Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 16, 7295-7315, 2016
https://doi.org/10.5194/acp-16-7295-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
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 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.

Citation: Rosati, B., Gysel, M., Rubach, F., Mentel, T. F., Goger, B., Poulain, L., Schlag, P., Miettinen, P., Pajunoja, A., Virtanen, A., Klein Baltink, H., Henzing, J. S. B., Größ, J., Gobbi, G. P., Wiedensohler, A., Kiendler-Scharr, A., Decesari, S., Facchini, M. C., Weingartner, E., and Baltensperger, U.: Vertical profiling of aerosol hygroscopic properties in the planetary boundary layer during the PEGASOS campaigns, Atmos. Chem. Phys., 16, 7295-7315, https://doi.org/10.5194/acp-16-7295-2016, 2016.
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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.
This study presents PEGASOS project data from field campaigns in the Po Valley, Italy and the...
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