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Preprints
https://doi.org/10.5194/acp-2020-55
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-55
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  27 Jan 2020

27 Jan 2020

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A revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Kinetic modelling of formation and evaporation of SOA from NO3 oxidation of pure and mixed monoterpenes

Thomas Berkemeier1,a, Masayuki Takeuchi2, Gamze Eris3, and Nga L. Ng1,3 Thomas Berkemeier et al.
  • 1School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, USA
  • 2School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA, USA
  • 3School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
  • anow at: Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz, Germany

Abstract. Organic aerosol constitutes a major fraction of the global aerosol burden and is predominantly formed as secondary organic aerosol (SOA). Environmental chambers have been used extensively to study aerosol formation and evolution under controlled conditions similar to the atmosphere, but quantitative prediction of the outcome of these experiments is generally not achieved, which signifies our lack in understanding of these results and limits their portability to large scale models. In general, kinetic models employing state-of-the-art explicit chemical mechanisms fail to describe the mass concentration and composition of SOA obtained from chamber experiments. Specifically, chemical reactions involving nitrate radical (NO3) oxidation of volatile organic compounds (VOCs) are a source of major uncertainty for assessing the chemical and physical properties of oxidation products. Here, we introduce a kinetic model that treats gas-phase chemistry, gas-particle partitioning, particle-phase oligomerization, and chamber wall loss and use it to describe the oxidation of the monoterpenes α-pinene and limonene with NO3. The model can reproduce aerosol mass and nitration degrees in experiments using either pure precursors or their mixtures and infers volatility distributions of products, branching ratios of reactive intermediates as well as particle-phase reaction rates. The gas-phase chemistry in the model is based on the Master Chemical Mechanism (MCM), but trades speciation of single compounds for the overall ability of quantitatively describing SOA formation by using a lumped chemical mechanism. The complex branching into a multitude of individual products in MCM is replaced in this model with product volatility distributions, detailed peroxy (RO2) and alkoxy (RO) radical chemistry and amended by a particle-phase oligomerization scheme. The kinetic parameters obtained in this study are constrained by a set of SOA formation and evaporation experiments conducted in the Georgia Tech Environmental Chamber (GTEC) facility. For both precursors, we present volatility distributions of nitrated and non-nitrated reaction products that are obtained by fitting the kinetic model systematically to the experimental data using a global optimization method, the Monte Carlo Genetic Algorithm (MCGA). The results presented here provide new mechanistic insight into the processes leading to formation and evaporation of SOA. Most notably, much of the non-linear behavior of precursor mixtures can be understood by RO2 fate and reversible oligomerization reactions in the particle phase, but some effects could be accredited to kinetic limitations of mass transport in the particle phase. The methodologies described in this work provide a basis for quantitative analysis of multi-source data from environmental chamber experiments with manageable computational effort.

Thomas Berkemeier et al.

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Thomas Berkemeier et al.

Thomas Berkemeier et al.

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Latest update: 28 Nov 2020
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Short summary
This manuscript presents how environmental chamber data of secondary organic aerosol (SOA) formation can be interpreted using kinetic modelling techniques. Utilizing pure and mixed precursor experiments, we show that SOA formation and evaporation can be understood by explicitly treating gas-phase chemistry, gas-particle partitioning and, notably, particle-phase oligomerization, but some of the non-linear, non-equilibrium effects must be accredited to diffusion limitations in the particle phase.
This manuscript presents how environmental chamber data of secondary organic aerosol (SOA)...
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