Research ArticleATMOSPHERIC SCIENCE

Ion-induced sulfuric acid–ammonia nucleation drives particle formation in coastal Antarctica

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Science Advances  28 Nov 2018:
Vol. 4, no. 11, eaat9744
DOI: 10.1126/sciadv.aat9744
  • Fig. 1 Example of an NPF event at Aboa, Antarctica, 7 January 2015, ~130 km inland.

    (A) Size distribution of 2.25- to 40-nm aerosol particles measured with the Neutral cluster and Air Ion Spectrometer (NAIS). NPF starts around noon (UTC time) and continues for around 7 hours. The particles continue to grow beyond midnight, in 24-hour daylight. (B) Number concentrations of 1.5- to 3-nm (±0.2-nm) particles: Ntot is the total number concentration (±50%) in the size range of 1.5 to 3 nm, measured with the particle size magnifier (PSM); Nions is the small ion concentration (±30%) measured with the NAIS; and Nrec is the calculated neutral cluster concentration from ion-ion recombination. The sum of Nions + Nrec shows that ion-induced nucleation accounts for all particles measured with the PSM during this event. (C) Sulfuric acid (H2SO4), MSA (CH3SO3H), and iodic acid (HIO3) concentrations measured by a nitrate chemical ionization atmospheric pressure interface time-of-flight (CI-APi-TOF) mass spectrometer. Remarkably high sulfuric acid concentrations, ~2 (±1) × 107 molecules/cm3, were recorded during the peak of the NPF event. The uncertainty limits for sulfuric acid indicate the collision limit of sulfuric acid with charger ions (lower error bar) and overestimation of the losses in the inlet tube by a factor of 2 (upper error bar). The mean concentrations were calculated using a calibration factor of 1.195 × 1010 that was obtained with the same 60-cm inlet tube. Very low levels of iodic acid were recorded, and they showed no association with the NPF. The LOD line depicts the limit of detection (3.6 × 104 molecules cm−3) recorded for sulfuric acid. (D) Emission sensitivity for the air masses traveling to Aboa (72-hour back trajectory) in the estimated boundary layer (<600 m). Gray areas depict the sea ice cover, and we see that the air masses originate from the open Southern Ocean. No NPF events were observed from continental air masses or from areas completely covered by sea ice (figs. S2 and S3).

  • Fig. 2 Molecular composition of the negative ion clusters measured by the APi-TOF.

    Negative ion clusters detected (A) before and (B) during an NPF event on 3 January 2015. Both mass spectra are integrated for 180 min. Other event days show similar distributions (fig. S4). Colors indicate negative molecular clusters of nitric acid and other identified compounds with no role in particle formation (black), pure sulfuric acid (red), sulfuric acid–ammonia (blue), and iodic acid–sulfuric acid–ammonia (gray). Open dots depict clusters known to be associated to system-originating impurities or with unknown composition. The largest detected negative cluster contains 10 molecules of sulfuric acid and 3 molecules of ammonia (labeled “10:3”). The area of the circles is proportional to the signal rate (counts s−1).

  • Fig. 3 Comparison to nucleation rates measured in CLOUD.

    Comparison of nucleation rates (unit cm−3 s−1, shown by different colors) with the CLOUD (19). Jgcr parameterization contours at 268 K (−5°C). The CLOUD parameterization assumes a ground-level galactic cosmic ray ionization rate of 1.8 ion pairs cm−3 and no contribution from terrestrial radioactivity, which gives an equilibrium ion pair concentration of about 1100 cm−3 under pristine Antarctic conditions. An agreement between our J1.5 measurements and CLOUD results is obtained for ambient NH3 concentrations between 3 and 30 pptv. On the other hand, without NH3, the CLOUD measurements predict a factor of 10 to 30 lower nucleation rates than we observed. These NH3 levels are consistent with the NH3 fraction measured by the APi-TOF (16).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/11/eaat9744/DC1

    Section S1. Field site and instrumentation

    Section S2. Methods

    Table S1. Data coverage of individual instruments during the FINNARP 2014 campaign.

    Table S2. Sulfuric acid concentration, condensation sink, particle growth rates, and particle formation rates for 3-nm (J3) and 1.5-nm (J1.5) particles determined for NPF events using different methods.

    Fig. S1. Overview of the FINNARP 2014 campaign at Aboa, Antarctica (no flagged data).

    Fig. S2. NPF days.

    Fig. S3. No NPF days.

    Fig. S4. Negative ion composition measured by the APi-TOF.

    Fig. S5. APi-TOF (positive ions) mass defect plot during the observed NPF event on 18 January at Aboa.

    Fig. S6. NAIS size distribution of negative (top) and positive (bottom) ions during the NPF event day when chemical composition of ion was measured in the positive polarity (fig. S5).

    Fig. S7. Number concentrations of 1.5- to 3-nm particles during 1 week of the measurement period (4 to 10 January 2015).

    Fig. S8. The size distribution of 2- to 42-nm particles (top), 0.8- to 42-nm negative (second) and positive (third) ions measured with the NAIS, and the sum of particle concentration measured with the PSM [1.5 to 3 (±0.2) nm; bottom] during the measurement campaign.

    References (2638)

  • Supplementary Materials

    This PDF file includes:

    • Section S1. Field site and instrumentation
    • Section S2. Methods
    • Table S1. Data coverage of individual instruments during the FINNARP 2014 campaign.
    • Table S2. Sulfuric acid concentration, condensation sink, particle growth rates, and particle formation rates for 3-nm (J3) and 1.5-nm (J1.5) particles determined for NPF events using different methods.
    • Fig. S1. Overview of the FINNARP 2014 campaign at Aboa, Antarctica (no flagged data).
    • Fig. S2. NPF days.
    • Fig. S3. No NPF days.
    • Fig. S4. Negative ion composition measured by the APi-TOF.
    • Fig. S5. APi-TOF (positive ions) mass defect plot during the observed NPF event on 18 January at Aboa.
    • Fig. S6. NAIS size distribution of negative (top) and positive (bottom) ions during the NPF event day when chemical composition of ion was measured in the positive polarity (fig. S5).
    • Fig. S7. Number concentrations of 1.5- to 3-nm particles during 1 week of the measurement period (4 to 10 January 2015).
    • Fig. S8. The size distribution of 2- to 42-nm particles (top), 0.8- to 42-nm negative (second) and positive (third) ions measured with the NAIS, and the sum of particle concentration measured with the PSM 1.5 to 3 (±0.2) nm; bottom during the measurement campaign.
    • References (2638)

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