Articles | Volume 16, issue 11
Atmos. Chem. Phys., 16, 7295–7315, 2016

Special issue: BACCHUS – Impact of Biogenic versus Anthropogenic emissions...

Special issue: The Pan European Gas-Aerosols Climate Interaction Study...

Atmos. Chem. Phys., 16, 7295–7315, 2016

Research article 10 Jun 2016

Research article | 10 Jun 2016

Vertical profiling of aerosol hygroscopic properties in the planetary boundary layer during the PEGASOS campaigns

Bernadette Rosati1,a, Martin Gysel1, Florian Rubach2,3,b, Thomas F. Mentel2, Brigitta Goger1,c, Laurent Poulain3, Patrick Schlag2, Pasi Miettinen4, Aki Pajunoja4, Annele Virtanen4, Henk Klein Baltink5, J. S. Bas Henzing6, Johannes Größ3, Gian Paolo Gobbi7, Alfred Wiedensohler3, Astrid Kiendler-Scharr2, Stefano Decesari8, Maria Cristina Facchini8, Ernest Weingartner1,d, and Urs Baltensperger1 Bernadette Rosati et al.
  • 1Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland
  • 2Institute for Energy and Climate Research (IEK-8), Forschungszentrum Jülich, 52428 Jülich, Germany
  • 3Leibniz Institute for Tropospheric Research, 04318 Leipzig, Germany
  • 4Department of Applied Physics, University of Eastern Finland, 1627 Kuopio, Finland
  • 5Royal Netherlands Meteorological Institute (KNMI), 3730 De Bilt, the Netherlands
  • 6Netherlands Organization for Applied Scientific Research (TNO), 80015 Utrecht, the Netherlands
  • 7Institute of Atmospheric Sciences and Climate (ISAC-CNR), National Research Council, 00133 Rome, Italy
  • 8Institute of Atmospheric Sciences and Climate (ISAC-CNR), National Research Council, 40129 Bologna, Italy
  • anow at: Institute for Aerosol Physics and Environmental Physics, University of Vienna, 1090 Vienna, Austria
  • bnow at: Max Planck Institute for Chemistry, 55128 Mainz, Germany
  • cnow at: Institute of Meteorology and Geophysics, University of Innsbruck, 6020 Innsbruck, Austria
  • dnow at: Institute for Aerosol and Sensor Technology, University of Applied Science Northwestern Switzerland, 5210 Windisch, Switzerland

Abstract. Vertical profiles of the aerosol particles hygroscopic properties, their mixing state as well as chemical composition were measured above northern Italy and the Netherlands. An aerosol mass spectrometer (AMS; for chemical composition) and a white-light humidified optical particle spectrometer (WHOPS; for hygroscopic growth) were deployed on a Zeppelin NT airship within the PEGASOS project. This allowed one to investigate the development of the different layers within the planetary boundary layer (PBL), providing a unique in situ data set for airborne aerosol particles properties in the first kilometre of the atmosphere. Profiles measured during the morning hours on 20 June 2012 in the Po Valley, Italy, showed an increased nitrate fraction at  ∼  100 m above ground level (a.g.l.) coupled with enhanced hygroscopic growth compared to  ∼  700 m a. g. l. This result was derived from both measurements of the aerosol composition and direct measurements of the hygroscopicity, yielding hygroscopicity parameters (κ) of 0.34  ±  0.12 and 0.19  ±  0.07 for 500 nm particles, at  ∼  100 and  ∼  700 m a. g. l., respectively. The difference is attributed to the structure of the PBL at this time of day which featured several independent sub-layers with different types of aerosols. Later in the day the vertical structures disappeared due to the mixing of the layers and similar aerosol particle properties were found at all probed altitudes (mean κ ≈ 0.18  ±  0.07). The aerosol properties observed at the lowest flight level (100 m a. g. l.) were consistent with parallel measurements at a ground site, both in the morning and afternoon. Overall, the aerosol particles were found to be externally mixed, with a prevailing hygroscopic fraction. The flights near Cabauw in the Netherlands in the fully mixed PBL did not feature altitude-dependent characteristics. Particles were also externally mixed and had an even larger hygroscopic fraction compared to the results in Italy. The mean κ from direct measurements was 0.28 ±  0.10, thus considerably higher than κ values measured in Italy in the fully mixed PBL.

Short summary
This study presents PEGASOS project data from field campaigns in the Po Valley, Italy and the Netherlands. Vertical profiles of aerosol hygroscopicity and chemical composition were investigated with airborne measurements on board a Zeppelin NT airship. A special focus was on the evolution of different mixing layers within the PBL as a function of daytime. A closure study showed that variations in aerosol hygroscopicity can well be explained by the variations in chemical composition.
Final-revised paper