Marina Ealo

Spatiotemporal evolution of a severe winter dust event in the western Mediterranean: Aerosol optical and physical properties

An outstanding Saharan dust event affected the Iberian Peninsula during winter 2016 (20 to 25 February). The impact of this event on ambient PM10 surface levels and its spatial and temporal evolution was investigated by means of data from 250 air quality stations across mainland Spain and the Balearic Islands. The event had a significant impact on surface PM10 levels, and on 22 February, 90% of the air quality monitoring sites registered PM10 concentrations above the EU daily limit value of 50 µg/m3. The study of the attenuated backscattering vertical profiles associated with African dust evidenced a complex structure, with a thick aerosol layer that was at higher altitudes over the pre-Pyrenees compared to the coastal area of Barcelona but closer to the surface than typically observed at both sites. Optical and physical properties of dust particles were investigated at the continental background Global Atmosphere Watch mountain observatory of Montsec (MSA) in the pre-Pyrenees. Good agreement was found between in situ and passive remote sensing methodologies once the aloft dust layer reached the MSA station. Scattering Angstrom exponent values decreased to values close to zero (even below zero for surface in situ measurements) indicating the predominance of coarse particles. On the contrary, absorption Angstrom exponent values increased during the Saharan dust outbreak denoting an absorption enhancement at shorter wavelengths, characteristic of mineral dust particles. Furthermore, the performance of NMMB/BSC-Dust and BSC-DREAM8b models has been qualitatively evaluated for the dust spatial distribution across Spain and the vertical structure over MSA and Barcelona showing good agreement.

Vertical and horizontal distribution of regional new particle formation events in Madrid

The vertical profile of new particle formation (NPF) events was studied by comparing the aerosol size number distributions measured aloft and at surface level in a suburban environment in Madrid, Spain, using airborne instruments. The horizontal distribution and regional impact of the NPF events was investigated with data from three urban, urban background, and suburban stations in the Madrid metropolitan area. Intensive regional NPF episodes followed by particle growth were simultaneously recorded at three stations in and around Madrid during a field campaign in July 2016. The urban stations presented larger formation rates compared to the suburban station. Condensation and coagulation sinks followed a similar evolution at all stations, with higher values at urban stations. However, the total number concentration of particles larger than 2.5 nm was lower at the urban station and peaked around noon, when black carbon (BC) levels are at a minimum. The vertical soundings demonstrated that ultrafine particles (UFPs) are formed exclusively inside the mixed layer. As convection becomes more effective and the mixed layer grows, UFPs are detected at higher levels. The morning soundings revealed the presence of a residual layer in the upper levels in which aged particles (nucleated and grown on previous days) prevail. The particles in this layer also grow in size, with growth rates significantly smaller than those inside the mixed layer. Under conditions with strong enough convection, the soundings revealed homogeneous number size distributions and growth rates at all altitudes, which follow the same evolution at the other stations considered in this study. This indicates that UFPs are detected quasi-homogenously in an area spanning at least 17 km horizontally. The NPF events extend over the full vertical extension of the mixed layer, which can reach as high as 3000 m in the area, according to previous studies. On some days a marked decline in particle size (shrinkage) Published by Copernicus Publications on behalf of the European Geosciences Union. 16602 C. Carnerero et al.: Vertical and horizontal distribution of regional new particle formation events was observed in the afternoon, associated with a change in air masses. Additionally, a few nocturnal nucleation-mode bursts were observed at the urban stations, for which further research is needed to elucidate their origin.

Impact of Aerosol Microphysical Properties on Mass Scattering Cross Sections

We assessed the sensitivity of simulated mass scattering cross sections (\(\alpha ^{sca}_{\lambda }\) [m\(^{2}\)/g]) of three aerosol species to different particle microphysical properties and derived constraints on these microphysical properties for the north-western Mediterranean basin, by means of a comparison between code calculations and observations. In particular, we calculated \(\alpha ^{sca}_{\lambda }\) of mineral dust, organic carbon and sulfate at three wavelengths in the visible range with a T-matrix optical code, considering \({\pm }20\%\) perturbations on size distribution, refractive index and mass density, and oblate/prolate spheroids with two different axial ratios as shape perturbations. Then, we compared the simulation results with a set of observed \(\alpha ^{sca}_{\lambda }\) of mineral dust, aged organics and ammonium sulfate sources provided by the IDAEA-CSIC of Barcelona (Spain) and representative of the north-western Mediterranean basin.