Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 4 2 2004 10.5194/acp-4-557-2004 http://www.atmos-chem-phys.net/4/557/2004/ http://www.atmos-chem-phys.net/4/557/2004/acp-4-557-2004.html http://www.atmos-chem-phys.net/4/557/2004/acp-4-557-2004.pdf 557 562 2004-03-30 A new feedback mechanism linking forests, aerosols, and climate M. Kulmala T. Suni K. E. J. Lehtinen M. Dal Maso M. Boy A. Reissell Ü. Rannik P. Aalto P. Keronen H. Hakola J. Bäck T. Hoffmann T. Vesala P. Hari University of Helsinki, Department of Physical Sciences, P.O. Box 64, FIN-00014, University of Helsinki, Finland Finnish Meteorological Institute, Sahaajankatu 20 E, FIN-00880 Helsinki, Finland University of Helsinki, Department of Chemistry, P.O. Box 55, FIN-00014 University of Helsinki, Finland University of Helsinki, Department of Forest Ecology, P.O. Box 27, FIN-00014, University of Helsinki, Finland Institute of Spectrochemistry and Applied Spectroscopy, Bunsen-Kirchhoffstr. 11, D-44139 Dortmund, Germany The possible connections between the carbon balance of ecosystems and aerosol-cloud-climate interactions play a significant role in climate change studies. Carbon dioxide is a greenhouse gas, whereas the net effect of atmospheric aerosols is to cool the climate. Here, we investigated the connection between forest-atmosphere carbon exchange and aerosol dynamics in the continental boundary layer by means of multiannual data sets of particle formation and growth rates, of CO₂ fluxes, and of monoterpene concentrations in a Scots pine forest in southern Finland. We suggest a new, interesting link and a potentially important feedback among forest ecosystem functioning, aerosols, and climate: Considering that globally increasing temperatures and CO₂ fertilization are likely to lead to increased photosynthesis and forest growth, an increase in forest biomass would increase emissions of non-methane biogenic volatile organic compounds and thereby enhance organic aerosol production. This feedback mechanism couples the climate effect of CO₂ with that of aerosols in a novel way.