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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 27 Jun 2019

Research article | 27 Jun 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Impact of Isolated Atmospheric Aging processes on the Cloud Condensation Nuclei-activation of Soot Particles

Franz Friebel1, Prem Lobo1,2,a, David Neubauer1, Ulrike Lohmann1, Saskia Drossaart van Dusseldorp1, Evelyn Mühlhofer1, and Amewu A. Mensah1 Franz Friebel et al.
  • 1Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, 8092, Switzerland
  • 2Center of Excellence for Aerospace Particulate Emissions Reduction Research, Missouri University of Science and Technology, Rolla, Missouri 65401, USA
  • anow at: Metrology Research Centre, National Research Council Canada, Ottawa, Ontario K1A 0R6, Canada

Abstract. The largest contributors to the uncertainty in assessing the anthropogenic contribution in radiative forcing are the direct and indirect effects of aerosol particles on the Earth's radiative budget. Soot particles are of special interest since their properties can change significantly due to aging processes once they are emitted to the atmosphere. Probably the largest obstacle for the investigation of these processes in the laboratory is the long atmospheric lifetime of one week, demanding tailored experiments that cover this time span. This work presents results on the ability of two types of soot to act as cloud condensation nuclei (CCN) after exposure to atmospherically relevant levels of ozone and humidity. Aging times of up to 12 h were achieved by successful application of the continuous-flow stirred tank reactor (CSTR) concept while allowing for size-selection of particles prior to the aging step. 100 nm particles rich in organic carbon (OC) that were initially CCN-inactive showed significant CCN-activity at supersaturations (SS) down to 0.3 % after 10 h of exposure to 200 ppb of ozone. While this process was not affected by different levels of relative humidity in the range 5–75 %, a high sensitivity towards the ambient/reaction temperature was observed. Soot particles with a lower OC-content demanded an approximately four-fold longer aging duration to show CCN-activity for the same SS. Prior to the slow change in the CCN-activity, a rapid increase in the particle diameter was detected which occurred within several minutes. This study highlights the applicability of the CSTR-approach for the simulation of atmospheric aging processes, as aging durations beyond 12 h can be achieved in comparably small aerosol chamber volumes (< 3 m3). Implementation of our measurement results on the CCN-activity of soot particles retrieved from measurements at atmospherically relevant conditions into a global aerosol-climate model showed a statistically significant increase in the regional and global CCN burden and cloud droplet number concentration (CDNC).

Franz Friebel et al.
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Franz Friebel et al.
Franz Friebel et al.
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Publications Copernicus
Short summary
We investigated the change in cloud droplet activity of size-selected soot particles after being exposed to atmospheric levels of ozone over the course of 12 hours. For this, we operated a 3 m3 aerosol chamber in continuous-flow mode. The results were fed into a climate model (ECHAM-HAM). It was found that the oxidation of soot particles with ozone is a significant source of cloud condensation nuclei in the atmosphere.
We investigated the change in cloud droplet activity of size-selected soot particles after being...