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Preprints
https://doi.org/10.5194/acp-2020-99
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-99
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 10 Feb 2020

Submitted as: research article | 10 Feb 2020

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This preprint is currently under review for the journal ACP.

The Aarhus Chamber Campaign on Highly Oxidized Multifunctional Organic Molecules and Aerosols (ACCHA): Particle Formation and Detailed Chemical Composition at Different Temperatures

Kasper Kristensen1, Louise N. Jensen2, Lauriane L. J. Quéléver3, Sigurd Christiansen2, Bernadette Rosati2,4, Jonas Elm2, Ricky Teiwes4, Henrik B. Pedersen4, Marianne Glasius2, Mikael Ehn3, and Merete Bilde2 Kasper Kristensen et al.
  • 1Department of Engineering, Aarhus University, 8000 Aarhus C, Denmark
  • 2Department of Chemistry and iClimate, Aarhus University, 8000 Aarhus C, Denmark
  • 3Institute for Atmospheric and Earth System Research – INAR/Physics, P.O. Box 64, 00014, University of Helsinki, Finland
  • 4Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark

Abstract. Little is known about the effects of low temperatures on the formation of SOA from α-pinene. In the current work, ozone-initiated oxidation of α-pinene at initial concentrations of 10 and 50 ppb, respectively, is performed at temperatures of 20, 0 and −15 °C in the Aarhus University Research on Aerosol (AURA) smog chamber during the Aarhus Chamber Campaign on highly oxidized multifunctional organic molecules and Aerosol (ACCHA). Here, we show how temperature influences the formation and chemical composition of α-pinene-derived SOA with a specific focus on the formation of organic acids and dimer esters. With respect to particle formation, results show significant increase in both particle formation rates, particle number concentrations and particle mass concentrations at lower temperatures. In particular, the number concentrations of sub-10 nm particles were significantly enhanced at the lower 0 and -15 °C temperatures. Temperatures also affect chemical composition of the formed SOA. Here, detailed off-line chemical analyses show organic acids contributing from 15 to 30 % by mass, with highest contributions observed at the lower temperatures indicative of enhanced condensation of these semi-volatile species. In comparison, 30 identified dimer esters contribute between 4–11 % to SOA mass. No significant differences in the chemical composition (i.e. organic acids and dimer esters) of the α-pinene-derived SOA particles are observed between experiments performed at 10 and 50 ppb initial α-pinene concentrations, thus suggesting a higher influence of reaction temperature compared to that of α-pinene loading on the SOA chemical composition. Interestingly, the effect of temperature on the formation of dimer esters differs between the individual species. The formation of less oxidized (oxygen-to-carbon ratio (O:C) < 0.4) dimer esters is shown to increase at lower temperatures while the formation of the more oxidized (O:C > 0.4) species is suppressed, consequently resulting in temperature-modulated composition of the α-pinene derived SOA. Temperature ramping experiments exposing α-pinene-derived SOA to changing temperatures (heating and cooling) reveal that the chemical composition of the SOA with respect to dimer esters is governed almost solely by the temperature during the initial oxidization and insusceptible to subsequent changes in temperature. Similarly, the resulting SOA mass concentrations were found to be more influenced by the initial α-pinene oxidation temperatures, thus suggesting that the formation conditions to a large extent govern the type of SOA formed, rather than the conditions to which the SOA is later exposed.

For the first time, we discuss the relation between the identified dimer ester and the highly oxidized multifunctional organic molecules (HOMs) measured by Chemical Ionization Atmospheric Pressure interface Time-of-Flight mass spectrometer (CI-APi-TOF) during ACCHA experiments. We propose that, although very different in chemical structures and O:C-ratios, dimer esters and HOMs may be linked through the mechanism of RO2 autoxidation, and that dimer esters and HOMs merely represent two different fates of the RO2 radicals.

Kasper Kristensen et al.

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Latest update: 27 May 2020
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Short summary
Atmospheric particles are important in relation to human health and the global climate. As the global temperature changes, so may the atmospheric chemistry controlling the formation of particles formed from the reactions of natural emitted volatile organic compounds (VOCs). In the current work, we show how temperatures influence the formation and chemical composition of atmospheric particles from α-pinene; a biogenic VOC largely emitted in high-latitude environments such as the boreal forests.
Atmospheric particles are important in relation to human health and the global climate. As the...
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