Data Files Accompanying: "Size Dependent Morphology, Phase State, Composition and Water Uptake of Nascent Submicrometer Sea Spray Aerosols During a Phytoplankton Bloom"

Authors: Chathuri P. Kaluarachchi, Victor W. Or, Chamika Madawala, Yiling Lan, Elias S. Hasenecz, Daniel R. Crocker, Clare K. Morris, Kathryn J. Mayer, Jonathan S. Sauer, Christopher Lee, Francesca Malfatti, Mark Thiemens, Elizabeth A. Stone, Timothy H. Bertram, Christopher D. Cappa, Vicki H. Grassian, Kimberly A. Prather, and Alexei V. Tivanski 
Journal: ACS Earth and Space Chemistry

Contact: Tivanski, Alexei. V., alexei-tivanski@uiowa.edu, Department of Chemistry, University of Iowa, Iowa City, Iowa 52242

Cite as:
Chathuri P. Kaluarachchi, Victor W. Or, Chamika Madawala, Yiling Lan, Elias S. Hasenecz, Daniel R. Crocker, Clare K. Morris, Kathryn J. Mayer, Jonathan S. Sauer, Christopher Lee, Francesca Malfatti, Mark Thiemens, Elizabeth A. Stone, Timothy H. Bertram, Christopher D. Cappa, Vicki H. Grassian, Kimberly A. Prather, and Alexei V. Tivanski (2021): Data from: Size Dependent Morphology, Phase State, Composition and Water Uptake of Nascent Submicrometer Sea Spray Aerosols During a Phytoplankton Bloom. In Center for Aerosol Impacts on Chemistry of the Environment (CAICE) Collection. UC San Diego Library Digital Collections.
DOI: https://doi.org/10.6075/J04748D9

Folder organization: Morphological types, phase states, water uptake information from each bloom designated day separated into three data files, Bulk organic and inorganic mass fraction data, Chl-a and HB concentrations data.


Method: Sea spray aerosols (SSA) generation for atomic force microscopy (AFM) and AFM photothermal infrared spectroscopy (AFM-PTIR). SSA were generated from a wave-simulation channel facility containing filtered seawater from the southern coast of California during the summer-2019 Sea Spray Chemistry And Particle Evolution (SeaSCAPE) study. The filtered seawater was obtained by initially passing the collected seawater through an aluminum screen to remove large marine detritus (e.g., seaweed), followed by passing through a pre-cleaned Nitex nylon 50-µm mesh to remove larger particulates and zooplankton. A phytoplankton bloom in the wave-simulation channel was induced by adding nutrients following previous approaches. During the SeaSCAPE study, the phytoplankton bloom cycle occurred from July 25th until August 14th. During the course of the bloom cycle, concentrations of chlorophyll-a (Chl-a) and heterotrophic bacteria (HB) were measured daily. Chl-a concentration was measured using a Sea Bird Scientific ECO-Triplet-BBFL2 sensor and Turner AquaFluor device. HB counts were measured using BD FACSCanto IITM flow cytometer.
A micro-orifice uniform deposit impactor (MOUDI; MSP, Inc., model 110) was used to deposit individual submicrometer SSA particles onto hydrophobically treated (using Rain-x) silicon substrates (Ted Pella, Inc.) at ca 80% relative humidity (RH). MOUDI stages 7, 8, and 9 were used, which corresponds to the 50% cut-off aerodynamic diameter ranges of 0.32 - 0.56 µm, 0.18 - 0.32 µm, and 0.10 - 0.18 µm, respectively. The substrate-deposited SSA samples were stored in clean Petri dishes and kept inside a laminar flow hood (NuAire, Inc., NU-425-400) at ambient temperature (20-25˚C) and pressure prior to the AFM experiments. The SSA samples collected during July 26th (pre-bloom), August 2nd (peak-bloom), and August 6th (post-bloom) days were selected to investigate the relative distribution of the SSA morphology, composition, phase state, water uptake, and organic volume fraction for the core-shell particles.

Single particle AFM morphology and organic volume fraction. 
A molecular force probe 3D AFM (Asylum Research, Santa Barbara, CA) is used for imaging individual substrate-deposited SSA at 20% RH and ambient temperature (20 - 25˚C). A custom-made humidity cell was used to control RH with a range between 3% and 97%. For each RH value, a waiting time of at least 10 mins was allocated prior to AFM measurements to ensure the particles are in the thermodynamic equilibrium with the surrounding water vapor at corresponding RH. Silicon nitride AFM tips (MikroMasch, model CSC37, tip radius of curvature ~10 nm, nominal spring constant 0.5 - 0.9 N/m) were used for the imaging and force spectroscopy measurments. AFM AC mode imaging was used to collect 3D height and phase images of individual SSA to determine their morphology, size, and quantify the organic volume fraction (OVF) for core-shell SSA. AFM phase images show degrees of phase shift with respect to the original AFM tip oscillations, which is related to the differences in viscoelastic nature within the SSA. The OVF is defined as the ratio of the shell volume to the total particle volume. The Igor Pro single particle analysis was used to measure the total particle volume from the AFM height image. The total particle volume was used to quantify corresponding volume-equivalent diameter of the particle. For individual core-shell SSA, the phase image was used to determine the shell region and corresponding AFM height image was utilized to quantify the shell volume. Assuming the core is predominantly inorganic, and shell is largely organic, single particle OVF is reflective of the amount of organic relative to inorganic present in the core-shell SSA. The OVF values were recorded as average from values obtained on individual core-shell SSA with one standard deviation for the pre-bloom, peak-bloom, and post-bloom days at three volume-equivalent diameter ranges of 0.10 - 0.18 µm, 0.18 - 0.32 µm and 0.32 - 0.60 µm. For the OVF study, at least 20 individual core-shell SSA were studied for each day. Relative distributions of five main SSA morphological categories identified in this work (rounded, core-shell, prism-like, rod, and aggregates) were recorded for the pre-bloom, peak-bloom, and post-bloom days at three volume-equivalent diameter ranges of 0.10 - 0.18 µm, 0.18 - 0.32 µm and 0.32 - 0.60 µm. For the morphological study, 100-120 individual particles were investigated for each day.

Single particle AFM water uptake and phase state. 
The water uptake was measured by recording on a single particle basis 3D growth factor at 80% RH. The growth factor is defined as the ratio of the volume-equivalent diameter of an individual SSA measured using AFM height imaging at 80% RH over the corresponding volume-equivalent diameter recorded at 20% RH. The water uptake measurements were performed on 5 - 10 individual SSA with the most abundant morphologies (core-shell and rounded) at the highest relative occurrence size range (0.32 - 0.60 µm for core-shell and 0.10 - 0.18 µm for rounded) during each sampling day. The GF values were reported as an average and one standard deviation for each SSA morphological type.
The phase state identification at 20% and 60% RH were performed using AFM force spectroscopy under ambient temperature (20-25˚C) and pressure for each of the five main SSA morphologies using previously reported method. AFM force spectroscopy measurements were performed to measure forces acting on the AFM tip versus tip-sample separation (i.e., force plots) with the maximum force of 20 nN and scan rate of 1 Hz. At least five force plots were collected at several different locations on an individual particle at 20% and 60% RH. The collected force plots were then used to quantify the viscoelastic response distance (VRD, nm) and the relative indentation depth (RID, the ratio of the indentation distance over the particle height) for an individual particle. The VRD values measured on SSA in semisolid phase state were recorded as an average and one standard deviation. Approximately 20 individual SSA for each of the five main morphologies were investigated. The VRD values and phase state identification for the shell of core-shell SSA and rounded particles were recorded at three volume-equivalent diameter ranges of 0.10 - 0.18 µm, 0.18 - 0.32 µm and 0.32 - 0.60 µm for each sampling day. As no apparent size-dependent phase state was observed for the prism-like, rod, and aggregates morphologies, the VRD results were recorded for the entire volume-equivalent size range of 0.10 - 0.60 µm at 20% and 60% RH over each sampling day.

Single particle AFM photothermal infrared spectroscopy (AFM-PTIR). 
AFM-PTIR measurements were conducted using a commercial nanoIR2 (Bruker, Santa Barbara, CA) microscope equipped with a tunable mid-IR quantum cascade laser (QCL) and a tunable mid-IR optical parametric oscillator laser (OPO). Experiments were performed at 20% RH and ambient temperature (23-26˚C) on SSA samples collected on MOUDI stages 7, 8, and 9 during July 26th (pre-bloom) and August 2nd (peak-bloom) days. AFM height images were collected in tapping mode at a scan rate of 0.5 Hz using silicon nitride probes with a chromium-gold coating (HQ: NSC19/CR-AU, MikroMasch, tip radius of curvature of 35 nm, and a nominal spring constant range of 0.05-2.3 N/m). PTIR spectra were collected at a preselected tip-localized position across the sample surface with a nominal spatial resolution below 35 nm and a spectral resolution of 8 cm-1 (OPO) and 5 cm-1 (QCL), while co-averaging over 128 laser pulses. To account for any possible substrate PTIR signal contribution, a reference spectrum was taken on the substrate and subtracted from all corresponding spectra obtained for individual particles. Approximately 10 individual SSA with core-shell and rounded morphologies were investigated. For core-shell SSA, spectra were taken at the core and shell particle regions, while for the rounded SSA spectra were taken at approximate center of the particle.

Bulk measurements of organic and inorganic mass fraction. 
SSA particles were collected at 74 - 96% RH using a five stage SIOUTAS Personal Cascade Impactor at flow rate of 9 L/min (PCIS, SKC model 225 - 370' with 50% cut-off aerodynamic diameter ranges for each impactor stage of < 0.25 µm, 0.25 - 0.50 µm, 0.50 - 1.0 µm, 1.0 - 2.50 µm, and > 2.5 µm) onto substrates consisting of pre-baked 25 mm aluminum (Al) foil disks for the top four stages and pre-baked 37 mm quartz fiber filter (QFF, PALL Life Sciences) for the lowest stage. Samples were collected between 24 - 44 hours depending on daily conditions. All samples were stored frozen (-20˚C) until the analysis. Organic carbon (OC) was measured using thermal optical analyzer (Sunset Laboratories, Forest Grove, OR), as described previously. The common inorganic ions were separated and quantified via high-performance ion exchange chromatography with conductivity detection (Dionex ICS5000, Sunnyvale, CA). Substrates were sub sampled using a stainless steel punch and extracted in 4 mL of ultrapure (>18.2 M-*cm, Thermo Barnstead EasyPure II). Quartz fiber filter were extracted with 30:40:30 minutes of shaking-sonication-shaking, while Al substrates were extracted by shaking for 100 minutes. All extracts were filtered (0.45 µm polypropylene Whatman) prior to analysis. Anions and cations were identified against authentic standards (Dionex) and quantified with seven point calibration curves. Inorganic mass was estimated as sea salt by converting the mass of sodium measured to the mass of sea salt using the sodium/sea salt ratio previously determined from seawater salt composition.