Research ArticleATMOSPHERIC SCIENCE

On the fate of oxygenated organic molecules in atmospheric aerosol particles

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Science Advances  13 Mar 2020:
Vol. 6, no. 11, eaax8922
DOI: 10.1126/sciadv.aax8922
  • Fig. 1 Mass spectral comparison of laboratory and ambient organic aerosol.

    (A) Mass spectrum (30-s average) of all secondary aerosol compounds generated during an α-pinene ozonolysis experiment in the atmospheric simulation chamber at the Paul Scherrer Institute, measured by the EESI-TOF at a mass loading of ~23 μg m−3 (B) Mass spectrum (30-s average) of all compounds measured by the same instrument in the particle plume observed in Hyytiälä with total mass loadings of ~14 μg m−3 (see fig. S1). An expanded view of the oligomer region (300 to 500 m/z) is shown in the upper right corner. The signal is normalized to the maxima of the highest organic peaks observed (C9H14O5 for Hyytiälä and C9H14O4 for the chamber study). Corresponding mass defect plots for these two spectra are shown in fig. S2.

  • Fig. 2 Time evolution of particle and gas-phase composition for α-pinene ozonolysis.

    (A) α-Pinene injection into the chamber (~35 ppbv) measured by the PTR-TOF-MS and gas-phase evolution of its oxidation products measured by the nitrate CIMS. The measured highly oxygenated molecules show fast production and immediate depletion from the gas phase due to their low volatility. (B) Time evolution of particle phase dimers, grouped by their carbon number. (C) Time evolution of three dimers and one monomer measured in the particle phase showing very distinct behavior despite similar saturation vapor concentrations. (D) Time evolution of particle phase monomers, grouped by their carbon number. All signals are normalized to the maximum signal recorded for the respective ion during the displayed period. All data are taken from experiment 1, except for α-pinene, which is taken from experiment 2 (which has similar initial conditions; see table S1) due to nonavailable PTR-TOF-MS data.

  • Fig. 3 Relative monomer (C5–C10) and dimer (C15–C20) fraction measured by the EESI-TOF to the total signal (sum of all monomers and dimers) for chamber experiment 1.

    The right axis shows wall loss–corrected mass measured by the SMPS.

  • Fig. 4 Mass defect plot of species detected by the EESI-TOF in the SOA produced by α-pinene ozonolysis (experiment 1).

    Mass defect plot of species detected by the EESI-TOF in the SOA produced by α-pinene ozonolysis (experiment 1) color-coded by (A) time of the maximum signal of the respective particle-phase species, (B) individual decay rate of each species (dark gray markers correspond to ions that do not show any decay in the particle), and (C) fraction of remaining signal after 12 hours (after wall loss correction). Symbol areas are sized according to the square root of ion signal at the time when the maximum mass was reached in the chamber.

  • Fig. 5 Time evolution of selected particle and gas-phase species measured during an α-pinene ozonolysis experiment.

    (A) Time evolution of three dimer species in the particle phase measured by EESI-TOF. (B) Time evolution of C10H14–18Ox monomers in the particle grouped by their number of hydrogens. (C and D) Time evolution of C10H18O6 and C10H16O8 species and their potential decomposition products C10H16O5 and C10H14O7. The decay rates of ~0.01 to 0.02 min−1 correspond to the lifetimes of about 50 to 100 min. The potential decomposition products C10H16O5 and C10H14O7 correspond to possible reduction of the hydroperoxide group to a ketone group. (E) PTR-TOF-MS gas-phase measurement of α-pinene (red) and total signal of HOMs measured by the nitrate CIMS (orange). Formic acid (magenta) is measured simultaneously by the PTR-TOF-MS and the iodide CIMS (circles) in the gas phase, with substantial delay suggesting its secondary formation due to decomposition reactions. Propionic acid (or an isomer corresponding to C3H6O2 such as hydroxyacetone or methylacetate) is observed with similar time evolution. Signal of each molecule is normalized to the maximum signal recorded for the respective ion during the displayed period.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/6/11/eaax8922/DC1

    Fig. S1. Real-time particle measurement in Hyytiälä.

    Fig. S2. Wind directions above the canopy and organic mass measured by the ACSM in Hyytiälä.

    Fig. S3. Similarity scores between the α-pinene ozonolysis and ambient Hyytiälä mass spectra from the current study (see Fig. 1) with each other as well as with EESI-TOF mass spectra from source apportionment of summer measurements in Zurich (23) and from laboratory aging of emission from a domestic wood stove.

    Fig. S4. Time evolution of gas-phase species as measured by PTR-TOF-MS (α-pinene) and nitrate CIMS (HOM-grouped based on their number of carbons).

    Fig. S5. Atomic O:C ratio as a function of carbon number for monomer and dimer products.

    Fig. S6. Fraction of signal remaining (calculated as the ratio of the final signal after 12 hours to the signal at the point of the maximum mass concentration for the respective ion) for all species measured by the EESI-TOF plotted against their saturation vapor concentration (logC*).

    Fig. S7. Example of time evolution for two dimer species (C20H32O9 and C19H30O9) measured in the particle by the EESI-TOF, illustrating calculation methods for time of maximum and decay rate.

    Fig. S8. Comparison of EESI-TOF and FIGAERO-I-CIMS.

    Fig. S9. Effect of OH scavenger on monomer and dimer composition.

    Fig. S10. Selected time series from an experiment in which butanol was added as an OH scavenger.

    Fig. S11. Comparison of EESI-TOF and SMPS measurements.

    Table S1. Overview of experimental conditions.

    Table S2. Decay rates and fractions remaining for selected ions as measured by the EESI-TOF.

    Reference (54)

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Real-time particle measurement in Hyytiälä.
    • Fig. S2. Wind directions above the canopy and organic mass measured by the ACSM in Hyytiälä.
    • Fig. S3. Similarity scores between the α-pinene ozonolysis and ambient Hyytiälä mass spectra from the current study (see Fig. 1) with each other as well as with EESI-TOF mass spectra from source apportionment of summer measurements in Zurich (23) and from laboratory aging of emission from a domestic wood stove.
    • Fig. S4. Time evolution of gas-phase species as measured by PTR-TOF-MS (α-pinene) and nitrate CIMS (HOM-grouped based on their number of carbons).
    • Fig. S5. Atomic O:C ratio as a function of carbon number for monomer and dimer products.
    • Fig. S6. Fraction of signal remaining (calculated as the ratio of the final signal after 12 hours to the signal at the point of the maximum mass concentration for the respective ion) for all species measured by the EESI-TOF plotted against their saturation vapor concentration (logC*).
    • Fig. S7. Example of time evolution for two dimer species (C20H32O9 and C19H30O9) measured in the particle by the EESI-TOF, illustrating calculation methods for time of maximum and decay rate.
    • Fig. S8. Comparison of EESI-TOF and FIGAERO-I-CIMS.
    • Fig. S9. Effect of OH scavenger on monomer and dimer composition.
    • Fig. S10. Selected time series from an experiment in which butanol was added as an OH scavenger.
    • Fig. S11. Comparison of EESI-TOF and SMPS measurements.
    • Table S1. Overview of experimental conditions.
    • Table S2. Decay rates and fractions remaining for selected ions as measured by the EESI-TOF.
    • Reference (54)

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