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Published August 29, 2012 | Supplemental Material
Journal Article Open

Biogenic Potassium Salt Particles as Seeds for Secondary Organic Aerosol in the Amazon


The fine particles serving as cloud condensation nuclei in pristine Amazonian rainforest air consist mostly of secondary organic aerosol. Their origin is enigmatic, however, because new particle formation in the atmosphere is not observed. Here, we show that the growth of organic aerosol particles can be initiated by potassium-salt–rich particles emitted by biota in the rainforest. These particles act as seeds for the condensation of low- or semi-volatile organic compounds from the atmospheric gas phase or multiphase oxidation of isoprene and terpenes. Our findings suggest that the primary emission of biogenic salt particles directly influences the number concentration of cloud condensation nuclei and affects the microphysics of cloud formation and precipitation over the rainforest.

Additional Information

© 2012 American Association for the Advancement of Science. Received for publication 12 April 2012; accepted for publication 23 July 2012. This work has been supported by the Max Planck Society, the Max Planck Graduate Center, the Geocycles Cluster Mainz (Landesexzellenzcluster Rheinland-Pfalz), and the European Community (PEGASOS, FP7-265148). The Harvard Environmental Chamber was supported by the Office of Science, Office of Basic Energy Sciences (BES), U.S. Department of Energy (DOE), grant no. DE-FG02-08ER6452, and the U.S. NSF under grant no. 0925467. The Advanced Light Source is supported by the Director, Office of Science, BES, of the U.S. DOE under contract no. DE-AC02-05CH11231. We thank the Helmholtz-Zentrum Berlin for the allocation of synchrotron radiation beamtime at BESSY II. We thank the Instituto Nacional de Pesquisas da Amazônia (INPA), Manaus, and the ATTO team under the Brazilian coordinator, A. O. Manzi, for their collaboration and field support. We also thank G. R. Carmichael and the Center for Global and Regional Environmental Research at the University of Iowa for support in the Weather Research and Forecasting (WRF) model simulations. We gratefully acknowledge R. Ditz, I. Trebs, X. Chi, J. A. Huffman, J. Kesselmeier, J. Schöngart, M. Kuwata, T. Tyliszczak, J. Huth, G. Schütz, E. Goering, M. Bechtel, J.-D. Förster, and T. Behrendt for support and helpful discussions.

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