For many years, TROPOS has participated in national and international cloud field measurement campaigns, which are part of research projects for the investigation of aerosol-cloud interactions in liquid clouds. These are orographic clouds, tropical trade wind clouds, low and medium high arctic clouds and cold but liquid strato cumulus clouds. The objectives of these field experiments are:

  • Identification of the chemical and microphysical properties of aerosol particles that form/do not form cloud droplets in the real atmosphere (especially compared to particle activation in condensation nucleus counters)
  • Quantification of the phase partitioning of atmospheric aerosol substances in the liquid and interstitial phase
  • Determination of the effect of cloud processing on atmospheric aerosol particles (change of chemical composition and size)
  • Provision of input and validation parameters for cloud chemistry and microphysical models

The experimental in-situ cloud investigations are carried out both on the ground (i.e. mainly at mountain measurement stations) and aircraft-borne. Inside the cloud the droplets and the interstitial aerosol are collected separately using a counterflow virtual impactor (CVI) and an interstitial inlet. After drying of the droplets in the airborne state within the CVI, both the droplet residues and the interstitial particles are analyzed microphysically (number, size, morphology, electrical charge) and chemically (composition, mixing state), also in cooperation with working groups of other research institutes. Current research projects in which atmospheric clouds are studied are HCCT-2010, ACRIDICON and ACLOUD.


  • project logo

  • Measurement tower inside cloud at the measurement station Schmücke during HCCT-2010, Source: Stephan Mertes/TROPOS

HCCT-2010: Hill Cap Cloud Thuringia, Schmücke, Germany, ground-based (2010)

By measuring the microphysical and chemical properties of aerosol particles in front of the cloud, in the cloud (residual particles activated to droplets and non-activated interstitial particles) and after the cloud, it will be investigated which aerosol types contribute to cloud formation and which do not, and how activated aerosol particles are altered by cloud processing. In particular, the question is which supersaturations exist in the real cloud, which cannot be measured directly, but is an essential parameter for cloud process modeling. This will be determined by comparing the size-resolved activation measurements of aerosol particles in a cloud condensation chamber before cloud entry with those in the real cloud (via the size distribution of the residual and interstitial particles).

This project was supported by the Deutsche Forschungsgemeinschaft (German Research Foundation) with human resources (grant ME 3534/1-2).


  • ACRIDICON-CHUVA mission logo

  • The HALO research aircraft at Manaus airport with the HALO-CVI mounted in the centre at the top, source: Stephan Mertes/TROPOS

  • Deep convective cloud over the Amazon region during a mission flight, Source: Stephan Mertes/TROPOS

 ACRIDICON: Amazonia, Brazil, airborne (2014)

The scientific objectives of ACRIDICON include the investigation of cloud base activation, cloud processing and fast vertical transport of boundary layer aerosol particles in deep convective cloud systems in the tropics. It will also be investigated whether there is a difference between clean air masses and air masses polluted by biomass combustion. These measurements took place in autumn 2014 over the Brazilian Amazon region with the German research aircraft HALO. The HALO-CVI inlet was used to chemically and microphysically analyse the cloud residuals at different cloud heights.

This project was funded by the German Research Foundation (DFG Priority Program 1294, grant ME 3534/1-2)


  • ACLOUD mission logo

  • The Polar 6 research aircraft at the airport in Longyearbyen (Svalbard) with the CVI inlet (white), Source: Stephan Mertes/TROPOS

  • Low arctic cloud over the sea ice during ACLOUD, Source: Stephan Mertes/TROPOS

ACLOUD: Svalbard, Arctic, airborne (2017)

It is believed that low supercooled and mixed-phase clouds contribute significantly to increased Arctic warming. Therefore, a better understanding of the formation and stability of these Arctic clouds is needed. Closely related to cloud formation is the question on which Arctic aerosol particles these clouds form and what are the sources of these cloud condensation nuclei. The cloud forming particles can be produced, emitted or advected locally within the boundary layer and reach the cloud base. On the other hand, in the free troposphere, aerosol particles transported from far away can also be entrained into the cloud from above and contribute to drop formation. This scientific question will be investigated with the Polar 6 research aircraft of the Alfred Wegener Institute in the ACLOUD measurement campaign.

This project is funded by the German Research Foundation (DFG-Collaborative Research Center/Transregio 172, project B03)

Literature on HCCT-2010:

Schneider, J., S. Mertes, D. van Pinxteren, H. Herrmann and S. Borrmann (2017), Uptake of nitric acid, ammonia, and organics in orographic clouds: Mass spectrometric analyses of droplet residual and interstitial aerosol particles, Atmos. Chem. Phys.17: 1571-1593, DOI: doi:10.5194/acp-17-1571-2017

Roth, A., J. Schneider, T. Klimach, S. Mertes, D. van Pinxteren, H. Herrmann and S. Borrmann (2016), Aerosol properties, source identification, and cloud processing in orographic clouds measured by single particle mass spectrometry on a Central European mountain site during HCCT-2010, Atmos. Chem. Phys.16(2): 505-524, DOI: doi:10.5194/acp-16-505-2016

van Pinxteren, D., K. W. Fomba, S. Mertes, K. Müller, G. Spindler, J. Schneider, T. Lee, J. L. Collett and H. Herrmann (2016), Cloud water composition during HCCT-2010: Scavenging efficiencies, solute concentrations, and droplet size dependence of inorganic ions and dissolved organic carbon, Atmos. Chem. Phys.16: 3185–3205, DOI: doi:10.5194/acp-16-3185-2016

Whalley, L. K., D. Stone, I. J. George, S. Mertes, D. van Pinxteren, A. Tilgner, H. Herrmann, M. J. Evans and D. E. Heard (2015), The influence of clouds on radical concentrations: Observations and modelling studies of HOx during the Hill Cap Cloud Thuringia (HCCT) campaign in 2010, Atmos. Chem. Phys.15: 3289-3301, DOI: doi:10.5194/acp-15-3289-2015

Harris, E., B. Sinha, D. van Pinxteren, J. Schneider, L. Poulain, J. Collett, B. D´Anna, B. Fahlbusch, S. Foley, K. W. Fomba, C. George, T. Gnauk, S. Henning, T. Lee, S. Mertes, A. Roth, F. Stratmann, S. Borrmann, P. Hoppe and H. Herrmann (2014), In-cloud sulfate addition to single particles resolved with sulfur isotope analysis during HCCT-2010, Atmos. Chem. Phys.14: 4219-4235, DOI: doi:10.5194/acp-14-4219-2014

Henning, S., K. Dieckmann, K. Ignatius, M. Schäfer, P. Zedler, E. Harris, B. Sinha, D. van Pinxteren, S. Mertes, W. Birmili, M. Merkel, Z. Wu, A. Wiedensohler, H. Wex, H. Herrmann and F. Stratmann (2014), Influence of cloud processing on CCN activation behavior in the Thuringian Forest, Germany during HCCT-2010, Atmos. Chem. Phys.14: 7859-7868, DOI: doi:10.5194/acp-14-7859-2014

Tilgner, A., L. Schöne, P. Bräuer, D. van Pinxteren, E. Hoffmann, G. Spindler, S. A. Styler, S. Mertes, W. Birmili, R. Otto, M. Merkel, K. Weinhold, A. Wiedensohler, H. Deneke, R. Schrödner, R. Wolke, J. Schneider, W. Haunold, A. Engel, A. Wéber and H. Herrmann (2014), Comprehensive assessment of meteorological conditions and airflow connectivity during HCCT-2010, Atmos. Chem. Phys.14(Special Issue: HCCT-2010: A complex ground-based experiment on aerosol-cloud interaction): 9105-9128, DOI: doi:10.5194/acp-14-9105-2014

Harris, E., B. Sinha, D. van Pinxteren, A. Tilgner, W. Fomba, J. Schneider, A. Roth, T. Gnauk, B. Fahlbusch, S. Mertes, T. Lee, J. Collett, S. Foley, S. Borrmann, P. Hoppe and H. Herrmann (2013), Enhanced role of transition metal ion catalysis during in-cloud oxidation of SO2, Science340(6133): 727-730, DOI: doi:10.1126/science.1230911

Spiegel, J. K., F. Aemisegger, M. Scholl, F. G. Wienhold, J. L. Collett Jr., T. Lee, D. van Pinxteren, S. Mertes, A. Tilgner, H. Herrmann, R. A. Werner, N. Buchmann and W. Eugster (2012), Temporal evolution of stable water isotopologues in cloud droplets in a hill cap cloud in central Europe (HCCT-2010), Atmos. Chem. Phys.12(23): 11679-11694, DOI: doi:10.5194/acp-12-11679-2012

Spiegel, J. K., F. Aemisegger, M. Scholl, F. G. Wienhold, J. L. Collett Jr., T. Lee, D. van Pinxteren, S. Mertes, A. Tilgner, H. Herrmann, R. A. Werner, N. Buchmann and W. Eugster (2012), Stable water isotopologue ratios in fog and cloud droplets of liquid clouds are not size-dependent, Atmos. Chem. Phys.12(23): 9855-9863, DOI: doi:10.5194/acp-12-9855-2012

Literature on ACRIDICON:

Andreae, M. O., A. Afchine, R. Albrecht, B. A. Holanda, P. Artaxo, H. M. J. Barbosa, S. Bormann, M. A. Cecchini, A. Costa, M. Dollner, D. Fütterer, E. Järvinen, T. Jurkat, T. Klimach, T. Konemann, C. Knote, M. Krämer, T. Krisna, L. A. T. Machado, S. Mertes, A. Minikin, C. Pöhlker, M. L. Pöhlker, U. Pöschl, D. Rosenfeld, D. Sauer, H. Schlager, M. Schnaiter, J. Schneider, C. Schulz, A. Spanu, V. B. Sperling, C. Voigt, A. Walser, J. Wang, B. Weinzierl, M. Wendisch and H. Ziereis (2018), Aerosol characteristics and particle production in the upper troposphere over the Amazon Basin, Atmos. Chem. Phys.18(2): 921-961, DOI: doi:10.5194/acp-18-921-2018

Schulz, C., J. Schneider, B. A. Holanda, O. Appel, A. Costa, S. S. de Sá, V. Dreiling, D. Fütterer, T. Jurkat-Witschas, T. Klimach, C. Knote, M. Krämer, S. T. Martin, S. Mertes, M. L. Pöhlker, D. Sauer, C. Voigt, A. Walser, B. Weinzierl, H. Ziereis, M. Zöger, M. O. Andreae, P. Artaxo, L. A. T. Machado, U. Pöschl, M. Wendisch and S. Borrmann (2018), Aircraft-based observations of isoprene-epoxydiol-derived secondary organic aerosol (IEPOX-SOA) in the tropical upper troposphere over the Amazon region, Atmos. Chem. Phys.18(20): 14979-15001, DOI: doi:10.5194/acp-18-14979-2018

Wendisch, M., U. Pöschl, M. O. Andreae, L. A. T. Machado, R. Albrecht, H. Schlager, D. Rosenfeld, S. T. Martin, A. Abdelmonem, A. Afchine, A. Araùjo, P. Artaxo, H. Aufmhoff, H. M. J. Barbosa, S. Borrmann, R. Braga, B. Buchholz, M. A. Cecchini, A. Costa, J. Curtius, M. Dollner, M. Dorf, V. Dreiling, V. Ebert, A. Ehrlich, F. Ewald, G. Fisch, A. Fix, F. Frank, D. Fütterer, C. Heckl, F. Heidelberg, T. Hüneke, E. Jäkel, E. Järvinen, T. Jurkat, S. Kanter, U. Kästner, M. Kenntner, J. Kesselmeier, T. Klimach, M. Knecht, R. Kohl, T. Kölling, M. Krämer, M. Krüger, T. C. Krisna, J. V. Lavric, K. Longo, C. Mahnke, A. O. Manzi, B. Mayer, S. Mertes, A. Minikin, S. Molleker, S. Münch, B. Nilius, K. Pfeilsticker, C. Pöhlker, A. Roiger, D. Rose, D. Rosenow, D. Sauer, M. Schnaiter, J. Schneider, C. Schulz, R. A. F. de Souza, A. Spanu, P. Stock, D. Vila, C. Voigt, A. Walser, D. Walter, R. Weigel, B. Weinzierl, F. Werner, M. A. Yamasoe, H. Ziereis, T. Zinner and M. Zöger (2016), Introduction of the ACRIDICON–CHUVA campaign studying tropical deep convective clouds and precipitation over Amazonia using the new German research aircraft HALO, Bull. Amer. Meteor. Soc.97(10): 1885-1908, DOI: doi:10.1175/BAMS-D-14-00255.1

Literature on ACLOUD:

Wendisch, M., A. Macke, A. Ehrlich, C. Lüpkes, M. Mech, D. Chechin, K. Dethloff, C. Barrientos, H. Bozem, M. Brückner, H.-C. Clemen, S. Crewell, T. Donth, R. Dupuy, K. Ebell, U. Egerer, R. Engelmann, C. Engler, O. Eppers, M. Gehrmann, X. Gong, M. Gottschalk, C. Gourbeyre, H. Griesche, J. Hartmann, M. Hartmann, B. Heinold, A. Herber, H. Herrmann, G. Heygster, P. Hoor, S. Jafariserajehlou, E. Jäkel, E. Järvinen, O. Jourdan, U. Kästner, S. Kecorius, E. M. Knudsen, F. Köllner, J. Kretzschmar, L. Lelli, D. Leroy, M. Maturilli, L. Mei, S. Mertes, G. Mioche, R. Neuber, M. Nicolaus, T. Nomokonova, J. Notholt, M. Palm, M. van Pinxteren, J. Quaas, P. Richter, E. Ruiz-Donoso, M. Schäfer, K. Schmieder, M. Schnaiter, J. Schneider, A. Schwarzenböck, P. Seifert, M. D. Shupe, H. Siebert, G. Spreen, J. Stapf, F. Stratmann, T. Vogl, A. Welti, H. Wex, A. Wiedensohler, M. Zanatta and S. Zeppenfeld (2018), The Arctic cloud puzzle: Using ACLOUD/PASCAL multi-platform observations to unravel the role of clouds and aerosol particles in Arctic amplification, Bull. Amer. Meteor. Soc.: submitted