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Volume 18, issue 4 | Copyright
Atmos. Chem. Phys., 18, 2883-2898, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 28 Feb 2018

Research article | 28 Feb 2018

α-Pinene secondary organic aerosol at low temperature: chemical composition and implications for particle viscosity

Wei Huang1,2, Harald Saathoff1, Aki Pajunoja3, Xiaoli Shen1,2, Karl-Heinz Naumann1, Robert Wagner1, Annele Virtanen3, Thomas Leisner1, and Claudia Mohr1,4 Wei Huang et al.
  • 1Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany
  • 2Institute of Geography and Geoecology, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
  • 3Department of Applied Physics, University of Eastern Finland, Kuopio, 80101, Finland
  • 4Department of Environmental Science and Analytical Chemistry, Stockholm University, Stockholm, 11418, Sweden

Abstract. Chemical composition, size distributions, and degree of oligomerization of secondary organic aerosol (SOA) from α-pinene (C10H16) ozonolysis were investigated for low-temperature conditions (223K). Two types of experiments were performed using two simulation chambers at the Karlsruhe Institute of Technology: the Aerosol Preparation and Characterization (APC) chamber, and the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) chamber. Experiment type 1 simulated SOA formation at upper tropospheric conditions: SOA was generated in the AIDA chamber directly at 223K at 61% relative humidity (RH; experiment termed cold humid, CH) and for comparison at 6% RH (experiment termed cold dry, CD) conditions. Experiment type 2 simulated SOA uplifting: SOA was formed in the APC chamber at room temperature (296K) and <1% RH (experiment termed warm dry, WD) or 21% RH (experiment termed warm humid, WH) conditions, and then partially transferred to the AIDA chamber kept at 223K, and 61% RH (WDtoCH) or 30% RH (WHtoCH), respectively. Precursor concentrations varied between 0.7 and 2.2ppm α-pinene, and between 2.3 and 1.8ppm ozone for type 1 and type 2 experiments, respectively. Among other instrumentation, a chemical ionization mass spectrometer (CIMS) coupled to a filter inlet for gases and aerosols (FIGAERO), deploying I as reagent ion, was used for SOA chemical composition analysis.

For type 1 experiments with lower α-pinene concentrations and cold SOA formation temperature (223K), smaller particles of 100–300nm vacuum aerodynamic diameter (dva) and higher mass fractions (>40%) of adducts (molecules with more than 10 carbon atoms) of α-pinene oxidation products were observed. For type 2 experiments with higher α-pinene concentrations and warm SOA formation temperature (296K), larger particles ( ∼ 500nm dva) with smaller mass fractions of adducts (<35%) were produced.

We also observed differences (up to 20°C) in maximum desorption temperature (Tmax) of individual compounds desorbing from the particles deposited on the FIGAERO Teflon filter for different experiments, indicating that Tmax is not purely a function of a compound's vapor pressure or volatility, but is also influenced by diffusion limitations within the particles (particle viscosity), interactions between particles deposited on the filter (particle matrix), and/or particle mass on the filter. Highest Tmax were observed for SOA under dry conditions and with higher adduct mass fraction; lowest Tmax were observed for SOA under humid conditions and with lower adduct mass fraction. The observations indicate that particle viscosity may be influenced by intra- and inter-molecular hydrogen bonding between oligomers, and particle water uptake, even under such low-temperature conditions.

Our results suggest that particle physicochemical properties such as viscosity and oligomer content mutually influence each other, and that variation in Tmax of particle desorptions may have implications for particle viscosity and particle matrix effects. The differences in particle physicochemical properties observed between our different experiments demonstrate the importance of taking experimental conditions into consideration when interpreting data from laboratory studies or using them as input in climate models.

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