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Warming-induced increase in aerosol number concentration likely to moderate climate change


Atmospheric aerosol particles influence the climate system directly by scattering and absorbing solar radiation, and indirectly by acting as cloud condensation nuclei1,2,3,4. Apart from black carbon aerosol, aerosols cause a negative radiative forcing at the top of the atmosphere and substantially mitigate the warming caused by greenhouse gases1. In the future, tightening of controls on anthropogenic aerosol and precursor vapour emissions to achieve higher air quality may weaken this beneficial effect5,6,7. Natural aerosols, too, might affect future warming2,3,8,9. Here we analyse long-term observations of concentrations and compositions of aerosol particles and their biogenic precursor vapours in continental mid- and high-latitude environments. We use measurements of particle number size distribution together with boundary layer heights derived from reanalysis data to show that the boundary layer burden of cloud condensation nuclei increases exponentially with temperature. Our results confirm a negative feedback mechanism between the continental biosphere, aerosols and climate: aerosol cooling effects are strengthened by rising biogenic organic vapour emissions in response to warming, which in turn enhance condensation on particles and their growth to the size of cloud condensation nuclei. This natural growth mechanism produces roughly 50% of particles at the size of cloud condensation nuclei across Europe. We conclude that biosphere–atmosphere interactions are crucial for aerosol climate effects and can significantly influence the effects of anthropogenic aerosol emission controls, both on climate and air quality.

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Figure 1: Measurement locations and data periods.
Figure 2: The relationship between air temperature and the number concentration and burden of CCN-sized aerosol particles.
Figure 3: Concentration N100 as a function of gas phase monoterpene concentration ([MT]) and organic aerosol mass mOA (inset) at T>5 °C.
Figure 4: Schematic and estimated regional strengths of the proposed climate feedback mechanism.
Figure 5: Schematic summarizing the implications of the temperature dependence of CCN-sized particle burdens (B100).


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This work was funded by European Research Council (ATMNUCLE, 227463), Academy of Finland (Center of Excellence Program project 1118615; projects 11750, 127210, 132640 and 139656), European Commission sixth Framework program (EUCAARI, contract no 036833-2; EUSAAR, contract no 026140), European Commission seventh Framework program (ACTRIS, contract no 262254; PEGASOS, contract no 265148), Maj and Tor Nessling Foundation (projects 2010143, 2011200, 2012443 and 2013325) and the Otto A. Malm foundation. For providing data, we acknowledge the Physical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado (for the boundary layer height data acquired from their web site at, the Hungarian Meteorological Service, Gerald Spindler, Pasi P. Aalto and Harald Flentje. We thank Ville Vakkari for help in quality assurance of Botsalano data and students and staff of North-West University (Mafikeng Campus), RSA, for weekly maintenance. The various measurements were supported by the German Federal Ministry for the Environment (FE 370343200), Environment Canada, NSERC, CFCAS-CAFC, the National Science Foundation (#0544745 and supplement, and 1102309), the Swedish Research Council (projects 2007-3745, 2007-4619 and 2010-4683) and the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (Formas, project 2009-615).

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P.P. had the original idea; P.P. and A. Asmi made the data analysis; A. Asmi made the figures; M.K.K., T.H. and C.P-D. made the monoterpene concentration measurements and the data pre-analysis; M.Ä., H.J. and J.P.D.A. made the aerosol mass concentration measurements; A. Asmi, V-M.K., A.L. and P.R. made the calculations of the feedback strength; A. Arneth, W.B., A. Hamed, A. Hoffer, T.H., L.L., W.R.L., S.C.P., E.S., A.W. and T.P. provided the particle number size distribution and meteorological data; H.D.v.d.G. provided the anthropogenic emission inventory data; T.P., D.R.W. and M.K. supervised the analysis and writing; P.P., A. Asmi and V-M.K. wrote the paper; All authors contributed with their comments to the paper.

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Correspondence to Pauli Paasonen or Ari Asmi.

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The authors declare no competing financial interests.

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Paasonen, P., Asmi, A., Petäjä, T. et al. Warming-induced increase in aerosol number concentration likely to moderate climate change. Nature Geosci 6, 438–442 (2013).

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