Data Files Accompanying: “The effects of atmospheric heterogeneous aging on nascent sea spray aerosols physicochemical properties”

Authors: Chathuri P. Kaluarachchi, Victor W. Or, Yiling Lan, Elias S. Hasenecz, Deborah Kim, Chamika Madawala, Glorianne Dorce, Kathryn J. Mayer, Jonathan S. Sauer, Christopher Lee, Christopher D. Cappa, Timothy H. Bertram, Elizabeth A. Stone, 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:
Kaluarachchi, Chathuri P.; Or, Victor W.; Lan, Yiling; Hasenecz, Elias S.; Kim, Deborah; Madawala, Chamika K.; Dorce, Glorianne; Mayer, Kathryn J.; Sauer, Jonathan S.; Lee, Christopher; Cappa, Christopher D.; Bertram, Timothy H.; Stone, Elizabeth A.; Grassian, Vicki H.; Tivanski, Alexei V. (2023). Data from: The effects of atmospheric heterogeneous aging on nascent sea spray aerosols physicochemical properties. In Center for Aerosol Impacts on Chemistry of the Environment (CAICE). UC San Diego Library Digital Collections. https://doi.org/10.6075/J09S1R6B

DOI: https://doi.org/10.6075/J09S1R6B

Folder organization: Morphological types, phase states, water uptake, Bulk organic and inorganic mass fraction data, PTIR data

Method: Nascent and heterogeneously aged SSA generation and collection for offline analysis. Nascent SSA (nSSA) were generated throughout a phytoplankton bloom from a wave-simulation channel facility contained filtered seawater from the southern coast of California, during the Sea Spray Chemistry And Particle Evolution (SeaSCAPE) 2019 study. A micro-orifice uniform deposit impactor (MOUDI; MSP, Inc., model 110) at a flow rate of 30 L/min was used to deposit individual submicrometer nSSA onto hydrophobically coated (Rain-X) silicon substrates (Ted Pella, Inc.) at ca 80% relative humidity (RH). Additional details of the nSSA generation and deposition can be found elsewhere. A potential aerosol mass oxidation flow reactor (PAM-OFR, Aerodyne Inc) was used to produce hydroxyl (OH) radicals, which can simulate atmospheric heterogeneous aging of aerosols with atmospheric time-equivalent aging from a fraction of a day to several weeks.2, 45, 46 Here, by using the PAM-OFR, heterogeneously aged SSA (hetSSA) were generated by exposing nSSA to OH radicals (average concentration of ~ 5.9 x 1011 molecules cm-3), which correspond to 4-5 days of atmospheric aging. The PAM-OFR sampled nSSA from headspace of the wave-simulation channel to generate hetSSA. However, in addition to hetSSA, new particles formation (i.e., secondary marine aerosols, SMA, typical particle diameter < 100 nm) was also observed, likely as a result of oxidation and condensation of volatile organic compounds from the wave-simulation channel headspace. In the present work, atomic force microscopy (AFM) single particle analysis was limited to particle sizes above 100 nm, thus largely excluding SMA particles. Additional details of the wave-channel experiment and generation of nSSA and hetSSA during the SeaSCAPE 2019 study can be found elsewhere. The generated hetSSA were deposited onto hydrophobically coated silicon substrates using a MOUDI (MSP, Inc., model 125R, flow rate 10 L/m) at ca 20% RH. The MOUDI stages 7, 8 and 9 were used that correspond to 50% cut-off aerodynamic diameter range of 0.32 − 0.60, 0.18 − 0.32, and 0.10 − 0.18 µm, respectively. All 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 AFM experiments. For the purpose of comparison, both nSSA and hetSSA collected on the same sampling day (peak of the bloom, August 2nd) over the same size ranges as determined by AFM were studied.

AFM imaging and organic volume fraction quantification on hetSSA. Particle locations for single particle imaging were selected in a completely random and unbiased manner. A molecular force probe 3D AFM (Asylum Research, Santa Barbara, CA) was used for imaging individual substrate-deposited hetSSA at ~20% RH and ambient temperature (20 − 25°C) as described in prior studies. A custom-made humidity cell was used to control RH with a range between 20% − 80%. Prior to the AFM measurements at a particular RH, at least 10 minutes of waiting time was allocated to ensure that hetSSA are in thermodynamic equilibrium with surrounding water vapor. Silicon nitride AFM tips (MikroMasch, model CSC37, typical tip radius of curvature of ~10 nm, nominal spring constant of 0.5 − 0.9 N/m) were used for the imaging and force spectroscopy measurments. AFM AC (intermittent contact) mode imaging was used to collect 3D height and phase images of individual hetSSA to determine their morphology, volume-equivalent diameter, and to quantify the organic volume fraction (OVF) and organic coating thickness (OCT) for core-shell hetSSA, as described in prior studies. The OVF is defined as the ratio of the shell volume (assumed predominantly organic) to the total particle volume, while the OCT represents the projected thickness of organic coating around the inorganic core. By assuming the  core is predominantly inorganic, the single particle OVF will represent the amount of organic present in the particle relative to the total particle volume. For the morphological analysis, approximately 100 individual hetSSA were investigated, while for the OVF and OCT analysis, approximately 20 individual core-shell hetSSA were investigated. The relative abundance (i.e., an average and one standard deviation for fraction of particles) of identified main morphological categories (rounded, core-shell, prism-like, rod-shell, and aggregate), and the average and one standard deviation of OVF and OCT values 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. The observed hetSSA morphology, OVF and OCT were compared with nSSA sample collected on same sampling day over the same three size ranges.

AFM measurements of hetSSA water uptake and phase state. The analysis of 3D growth factor (GF) at 80% RH was employed to quantify the water uptake properties of hetSSA on a single particle basis. The GF is defined as the ratio of the volume-equivalent diameter of an individual SSA at 80% RH over the corresponding volume-equivalent diameter recorded at 20% RH, where higher values indicative of the presence of more hygroscopic chemical components. The GF measurements were performed on ~10 individual core-shell and rounded hetSSA at their highest relative occurrence size range of 0.32 − 0.60 µm and 0.10 − 0.18 µm, respectively, and the values were reported as an average and one standard deviation. The AFM force spectroscopy was employed to identify the phase state at 20% and 60% RH under ambient temperature (20−25°C) and pressure for hetSSA with the most abundance morphologies (i.e., core-shell, rounded) using previously reported method. The maximum force of 20 nN and scan rate of 1 Hz were used. At least five force plots were collected by probing at shell region of core-shell and rod-shell hetSSA, and at approximately center of rounded hetSSA.1 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 single particle phase state identification was conducted using the established framework from VRD and RID measurements, as described in prior studies. The VRD values measured on hetSSA in semisolid phase state were recorded as an average and one standard deviation. Approximately 10 or more individual hetSSA for each morphology were investigated. The VRD values, and relative abundance (i.e., an average and one standard deviation for fraction of particles) of phase states for the shell of core-shell SSA and rounded particles were recorded at three volume-equivalent diameter ranges of 0.10 − 0.18, 0.18 − 0.32, and 0.32 − 0.60 µm. The observations on phase states and water uptake of hetSSA were compared with nSSA results reported previously.

Since the total number of individual particles that can be practically studied with AFM is limited, we utilized a statistical probability distribution analysis to assess the statistical significance of the AFM based morphology and phase states measurements.1 The detail description about the approach can be found elsewhere. Briefly, the probability distributions associated with the likelihood of sampling one of the five morphologies, or one of the three phase states, were generated using a self-coded Monte Carlo-like simulation method for a “true” population of 10,000 particles. The average with one standard deviation for the fraction of particles from each morphological type or phase states were obtained by fitting the probability distribution plots with the Gaussian function. The results were recorded for nSSA and hetSSA samples as a function of RH, and volume-equivalent diameter range.

AFM-PTIR measurements of hetSSA composition. AFM photothermal infrared (AFM-PTIR) spectroscopic measurements were collected using a commercial AFM-IR microscope (nanoIR2, Bruker) with a tunable mid-IR quantum cascade laser (QCL MIRcat-QT, Daylight solutions). Images and spectra were collected at ~20-30% RH and ambient temperature (23 − 26 °C) and pressure on hetSSA samples deposited on silicon substrates placed on MOUDI stages 7, 8 and 9 correspond to 50% cut-off aerodynamic diameter range of 0.32 − 0.60, 0.18 − 0.32, and 0.10 − 0.18 µm, respectively. Analyses were conducted using silicon nitride probes with a chromium-gold coating (HQ: NSC19/CR-AU, MikroMasch, typical tip radius of curvature 35 nm, and a nominal spring constant range of 0.05 − 2.3 N/m). AFM imaging was conducted in tapping mode at a scan rate of 0.5 Hz. AFM-PTIR spectra were collected with a nominal spatial resolution below 35 nm and a spectral resolution of 5 cm-1, co-averaging over 128 laser pulses per wavenumber. A reference spectrum was taken on the substrate and subtracted from all corresponding spectra obtained on individual particles. For core-shell hetSSA, spectra were taken at the core and shell particle regions, while for rounded hetSSA spectra were taken at an approximate center of each particle. Even accounting for differences in morphology, the large diversity between hetSSA is reflected in large variances between particles. As such, spectral features are not to be interpreted quantitatively, and these analyses only qualitatively demonstrate the presence of a particular set of functional groups.

Bulk measurements of nSSA and hetSSA size-dependent organic and inorganic mass fractions. For these measurements, nSSA and hetSSA samples were collected simultaneously using five stage SIOUTAS Personal Cascade Impactors (PCIS, SKC model 225 – 370; 50% aerodynamic diameter range cut-off for each stage). The top four stages consisted of pre-baked 25 mm Al foil disks (0.25 – 0.50, 0.50 – 1.0, 1.0 – 2.5, and > 2.5 µm) and the last stage a pre-baked 37 mm quartz fiber filter (QFF, PALL Life Sciences, < 0.25 µm). Representative nSSA were collected directly from the wave flume and hetSSA by first oxidizing in the PAM-OFR using the conditions described above prior to collection. Flow rates of 9 L/min and 74 – 96% RH were maintained, and all samples were stored frozen at -20 °C until the analysis. Organic carbon (OC) was measured via a thermal optical analyzer (Sunset Laboratories, Forest Grove, OR) and common inorganic ions were separated and quantified via high-performance ion exchange chromatography with conductivity detection (Dionex ICS5000, Sunnyvale, CA). A stainless steel punch was used to sub sample substrates, which were subsequently extracted in 4 mL of ultrapure water (>18.2 MΩ·cm, Thermo Barnstead Easy Pure II) and filtered (0.45 μm polypropylene, Whatman). Inorganic mass was estimated as sea salt using the measured mass of sodium converted to the mass of sea salt via a sodium/sea salt ratio of 3.26, as described previously.