Supplementary Information Soot superaggregates from flaming wildfires and their direct radiative forcing

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1 Supplementary Information Soot superaggregates from flaming wildfires and their direct radiative forcing Authors: Rajan K. Chakrabarty 1,2, Nicholas D. Beres 2, Hans Moosmüller 2, Swarup China 3, Claudio Mazzoleni 3, Manvendra K. Dubey 4, Li Liu 5, & Michael I. Mishchenko 5 Affiliations: 1 Department of Energy, Environmental & Chemical Engineering, Washington University in St. Louis, St. Louis, MO 63130, USA. 2 Desert Research Institute, Nevada System of Higher Education, Reno, Nevada, USA 3 Atmospheric Sciences Program, Michigan Technological University, Houghton, Michigan, USA 4 Earth System Observations, Los Alamos National Laboratory, Los Alamos, New Mexico, USA 5 NASA Goddard Institute for Space Studies, New York, NY 10025, USA The Supplementary Information contains Supplementary Methods, Figures S1 to S4 and Supplementary Table S1. 1

2 Supplementary Methods Polar compound analysis (including levoglucosan). For organic compound speciation all filters were extracted by accelerated solvent extraction (Dionex ASE 300 Accelerated Solvent Extrator) with dichloromethane followed by acetone. Several isotopically labeled internal standards were added to each filter sample prior to extraction, includeing: hexanoic-d 11 acid, benzoic-d 5 acid, succinic-d 4 acid, adipic-d 10 acid, suberic-d 12 acid, levoglucosan-d 7, homovanillic-2,2-d 2 acid, myristic-d 27 acid, heptadecanoic-d 33 acid, oleic-9,10-d 2 acid, tetradecanedioic-d 24 acid, and cholesterol-2,2,3,4,4,6-d 6. These extracts were then combined and concentrated by rotary evaporation followed by moisture filtered ultra-high purity (UHP) nitrogen blow down to 100µl under moisture filtered UHP nitrogen and transferred to 300µl silanized glass inserts (National Scientific Company, Inc.). Samples were further evaporated to 50µl, and then 25µl of pyridine, 25µl acetonitrile and 150µl of BSTFA with 1% TMCS [N, O-bis (trimethylsilyl) trifluoroacetamide with 1% trimethylchlorosilane (Pierce)] were added. These derivatizing reagents convert the polar compounds into their trimethylsilyl derivatives for analysis of organic acids, methoxyphenols, and levoglucosan. The deactivated glass insert containing the sample was put into a 2ml vial and sealed. The sample was then placed into a thermal plate (custom made) containing individual vial wells at 70ºC for 2 hours. The calibration solutions were freshly prepared and derivatized just prior to the analysis of each sample set. All samples were analyzed by gas chromatography interfaced with mass spectrometry (GC/MS) within 18 hours to avoid degradation. The samples were analyzed by electron impact ionization GC/MS technique using a Varian CP-3400 gas chromatograph with a model CP-8400 Auto-sampler and interfaced to a Varian 4000 Ion Trap Mass Spectrometer. 2

3 Supplementary Figure S1: 3-day back trajectories of air parcels originating from the MCOH station in Maldives. The trajectories were obtained from the NOAA HYSPLIT model described in All of the 3 day back trajectories ended at the date shown, in Year-2012, 00 UTC 3

4 Supplementary Figure S2: T-matrix calculations of scattering and absorption crosssections of aggregates as functions of size (number of monomers) and fractal dimension D f. Shaded regions represent the upper and lower bound values for D f in the range between 1.8 and 3.0. The calculations used mean refractive index = i, monomer diameter 50 nm, and a wavelength = 550 nm. 4

5 Supplementary Figure S3: T-matrix calculations of scattering and absorption crosssections of D f =2.6 aggregates and superaggregates as a function of size (number of monomers) The calculations used mean refractive index = i, monomer diameter 50 nm, and a wavelength = 550 nm. Monomer number = 400 corresponds to aggregate mobility diameter 1µm. Beyond 1 µm is the superaggregate regime. 5

6 Supplementary Figure S4: Volume-equivalent Mie theory calculations of scattering and absorption cross-sections of aggregates as functions of size (number of monomers) The calculations used mean refractive index = i, monomer diameter 50 nm, and a wavelength = 550 nm. 6

7 Supplementary Table S1: Major polar organic compounds and their mass concentrations identified in aerosol filter samples from the Nagarhole National Forest Fire during March 2-3, Mar/02 pm - Mar/03 am Mar/03 am - Mar/03 pm Compound (ng/m3) (ng/m3) Palmitic Acid (c16) Myristic Acid (c14) Stearic Acid (c18) Pentadecanoic Acid (c15) Decanoic Acid (c10) Dodecanoic (lauric) Acid (c12) Succinic Acid (d-c4) Hexanedioic (adipic) Acid (d-c6) Methyladipic Acid (d-c6) Nonanoic Acid (c9) Phthalic Acid Methylglutaric (d-c5) Undecanoic Acid (c11) Levoglucosan Heptadecanoic Acid (c17) Tridecanoic Acid (c13) Traumatic Acid Azelaic Acid (d-c9) Glutaric Acid (d-c5) Octanoic Acid (c8) Cis-Pinonic Acid Heptanedioic (Pimelic) Acid (d-c7) Suberic Acid (d-c8) Pimaric Acid Me-Succinic Acid (d-c4) Syringaldehyde Sebacic Acid (d-c10) M-Toluic Formyl-Guaiacol (Vanillin) Undecanedioic Acid (d-c11) Myristoleic Acid Oxodehydroabietic Acid Me-Guaiacol Syringol Isophthalic Acid Acetovanillone Vanillic Acid Oleic Acid Nonadecanoic Acid (c19) Mannosan Maleic Acid Isostearic Acid Hexanoic Acid (c6) ,11-Undecanedicarboxylic Acid