Advanced measurements of aerosol formation and growth improve our understanding of the climate
The scientific community in Finland has a decades-long history of making novel measurements of atmospheric aerosols – the solid and liquid particles that can act as seeds for cloud droplets. Many of these measurements involve the formation of nano-scale aerosol from gases (particularly sulphuric acid vapour), via a process called nucleation. The longest set of continuous nucleation measurements have been carried out in Hyytiälä, Finland. However, because these observations are made in situ, there is a lot of uncertainty associated with the exact conditions under which they were made.
Researchers at the Finnish Meteorological Institute and the University of Helsinki have collaborated with leading scientists across Europe as part of the Marie Curie CLOUD-ITN project, which uses the CLOUD chamber facility at CERN to investigate the nucleation process at an unprecedented level of detail. The CLOUD chamber provides a unique study environment, which can better approximate the extremely clean and cold conditions of the free troposphere than any other facility.
For sulphuric acid and other vapours to form aerosols, they first need to stick together as molecular clusters. Kürten et al. (2015) uses two sophisticated instruments – the Chemical Ionization Mass Spectrometer (CIMS) and the Chemical Ionization–Atmospheric Pressure interface Time-Of-Flight (CI-APi-TOF) mass spectrometer – to study the formation of the sulphuric acid dimer, a cluster of just two molecules. For particles this small, there is a constant competition between molecules and clusters colliding and sticking together, and molecules evaporating from clusters. The paper provides estimates of some thermodynamic properties which can regulate this process, and shows how ammonia molecules can augment the formation of sulphuric acid dimers under some conditions.
In areas with high concentrations of organic vapours and amines, these vapours can increase nucleation rates. In an additional layer of complexity, the CIMS measures lower concentrations of sulphuric acid monomers (single molecules) in the presence of dimethyl amine (DMA). Previous studies suggested that the monomer concentration had remained constant, but the detection efficiency of the CIMS was decreased in the presence of DMA. Rondo et al. (2016) shows that the total sulphuric acid concentration available remains the same; however, much of it is trapped in molecular clusters, which can still contribute to particle nucleation and growth but are not measured by the CIMS. DMA has also been found to increase nucleation rates massively compared to a system with just sulphuric acid and water, or even with added ammonia, meaning that field measurements of nucleation will need to take local concentrations of DMA and other vapours into account when measuring sulphuric acid directly with a CIMS.
When particles have nucleated, they still need to grow efficiently to affect the climate. Smaller particles are much more likely to be lost to collisions with larger particles or other surfaces. In many nucleation models, only the effects of sulphuric acid on particle growth are accounted for. By using the advanced measurement techniques available in the CLOUD chamber, Lehtipalo et al. (2016) showed that both atmospheric ions and small acid-base clusters can contribute strongly to these growth rates, making it more likely that nucleated particles can reach atmospherically relevant sizes.
More information:
Researcher: Eimear Dunne, eimear.dunne@fmi.fi
Kürten, A., Münch, S., Rondo, L., Bianchi, F., Duplissy, J., Jokinen, T., Junninen, H., Sarnela, N., Schobesberger, S., Simon, M., Sipilä, M., Almeida, J., Amorim, A., Dommen, J., Donahue, N. M., Dunne, E. M., Flagan, R. C., Franchin, A., Kirkby, J., Kupc, A., Makhmutov, V., Petäjä, T., Praplan, A. P., Riccobono, F., Steiner, G., Tomé, A., Tsagkogeorgas, G., Wagner, P. E., Wimmer, D., Baltensperger, U., Kulmala, M., Worsnop, D. R., and Curtius, J.: Thermodynamics of the formation of sulfuric acid dimers in the binary (H2SO4–H2O) and ternary (H2SO4–H2O–NH3) system, Atmos. Chem. Phys., 15, 10701-10721, doi:10.5194/acp-15-10701-2015, 2015.
http://www.atmos-chem-phys.net/15/10701/2015/
Rondo, L., Ehrhart, S., Kürten, A., Adamov, A., Bianchi, F., Breitenlechner, M., Duplissy, J., Franchin, A.,Dunne, E.M., Hakala, J., Hansel, A., Keskinen, H., Kim, J., Jokinen, T., Lehtipalo, K., Leiminger, M., Praplan, A., Riccobono, F., Rissanen, M.P., Sarnela, N., Schobesberger, S., Simon, M, Smith, J.N., Tomé, A., Tröstl, J., Tsagkogeorgas, G., Vaattovaara, P., Wagner, P.E., Williamson, C., Kirkby, J., and Curtius, J., Effect of dimethylamine on the gas phase sulfuric acid concentration measured by Chemical Ionization Mass Spectrometry, J. Geophys. Res. Atmos., doi:10.1002/2015JD023868.
http://onlinelibrary.wiley.com/doi/10.1002/2015JD023868/full
Katrianne Lehtipalo, Linda Rondo, Siegfried Schobesberger, Tuija Jokinen, Nina Sarnela, Jenni Kontkanen, Sebastian Ehrhart, Alessandro Franchin, Tuomo Nieminen, Francesco Riccobono, Mikko Sipilä, Andreas Kürten, Taina Yli-Juuti, Jonathan Duplissy, Alexey Adamov, João Almeida, Antonio Amorim, Federico Bianchi, Martin Breitenlechner, Josef Dommen, Andrew J. Downard, Eimear M. Dunne, Richard C. Flagan, Roberto Guida, Jani Hakala, Armin Hansel, Werner Jud, Juha Kangasluoma, Veli-Matti Kerminen, Helmi Keskinen, Jaeseok Kim, Agnieszka Kupc, Oona Kupiainen-Määttä, Ari Laaksonen, Michael J. Lawler, Markus Leiminger, Serge Mathot, Tinja Olenius, Ismael K. Ortega, Antti Onnela, Tuukka Petäjä, Arnaud Praplan, Matti P. Rissanen, Taina Ruuskanen, Filipe D. Santos, Simon Schallhart, Ralf Schnitzhofer, Mario Simon, James N. Smith, Jasmin Tröstl, Georgios Tsagkogeorgas, António Tomé, Petri Vaattovaara, Hanna Vehkamäki, Aron E. Vrtala, Paul E.Wagner, Christina Williamson, Daniela Wimmer, Paul M. Winkler, Annele Virtanen, Neil M. Donahue, Kenneth S. Carslaw, Urs Baltensperger, Jasper Kirkby, Ilona Riipinen, Joachim Curtius, Douglas R. Worsnop, The effect of acid–base clustering and ions on the growth of atmospheric nano-particles, Nature Communications, doi:10.1038/ncomms11594.*
http://www.nature.com/ncomms/2016/160520/ncomms11594/full/ncomms11594.html