Preprints
https://doi.org/10.5194/acp-2020-100
https://doi.org/10.5194/acp-2020-100

  26 Feb 2020

26 Feb 2020

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

Temperature and VOC concentration as controlling factors for chemical composition of alpha-pinene derived secondary organic aerosol

Louise N. Jensen1, Manjula R. Canagaratna2, Kasper Kristensen3, Lauriane L. J. Quéléver4, Bernadette Rosati1,5, Ricky Teiwes5, Marianne Glasius1, Henrik B. Pedersen5, Mikael Ehn4, and Merete Bilde1 Louise N. Jensen et al.
  • 1Department of Chemistry, Aarhus University, 8000 Aarhus C, Denmark
  • 2Aerodyne Research, Inc., Billerica, MA, USA
  • 3Department of Engineering, Aarhus University, 8000 Aarhus C, Denmark
  • 4Institute for Atmospheric and Earth System Research –INAR / Physics, P.O. Box 64, 00014, University of Helsinki, Finland
  • 5Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark

Abstract. This work investigates the individual and combined effects of temperature and volatile organic compound precursor concentration on the chemical composition of particles formed in the dark ozonolysis of α-pinene. All experiments were conducted in a 5 m3 Teflon chamber at an initial ozone concentration of 100 ppb and α-pinene concentrations of 10 ppb and 50 ppb, respectively, at constant temperatures of 20 °C, 0 °C, or −15 °C, and at changing temperatures (ramps) from −15 °C to 20 °C and from 20 °C to −15 °C. The chemical composition of the particles was probed using a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS).

A four-factor solution of a Positive Matrix Factorization (PMF) analysis of combined HR-ToF-AMS data from experiments conducted under different conditions is presented. The PMF analysis as well as elemental composition analysis of individual experiments show that secondary organic aerosol particles with the highest oxidation level are formed from the lowest initial α-pinene concentration (10 ppb) and at the highest temperature (20 °C). Higher initial α-pinene concentration (50 ppb) and/or lower temperature (0 °C or −15 °C) result in lower oxidation level of the molecules contained in the particles. With respect to carbon oxidation state, particles formed at 0 °C are more comparable to particles formed at −15 °C than to those formed at 20 °C. A remarkable observation is that changes in temperature during or after particle formation result in only minor changes in the elemental composition of the particles. The temperature at which aerosol particle formation is initiated thus seems to be a critical parameter for the particle elemental composition.

Comparison of the AMS derived estimates of the content of organic acids in the particles based on m/z 44 in the spectra show good agreement with results from off-line molecular analysis of particle filter samples collected from the same experiments. While higher temperatures are associated with a decrease in the absolute mass concentrations of organic acids (R-COOH) and organic acid functionalities (-COOH), the organic acid functionalities account for an increasing fraction of the measured SOA mass at higher temperatures.

Louise N. Jensen et al.

 
Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Louise N. Jensen et al.

Louise N. Jensen et al.

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Short summary
This work targets the chemical composition of alpha-pinene derived secondary organic aerosol formed in the temperature range −15 to 20 °C. Positive Matrix Factorization analysis of data obtained by a High-Resolution Time-of-Flight Aerosol Mass Spectrometer shows that the elemental SOA composition is controlled by initial alpha-pinene concentration and temperature during SOA formation. A significant new finding is that a change in temperature of up to 35 °C after SOA formation has little impact on
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