugal
Received: 19 Apr 2010 – Published in Atmos. Chem. Phys. Discuss.: 01 Jun 2010 Abstract. Aerosol scattering properties, near the surface (at about 10 m
height), were measured during a period of seven years (2002–2008)
at Évora, Portugal. The average (and median) scattering and
backscattering coefficients, at the wavelength of 550 nm, were
found to be 42.5 Mm−1 (29.9 Mm−1) and 5.9 Mm−1
(4.4 Mm−1), respectively. Also, the average and median
scattering Ångström exponent (1.4 and 1.5) indicate that
scattering was, in general, dominated by sub-micrometer particles.
Both seasonal and daily cycles are shown, which were related to
local production and transport of particles from elsewhere. Summer
and winter average values of the scattering coefficient, at the
wavelength of 550 nm (47 and 54 Mm−1, respectively),
correspond to a significant increase in the aerosol particle
concentration when compared with spring and fall (35 and
37 Mm−1, respectively). Also, the average increase in the
Ångström exponent for summer and winter seasons is
consistent with the input of sub-micrometer particles from
anthropogenic origin in winter and forest fires in summer.
Revised: 19 Nov 2010 – Accepted: 22 Nov 2010 – Published: 03 Jan 2011
Back-trajectory analysis indicated that the site was regularly under the
influence of air masses from the Atlantic area, with low particle loads (low
scattering coefficients), but as the influence of transport from the
continent (Iberia Peninsula) increased, the aerosol particle load was
observed to increase as well as the relative importance of fine particles
over coarse ones, approaching the features observed at the site during
European air masses influence.
Citation: Pereira, S. N., Wagner, F., and Silva, A. M.: Seven years of measurements of aerosol scattering properties, near the surface, in the southwestern Iberia Peninsula, Atmos. Chem. Phys., 11, 17-29, doi:10.5194/acp-11-17-2011, 2011.