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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 13, issue 15 | Copyright
Atmos. Chem. Phys., 13, 7645-7663, 2013
https://doi.org/10.5194/acp-13-7645-2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 08 Aug 2013

Research article | 08 Aug 2013

Formation and growth of nucleated particles into cloud condensation nuclei: model–measurement comparison

D. M. Westervelt1, J. R. Pierce2, I. Riipinen1,3, W. Trivitayanurak4, A. Hamed5,6, M. Kulmala7, A. Laaksonen7,8, S. Decesari9, and P. J. Adams1 D. M. Westervelt et al.
  • 1Center for Atmospheric Particle Studies (CAPS), Carnegie Mellon University, Pittsburgh, PA, USA
  • 2Department Atmospheric Science, Colorado State University, Fort Collins, CO, USA
  • 3Department of Applied Environmental Science, University of Stockholm, Stockholm, Sweden
  • 4Department of Highways, Bangkok, Thailand
  • 5Department of Applied Physics, University of Eastern Finland, Kuopio, Finland
  • 6Leibniz Institute for Tropospheric Research, Department of Physics, Leipzig, Germany
  • 7Department of Physics, University of Helsinki, Helsinki, Finland
  • 8Finnish Meteorological Institute, Helsinki, Finland
  • 9Institute of Atmospheric Sciences and Climate, Italian National Research Council (ISAC-CNR), Bologna, Italy

Abstract. Aerosol nucleation occurs frequently in the atmosphere and is an important source of particle number. Observations suggest that nucleated particles are capable of growing to sufficiently large sizes that they act as cloud condensation nuclei (CCN), but some global models have reported that CCN concentrations are only modestly sensitive to large changes in nucleation rates. Here we present a novel approach for using long-term size distribution observations to evaluate a global aerosol model's ability to predict formation rates of CCN from nucleation and growth events. We derive from observations at five locations nucleation-relevant metrics such as nucleation rate of particles at diameter of 3 nm (J3), diameter growth rate (GR), particle survival probability (SP), condensation and coagulation sinks, and CCN formation rate (J100). These quantities are also derived for a global microphysical model, GEOS-Chem-TOMAS, and compared to the observations on a daily basis. Using GEOS-Chem-TOMAS, we simulate nucleation events predicted by ternary (with a 10−5 tuning factor) or activation nucleation over one year and find that the model slightly understates the observed annual-average CCN formation mostly due to bias in the nucleation rate predictions, but by no more than 50% in the ternary simulations. At the two locations expected to be most impacted by large-scale regional nucleation, Hyytiälä and San Pietro Capofiume, predicted annual-average CCN formation rates are within 34 and 2% of the observations, respectively. Model-predicted annual-average growth rates are within 25% across all sites but also show a slight tendency to underestimate the observations, at least in the ternary nucleation simulations. On days that the growing nucleation mode reaches 100 nm, median single-day survival probabilities to 100 nm for the model and measurements range from less than 1–6% across the five locations we considered; however, this does not include particles that may eventually grow to 100 nm after the first day. This detailed exploration of new particle formation and growth dynamics adds support to the use of global models as tools for assessing the contribution of microphysical processes such as nucleation to the total number and CCN budget.

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