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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 8
Atmos. Chem. Phys., 18, 5921-5930, 2018
https://doi.org/10.5194/acp-18-5921-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Atmos. Chem. Phys., 18, 5921-5930, 2018
https://doi.org/10.5194/acp-18-5921-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 27 Apr 2018

Research article | 27 Apr 2018

Experimental study of H2SO4 aerosol nucleation at high ionization levels

Maja Tomicic, Martin Bødker Enghoff, and Henrik Svensmark Maja Tomicic et al.
  • National Space Institute, Danish Technical University, Elektrovej 327, Kgs. Lyngby, Denmark

Abstract. One hundred and ten direct measurements of aerosol nucleation rate at high ionization levels were performed in an 8m3 reaction chamber. Neutral and ion-induced particle formation from sulfuric acid (H2SO4) was studied as a function of ionization and H2SO4 concentration. Other species that could have participated in the nucleation, such as NH3 or organic compounds, were not measured but assumed constant, and the concentration was estimated based on the parameterization by Gordon et al. (2017). Our parameter space is thus [H2SO4]  = 4×106 − 3×107cm−3, [NH3+ org]  =  2.2ppb, T = 295K, RH = 38%, and ion concentrations of 1700–19000cm−3. The ion concentrations, which correspond to levels caused by a nearby supernova, were achieved with gamma ray sources. Nucleation rates were directly measured with a particle size magnifier (PSM Airmodus A10) at a size close to critical cluster size (mobility diameter of  ∼ 1.4nm) and formation rates at a mobility diameter of  ∼ 4nm were measured with a CPC (TSI model 3775). The measurements show that nucleation increases by around an order of magnitude when the ionization increases from background to supernova levels under fixed gas conditions. The results expand the parameterization presented in Dunne et al. (2016) and Gordon et al. (2017) (for [NH3 + org]  =  2.2ppb and T = 295K) to lower sulfuric acid concentrations and higher ion concentrations. The results make it possible to expand the parameterization presented in Dunne et al. (2016) and Gordon et al. (2017) to higher ionization levels.

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A supernova within a distance of about 100 pc from the Earth would increase the cosmic ray flux and thereby the atmospheric ionization. We study the impact of high ion concentrations on aerosol nucleation through experiments. The measurements show that nucleation increases by up to an order of magnitude when the ionization increases from background to supernova levels under fixed concentrations of the nucleating gas. This suggests that a supernova could influence the atmospheric microphysics.
A supernova within a distance of about 100 pc from the Earth would increase the cosmic ray flux...
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