Vertical characterization of fine and coarse dust particles during an intense Saharan dust outbreak over the Iberian Peninsula in springtime 2021
Authors: López-Cayuela María Ángeles , Córdoba-Jabonero Carmen , Bermejo-Pantaleón Diego , Sicard Michaël , Salgueiro Vanda , Molero Francisco , Carvajal-Pérez Clara Violeta , Granados-Muñoz María José , Comerón Adolfo , Couto Flavio T. , Barragán Rubén , Zorzano María-Paz , Bravo-Aranda Juan Antonio , Muñoz-Porcar Constantino , Costa María João , Artíñano Begoña , Rodríguez-Gómez Alejandro , Bortoli Daniele , Pujadas Manuel , Abril-Gago Jesús , Alados-Arboledas Lucas , Guerrero-Rascado Juan Luis 
Published: January 2023

Abstract. An intense and long-lasting Saharan dust outbreak crossed
the Iberian Peninsula (IP) from the southwest (SW) to the northeast (NE)
from 25 March until 7 April 2021. This work aims to assess the optical and
mass contribution of both fine and coarse dust particles along their
transport. Five Iberian lidar stations were monitoring the transport and
evolution of the Saharan dust particles, i.e. El Arenosillo/Huelva,
Granada, Torrejón/Madrid and Barcelona in Spain, and Évora in
Portugal. The particular meteorological conditions determined the aerosol
scenario along the overall dust event, differing in the first part of the
event (25–31 March), in which the strongest dust incidence occurred on 29–31 March at the south and central stations and 1 April at Barcelona, from the
second one (1–7 April). The use of the two-step POLIPHON algorithm showed
the relevance of using polarized lidar measurements for separating the
aerosol properties of dust fine and coarse particles as an added value.
Both the fine dust (Df) and coarse dust (Dc) components of the total
particle backscatter coefficient (total dust, DD = Dc + Df) were
separately derived. The dust plume was well-mixed with height and no
significant differences were found in the vertical structure of both the Dc
and Df particle backscatter coefficients. From the beginning of the dust
outbreak until 1 April, the vertical Df / DD mass ratio was nearly constant in time at each station and also in altitude with values of ∼ 10 %. Moreover, the mean dust optical depth at 532 nm was decreasing along that dust pathway, reporting values from SW to NE stations of 0.34 at El Arenosillo/Huelva, 0.28 at Granada, 0.20 at Évora, 0.28 at
Torrejón/Madrid, and 0.14 at Barcelona, although its Df / DD ratio remained almost constant (28 %–30 %). A similar pattern was found for the total dust mass loading and its Df / DD ratio, i.e. mostly decreasing mean mass values
were reported, being constant in its Df / DD ratio (∼ 10 %)
along the SW–NE dust pathway. In addition, the episode-mean centre-of-mass
height increased with latitude overall, showing a high variability, being
greater than 0.5 km at the southern sites (El Arenosillo/Huelva, Granada,
Évora) and ∼ 1.0 km at Torrejón/Madrid and Barcelona.
However, despite the relatively high intensity of the dust intrusion, the
expected ageing of the dust particles was hardly observed, by taking into
account the minor changes found in the contribution and properties of the
coarse and fine dust particles. This is on the basis that the IP is
relatively close to the Saharan dust sources and then, under certain dust
transport conditions, any potential ageing processes in the dust particles
remained unappreciated. The following must be highlighted: the different relative
contribution of the fine dust particles to the total dust found for their
optical properties (∼ 30 %) associated with the radiative
effect of dust, with respect to that for the mass features (∼ 10 %) linked to air quality issues, along the overall dust event by
crossing the IP.