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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 16, issue 22
Atmos. Chem. Phys., 16, 14585–14598, 2016
https://doi.org/10.5194/acp-16-14585-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: The CERN CLOUD experiment (ACP/AMT inter-journal SI)

Atmos. Chem. Phys., 16, 14585–14598, 2016
https://doi.org/10.5194/acp-16-14585-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 23 Nov 2016

Research article | 23 Nov 2016

A Monte Carlo approach for determining cluster evaporation rates from concentration measurements

Oona Kupiainen-Määttä Oona Kupiainen-Määttä
  • Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland

Abstract. Evaporation rates of small negatively charged sulfuric acid–ammonia clusters are determined by combining detailed cluster formation simulations with cluster distributions measured in the CLOUD experiment at CERN. The analysis is performed by varying the evaporation rates with Markov chain Monte Carlo (MCMC), running cluster formation simulations with each new set of evaporation rates and comparing the obtained cluster distributions to the measurements. In a second set of simulations, the fragmentation of clusters in the mass spectrometer due to energetic collisions is studied by treating also the fragmentation probabilities as unknown parameters and varying them with MCMC. This second set of simulations results in a better fit to the experimental data, suggesting that a large fraction of the observed HSO4 and HSO4 ⋅ H2SO4 signals may result from fragmentation of larger clusters, most importantly the HSO4 ⋅ (H2SO4)2 trimer.

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The article introduces a new method for determining the evaporation rates of small molecular clusters based on cluster concentration measurements. Evaporation rates cannot be measured directly or computed very accurately from any classical or quantum theory, so the presented method will give new understanding about molecular clusters. In addition, it can give some information about what happens to clusters during the measurement process.
The article introduces a new method for determining the evaporation rates of small molecular...
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