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Auxiliary Material
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This auxiliary material contains: 10 pages, 4 figures, 2 tables
Unique ocean-derived particles serve as a proxy for changes in ocean chemistry
Cassandra J. Gaston,1 Hiroshi Furutani,2† Sergio A. Guazzotti,2‡ Keith R. Coffee,2 Timothy S.
Bates,3 Patricia K. Quinn,3 Lihini I. Aluwihare,1 B. Gregory Mitchell,1 and Kimberly A.
Prather1,2*
1
Scripps Institution of Oceanography, University of California, San Diego, La Jolla CA 92093
USA
2
Dept. of Chemistry and Biochemistry, University of California, San Diego, La Jolla CA 920930314 USA
3
NOAA Pacific Marine Environmental Laboratory, Seattle, WA, 98115 USA
†Current address: Atmosphere and Ocean Research Institute, University of Tokyo, Chiba 277-8564,
Japan
‡Current address: Thermo Fisher Scientific, 355 River Oaks Parkway, San Jose, CA, 95134 USA
Current address: Lawrence Livermore National Laboratory, Livermore, CA, 94550 USA
*Corresponding author: kprather@ucsd.edu, 858-822-5312. Fax: 858-534-7042.
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Details of the INDOEX, ACE-Asia, and CIFEX Field Campaigns
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The duration, sampling platform, ocean basin, latitudinal range, longitudinal range, and
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the relative humidity of the sampling inlet for the Indian Ocean Experiment (INDOEX), the
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Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia), and the Cloud Indirect
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Effects Experiment (CIFEX) are described in Table S1. Furthermore, cruise tracks are depicted
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in Figure S1 for the INDOEX and ACE-Asia field campaigns.
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Comparison of Mg-containing Spectra Obtained with ATOFMS
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Mg+ (m/z +24, 25, 26) is a commonly observed ion using ATOFMS and has been
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associated with other particle sources such as dust and sea salt particles (see Table S2 for a list of
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common ion peak assignments for a given m/z). What makes these Mg-type, ocean-derived
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particles distinct are their characteristic spectra, which are quite different from both sea salt and
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dust. Figure S2 shows representative spectra of sea salt and dust particles containing Mg while
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Figure 2a and 2b in the manuscript shows the Mg-type ocean-derived particle described in this
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paper.
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described in Figure S2 [Guazzotti et al., 2001; Silva et al., 2000]. Dust typically contains ion
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peaks for Al+ (m/z +27), K+ (m/z +39), and, in particular, Fe+ (m/z +56) in addition to Mg+ as
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well as silicates in the negatives. Sea salt is rich in Na+ (m/z +23) and, consequently, has higher
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ion peak intensity than Mg+ in sea salt. The laser desorption/ionization (LDI) process is most
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sensitive to species with lower ionization potential (IP) energies [Fergenson et al., 2001; Gross
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et al., 2000]. Mg has a lower IP (7.646eV) than Fe (7.902eV) and a higher IP in comparison to
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K (4.341eV), Na (5.139eV), Al (5.986eV), and Ca (6.113eV) while the energy provided during
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the LDI process is 4.7eV/photon (at 266nm) [Lide, 2009] producing ~9.4eV for a two photon
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ionization. This means that particles that contain Mg with a combination of these inorganic
Mg+ is typically not the dominant inorganic ion found in the dust or sea salt particles
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species will typically produce spectra with Mg being less intense than these other species. For
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example, as seen in Figure S2a, the Na:Mg ion ratio detected in sea salt particles is (10:1) [Gross
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et al., 2000] while the Na:Mg ion ratio is reversed in these unique particles types.
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Temporal Comparison of Ocean-derived Particles, Dust Particles, Latitude, Atmospheric
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DMS, and Sea Water DMS Concentrations During INDOEX
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The INDOEX field campaign provided a unique opportunity to sample aerosol north of
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the Intertropical Convergence Zone (ITCZ) impacted by continental emissions and south of the
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ITCZ characterized by clean marine conditions. As seen in Figure S3, the percentage of dust
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particles decreases to near zero as the ITCZ, located south of the equator, is crossed. During this
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time period, the percentage of Mg-type particles increases as does DMS concentrations, both
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atmospheric and sea water, and chlorophyll concentrations.
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continental emissions. South of the ITCZ, strong correlations between Mg-type particles and
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atmospheric DMS were observed as discussed in the main body of the paper. Also, as seen in
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Figure S3, the percentage of Mg-type particles increases as the wind speed increases. The right
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panel of Figure S3 shows a representative 48-hour HYSPLIT [Draxler and Rolph, 2003] air
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mass back-trajectory highlighting the air mass history. The air mass back-trajectories highlight
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that the air masses in the southern Indian Ocean were not stagnant suggesting that strong
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correlations between seawater DMS and chlorophyll might not be expected.
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Comparison of Single Particle and Bulk Techniques
This confirms the absence of
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As noted above, ATOFMS is extremely sensitive to inorganic species such as Mg and
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even though high ion peak intensities are observed in the mass spectra, Mg represents a relatively
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small fraction (<1%) of the total particle mass when compared with carbonaceous species [Gross
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et al., 2000]. This means that ATOFMS is very sensitive to changes in chemical mixing state,
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particularly for inorganic species. Figure S4 shows the different types of information that can be
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obtained for chemical mixing state from a bulk analysis versus a single particle perspective.
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Bulk analysis must assume each particle has the same composition for a given size (left panel).
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However, single particle measurements can detect the presence of particles with distinctly
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different compositions (right panel).
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composition is still the same as the average composition of seawater; however, only the single
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particle technique would detect the separation of aerosol populations.
Note that in both scenarios, the average particle
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References
Draxler, R.R., and G.D. Rolph (2003), HYSPLIT (HYbrid Single-Particle Lagrangian Integrated
Trajectory) model access via NOAA ARL READY Website
(http://www.arl.noaa.gov/ready/hysplit4.html), NOAA Air Resources Laboratory, Silver
Spring, MD.
Fergenson, D.P., X.H. Song, Z. Ramadan, J.O. Allen, L.S. Hughes, G.R. Cass, P.K. Hopke, and
K.A. Prather (2001), Quantification of ATOFMS data by multivariate methods, Anal.
Chem., 73 (15), 3535-3541.
Gross, D.S., M.E. Galli, P.J. Silva, and K.A. Prather (2000), Relative sensitivity factors for alkali
metal and ammonium cations in single particle aerosol time-of-flight mass spectra, Anal.
Chem., 72 (2), 416-422.
Guazzotti, S.A., K.R. Coffee, and K.A. Prather (2001), Continuous measurements of sizeresolved particle chemistry during INDOEX-Intensive Field Phase 99, J. Geophys. Res.[Atmos.], 106 (D22), 28607-28627.
Lide, D.R., Ed., CRC Handbook of Chemistry and Physics, CRC Press/Taylor and Francis, Boca
Raton, FL, 2009.
Silva, P.J., R.A. Carlin, and K.A. Prather (2000), Single particle analysis of suspended soil dust
from Southern California, Atmos. Environ., 34, 1811-1820.
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Table S1: Details of the INDOEX, ACE-Asia, and CIFEX Field Campaigns
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Table S2: Assignments of Ion Peaks for a Given Mass-to-Charge
Mass-to-Charge
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Assignment
C+
CH3+
H3O+
Na+
Mg+ (includes isotopes)
Al+, C2H3+, CHN+
NO+
C3 +
K+, C3H3+
Ca+
C3H5+, Na∙H2O+
C2H3O+
C4H2+
Fe+, CaO+
CaOH+, K (H2O)+
Na∙(H2O)2+
Na2O+
Na2OH+, C5H3+
K∙(H2O)2+
Na∙(H2O)3+, C6H5 +
Na2Cl+ (includes isotopes)
C7H7+
Na∙(H2O)4+
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Figure S1: Cruise tracks for INDOEX and ACE-Asia.
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Figure S2: Positive ion mass spectra of representative (a) sea salt and (b) dust particles.
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Figure S3: Left panel shows one hour resolution time series of Mg-type particles (green), dust
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particles (brown line), wind speed (grey line), atmospheric DMS concentrations (black asterisks),
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seawater DMS concentrations (purple crosses), chlorophyll (blue line), and latitude (dotted
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orange line) observed during the INDOEX cruise aboard the RV Ronald Brown.
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shows a representative 48-hour HYSPLIT back trajectory during the INDOEX cruise taken at
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2500 m (green line), 1000 m (blue line), and 500 m (red line).
Right panel
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Figure S4: Traditional filter (bulk) analysis shows the same seawater and air concentrations of
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Mg, Ca, and K by assuming all particles have the exact same composition (left). Single particle
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analysis can reveal distinctions in sea spray aerosol populations (right).
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