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Preprints
https://doi.org/10.5194/acp-2020-837
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-837
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  25 Aug 2020

25 Aug 2020

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This preprint is currently under review for the journal ACP.

Aircraft vertical profiles during summertime regional and Saharan dust scenarios over the north-western Mediterranean Basin: aerosol optical and physical properties

Jesús Yus-Díez1,2, Marina Ealo1,2, Marco Pandolfi1, Noemí Perez1, Gloria Titos1,3, Griša Močnik4,5, Xavier Querol1, and Andrés Alastuey1 Jesús Yus-Díez et al.
  • 1Institute of Environmental Assessment and Water Research (IDAEA-CSIC), C/Jordi Girona 18-26, 08034, Barcelona, Spain
  • 2Departament de Física Aplicada - Meteorologia, Universitat de Barcelona, C/Martí i Franquès, 1., 08028, Barcelona, Spain
  • 3Andalusian Institute for Earth System Research (IISTA-CEAMA), University of Granada, Autonomous Government of Andalusia, Granada, Spain
  • 4Center for Atmospheric Research, University of Nova Gorica, Vipavska 11c, 5270 Ajdovščina, Slovenia
  • 5Department of Condensed Matter Physics, Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia

Abstract. Accurate measurements of the horizontal and vertical distribution of atmospheric aerosol particle optical properties are key for a better understanding of their impact on the climate. Here we present the results of a measurement campaign based on instrumented flights over NE Spain. We measured vertical profiles of size segregated atmospheric particulate matter (PM) mass concentrations and multi-wavelength scattering and absorption coefficients in the Western Mediterranean Basin (WMB). The campaign took place during typical summer conditions, characterized by the development of a vertical multi-layer structure, under both summer regional pollution episodes (REG) and Saharan dust events (SDE). REG patterns in the region form under high insolation and scarce precipitation in summer, favoring layering of highly-aged fine PM strata in the lower few km a.s.l. The REG scenario prevailed during the entire measurement campaign. Additionally, African dust outbreaks and plumes from North African wildfires influenced the study area. The vertical profiles of climate relevant intensive optical parameters such as single scattering albedo (SSA), asymmetry parameter (g), scattering, absorption and SSA Angstrom exponents (SAE, AAE, SSAAE), and PM mas scattering and absorption cross sections (MSC and MAE) were derived from the measurements. Moreover, we compared the aircraft measurements with those performed at two GAW/ACTRIS surface measurement stations located in NE Spain, namely: Montseny (MSY; regional background) and Montsec d'Ares (MSA; remote site).

Airborne in-situ measurements and ceilometer ground-based remote measurements identified aerosol air masses at altitude up to more than 3.5 km a.s.l. The vertical profiles of the optical properties markedly changed according to the prevailing atmospheric scenarios. During SDE the SAE was low along the profiles, reaching values < 1.0 in the dust layers. Correspondingly, SSAAE was negative and AAE reached values up to 2.0–2.5, as a consequence of the UV absorption increased by the presence of the coarse dust particles. During REG, the SAE increased > 2.0 and the asymmetry parameter g was rather low (0.5–0.6) due to the prevalence of fine PM which were characterized by an AAE close to 1.0 suggesting a fossil fuel combustion origin. During REG, some of the layers featured larger AAE (> 1.5), relatively low SSA at 525 nm (< 0.85) and high MSC (> 9 m2 g−1) and were associated to the influence of PM from wildfires. Overall, the SSA and MSC near the ground ranged around 0.85 and 3 m2 g−1, respectively and increased at higher altitudes, reaching values above 0.95 and up to 9 m2 g−1. The PM, MSC and MAE were on average larger during REG compared to SDE due to the larger scattering and absorption efficiency of fine PM compared with dust. The SSA and MSC had quite similar vertical profiles and often both increased with height indicating the progressive shift toward PM with larger scattering efficiency with altitude.

This study contributes to our understanding of regional aerosol vertical distribution and optical properties in the WMB and the results will be useful for improving future climate projections and remote sensing/satellite retrieval algorithms.

Jesús Yus-Díez et al.

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Jesús Yus-Díez et al.

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Short summary
Here we describe the vertical profiles of aerosol optical properties – both extensive (scattering and absorption) and intensive (e.g. albedo and asymmetry parameter), obtained coupling ground based measurements from two sites in NE Spain with airborne measurements performed with an aircraft. We analyze different aerosol layers along the vertical profile for a regional pollution episode and a Saharan dust intrusion. The results show a change with height depending on the different measured layers.
Here we describe the vertical profiles of aerosol optical properties – both extensive...
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