Research ArticleATMOSPHERIC SCIENCE

Observations of biogenic ion-induced cluster formation in the atmosphere

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Science Advances  25 Apr 2018:
Vol. 4, no. 4, eaar5218
DOI: 10.1126/sciadv.aar5218
  • Fig. 1 Classification of the charged cluster formation events.

    Classification was performed using NAIS surface plots and time series of ions concentration in various size ranges, including 1.5 to 2 nm, 2 to 3 nm, and 3 to 5 nm. (A) Nonevent evening on 12 April. (B) Minimum growth event on 21 April. (C) Medium growth event on 12 May. (D) Maximum growth event on 8 May.

  • Fig. 2 Build-up process of naturally negatively charged HOMs.

    (A) Averaged time evolution of the mass spectra calculated from all 25 event evenings between 1600 and 0000 (local time, UT +2). The solid line and corresponding diamonds illustrate the molecular growth rate resulting from the HOMs build-up process. (B) Mass defect plot for the cluster formation event detected on 20 April. The mass defect, that is, the difference between the exact mass and the nominal mass, is shown on the ordinate. The area of the dots is proportional to the intensity of the observed signal, and the color scale indicates the time at which each of the three mass spectra was measured. The presence of HOM monomers, dimers, and trimers is evidenced on the mass defect plot and their progressive appearance from 1930 to 2130. By contrast, clusters resulting from based-stabilized nucleation of H2SO4 with NH3 or amines are not observed at any time.

  • Fig. 3 Relationship between ion and mass spectrometers observations.

    (A) Normalized HOM dimers signal as a function of 1.44-nm negative ion number concentration. Concentrations and signal intensities are 1-hour averages from all event evenings between 1600 and 0000. (B) Same as (A) with HOM trimers and 1.66-nm negatively charged clusters. (C) Averaged time series of the HOM dimers signal normalized by total ion count (TIC) and formation rate of 1.5-nm negatively charged clusters on event evenings. Black circles represent the median of the normalized HOM dimers signal, whereas lower and upper limits of the error bars represent the 25th and 75th percentiles, respectively.

  • Fig. 4 Insights into the identification of the charged HOMs involved in the formation of negatively charged clusters.

    Normalized signals of (A) non-nitrate and (B) organonitrate HOM dimers as a function of 1.44-nm negative ion number concentration. Concentrations and signal intensities are 1-hour averages from all event evenings between 1600 and 0000.

  • Fig. 5 The effect of various parameters on HOMs production and subsequent ion cluster formation.

    Throughout, colors indicate evening type, that is, nonevent (black) or Maximum growth events (magenta). In (A) to (C), when not specified, reported values are medians calculated over all the evenings belonging to each class. (A) Global radiation (left ordinate) and temperature (right ordinate). (B) Ozone (left ordinate) and monoterpene (right ordinate) concentrations. In addition to median concentrations (triangles), the 25th and 75th percentiles are also reported for monoterpene concentration, corresponding respectively to the lower and upper limits of the error bars. (C) CS (left ordinate) and relative humidity (right ordinate). (D) Proxy for the concentration of monoterpene ozonolysis products. Markers stand for median values, whereas lower and upper limits of the error bars represent the 25th and 75th percentiles, respectively.

  • Table 1 Characteristics of the observed evening events.

    All 25 events were classified into three groups (Minimum, Medium, and Maximum growth events) based on the size of the clusters at the end of the growth process (second column). The number of events in each class is indicated in the first column. Cluster ion (1.5 nm) formation rates (J1.5) and cluster growth rate in the range of 1.5 to 3 nm (GR1.5–3) are reported in the third and fourth columns, respectively. The reported values are given as mean ± 1σ, either calculated from all events or from events of the specified type.

    Type of events (frequency)Final cluster sizeEmbedded Image (×10−1 cm−3)GR1.5−3 (nm hour−1)
    All events2.6 ± 2.32.8 ± 1.4
    Minimum growth events (18)<3 nm2.1 ± 1.62.5 ± 1.3
    Medium growth events (4)Between 3 and 4 nm3.5 ± 2.73.2 ± 0.9
    Maximum growth events (3)>4 nm5.5 ± 3.94.0 ± 2.1

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/4/eaar5218/DC1

    fig. S1. Ion cluster formation rates.

    fig. S2. Time of sunset and beginning and event peak times for each of the 25 events.

    fig. S3. Naturally charged HOM dimers and trimers.

    fig. S4. Naturally charged HOM monomers.

    fig. S5. Sulfuric acid concentration.

    fig. S6. Non-nitrate and organonitrate HOM dimers.

    fig. S7. Conditions favoring HOMs production and subsequent ion cluster formation.

    fig. S8. Evolution of the APi-TOF TIC during the course of the measurement campaign.

    table S1. Relationship between the observations of the ion and mass spectrometers.

    table S2. Characterization of the active cluster formation period.

    table S3. Subsets of compounds representative of non-nitrate and organonitrate HOM dimers.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Ion cluster formation rates.
    • fig. S2. Time of sunset and beginning and event peak times for each of the 25 events.
    • fig. S3. Naturally charged HOM dimers and trimers.
    • fig. S4. Naturally charged HOM monomers.
    • fig. S5. Sulfuric acid concentration.
    • fig. S6. Non-nitrate and organonitrate HOM dimers.
    • fig. S7. Conditions favoring HOMs production and subsequent ion cluster formation.
    • fig. S8. Evolution of the APi-TOF TIC during the course of the measurement campaign.
    • table S1. Relationship between the observations of the ion and mass spectrometers.
    • table S2. Characterization of the active cluster formation period.
    • table S3. Subsets of compounds representative of non-nitrate and organonitrate HOM dimers.

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