Vertical characterization of fine and coarse dust particles during an intense Saharan dust outbreak over the Iberian Peninsula in springtime 2021

[摘要] An intense and long-lasting Saharan dust outbreak crossedthe 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 andmass contribution of both fine and coarse dust particles along theirtransport. Five Iberian lidar stations were monitoring the transport andevolution of the Saharan dust particles, i.e. El Arenosillo/Huelva,Granada, Torrejón/Madrid and Barcelona in Spain, and Évora inPortugal. The particular meteorological conditions determined the aerosolscenario along the overall dust event, differing in the first part of theevent (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 thesecond one (1–7 April). The use of the two-step POLIPHON algorithm showedthe relevance of using polarized lidar measurements for separating theaerosol properties of dust fine and coarse particles as an added value.Both the fine dust (Df) and coarse dust (Dc) components of the totalparticle backscatter coefficient (total dust, DD  =  Dc  +  Df) wereseparately derived. The dust plume was well-mixed with height and nosignificant differences were found in the vertical structure of both the Dcand Df particle backscatter coefficients. From the beginning of the dustoutbreak 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 atTorrejón/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 valueswere reported, being constant in its Df  /  DD ratio ( ∼   10  %)along the SW–NE dust pathway. In addition, the episode-mean centre-of-massheight increased with latitude overall, showing a high variability, beinggreater 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, theexpected ageing of the dust particles was hardly observed, by taking intoaccount the minor changes found in the contribution and properties of thecoarse and fine dust particles. This is on the basis that the IP isrelatively close to the Saharan dust sources and then, under certain dusttransport conditions, any potential ageing processes in the dust particlesremained unappreciated. The following must be highlighted: the different relativecontribution of the fine dust particles to the total dust found for theiroptical properties ( ∼   30  %) associated with the radiativeeffect of dust, with respect to that for the mass features ( ∼   10  %) linked to air quality issues, along the overall dust event bycrossing the IP.

[学科分类] 医学（综合）