Supplemental Information

Mechanisms Leading to Oligomers and SOA through Aqueous Photooxidation: Insights from OH Radical Oxidation of Acetic Acid

Y. Tan1*, Y. B. Lim1, K. E. Altieri2, S. P. Seitzinger3, B. J. Turpin1** 1Department of Environmental Sciences, Rutgers University, 14 College Farm Road, New Brunswick, NJ 08901, USA 2Department of Geosciences, Princeton University, B80 Guyot Hall, Princeton, NJ 08544 3International Geosphere-Biosphere Programme (IGBP), Lilla Frescativägen 4a, Stockholm, Sweden *Current address: Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, 15213, Pennsylvania, USA **Corresponding author. Phone: (732) 932-9800 ext 6139; fax: (732) 932-8644; e-mail: [email protected]

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6

4

2 20 M acetic acid + OH 0

20 M)  15

10

5 100 M acetic acid + OH 0 Concentration (

120

90

60

30 1 mM acetic acid + OH 0 0 50 100 150 200 250 300 Time (min)

Fig. S1. Oxalic acid time profiles from batch acetic acid + OH radical experiments. The

10 mM experiment is not shown here because OH radical concentrations were lower and therefore the production rate is not comparable.

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Conductivity (S) 024 50 2x104 113 175 A 4 89 0 1x10 0 2x104 113 175 4 87 B 5 A 1x10 0 B 5 C 3.0x10 5 87 C 10 1.5x10 0.0 4x104 unknown 1 4 177 15 2x10 0

4 unknown 1 4x10 177 D 20 D 2x104 E 0

unknown 2 4 unknown 3 1x10 133

Time (min) Time E Abundance 3 177 25 F 5x10 0 2x104

4 175 unknown 2 30 1x10 0 2x104 119 unknown 3 4 175 35 1x10 0 4x104 89 F 40 2x104 0 0 100 200 300 - m/z

Fig. S2. IC-ESI-MS spectra of 1 mM pyruvic acid + UV experiment (180 min. reaction

time). Peaks are labeled below with the names of authentic standards that have the same

retention time. (A) and glycolate (acetic acid, m/z- 59; glycolic acid, m/z- 75), (B) formate (cannot be detected by ESI-MS), (C) pyruvate (pyruvic acid, m/z- 87), (D)

succinate (succinic acid, m/z- 117), (E) malonate (, m/z- 103), (F) oxalate

(oxalic acid, m/z- 89).

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Conductivity (S) 2000 01020 59 A 0 1500 1000 5 A 2000 B B 1500 95 C 1000 10 4 3x10 87 C 2x104 1x104 15 0 3 4.0x10 61 unknown 4 20 unknown 4 2.0x103 Ion Abundance Ion unknown 3

Time (min) Time 4000 97 unknown 3 25 F 119 G 2000 195

30 1.0x105 89 F 5.0x104 35 0.0 4.0x104 117 G 4 40 2.0x10 0.0 0 100 200- 300 m/z

Fig. S3. IC-ESI-MS spectra of 1 mM pyruvic acid + OH radical experiment (180 min.

reaction time). Peaks are labeled below with the names of authentic standards that have

the same retention time. (A) acetate and glycolate (acetic acid, m/z- 59; glycolic acid,

m/z- 75), (B) formate (cannot be detected by ESI-MS), (C) pyruvate (pyruvic acid, m/z-

87), (F) oxalate (oxalic acid, m/z- 89), (G) mesoxalate (mesoxalic acid, m/z- 117).

Unknown 4 is likely (m/z- 61), a contaminant.

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