Chapter 13
Appendix C: Supplementary Material for “Particle Phase Acidity and Oligomer Formation in Secondary Organic Aerosol”
*
* This chapter is reproduced by permission from supplementary material for “Particle phase acidity and oligomer formation in secondary organic aerosol” by S. Gao, N.L. Ng, M.D. Keywood, V. Varutbangkul, R. Bahreini, A. Nenes, J. He, K.Y. Yoo, J.L. Beauchamp, R.P. Hodyss, R.C. Flagan, J.H. Seinfeld, J. Phys Chem., 10.1021/jp047466e, 2004. Copyright 2004, American Chemical Society.
Figure C.1. The extracted ion chromatograms of 185, 171, 199 and 183 ions detected by the LC-MS in the SOA from the same α- pinene ozonolysis experiment as shown in Figures 9.2(a) and 9.3 (a). A Nova-Pak C18 column (300 × 3.9 mm, Waters) was used in the LC. 185 and 183 are identified as cis-pinic acid and cis-pinonic acid, respectively, by comparing with standard compounds. 171 and 199 are tentatively identified as norpinic acid and hydroxy pinonic acid, respectively, although isomers are likely present. The molecular structures of these four compounds are drawn alongside the corresponding ion chromatograms (only one isomer is drawn for the 199 ion).
2 4 6 8 10 12 14 16 18 min
0 100000 200000 300000 400000 500000
m / z = 185
min
2 4 6 8 10 12 14 16 18
0 50000 100000 150000
m / z = 171
min
2 4 6 8 10 12 14 16 18
0 25000 50000 75000 100000 125000
m / z = 199
min
2 4 6 8 10 12 14 16 18
0 10000 20000 30000 40000 50000
m / z = 183
HO O O
OH O HO O
OH
O OH OH O
O OH O
Figure C.2. Ion trap mass spectrum (- ion mode) of the extract of SOA from the same α-pinene ozonolysis experiment as shown in Figures 9.2(a) and 9.3(a). In all SOA samples from α-pinene ozonolysis, 185, 171 and 199 are detected as the most abundant low- MW species (after deprotonation), by both the IT-MS and LC-MS (see text). The identified (185) and tentatively identified (171, 199) structures are shown next to their corresponding ions. The 863.1 ion is from the instrument background. All other background ion intensities are lower than 1% of the maximum intensity (m/z = 185.0, designated as 100%). Consistent with the tandem mass spectra (MS/MS), the small oligomers with m/z of 329, 343, 357, 371, and 385 (after deprotonation) correspond to the possible combination of two norpinalic acids (MW = 156), norpinalic acid and norpinonic acid (170), two norpinonic acids, norpinonic acid and pinonic acid (MW = 184), pinonaldehyde (MW = 168) and hydroxy pinonic acid (MW = 200), respectively, through gem-diol reaction (see reference 13 for structures of these monomers). Combination of other monomers resulting from α-pinene ozonolysis is very likely, through the reactions proposed in the text.
200 300 400 500 600 700 800 900 1000 1100 1200
0 5 10 15 20 25 30 35 40 45
50 185.0
198.9
356.7 342.8 214.8
863.1 370.7
328.8 384.6 484.9 560.6 626.8 648.7 738.8 784.8 862.1 864.1 942.5 1030.8 1158.4
Relative abundance (%)
m/z 185: cis-pinic acid
171: norpinic acid
Small Oligomers m/z = 329, 343, 357, 371, 385 199: hydroxy pinonic acid
O HO O
OH HO O
O OH
O OH OH O
Figure C.3. Ion trap mass spectrum (+ ion mode) of the extract of a typical blank filter serving as the background MS. In the m/z range of 150 to 1600, most ion intensities are below 400000. The several exceptions, such as 268.9, 413.3, 514.8, 596.7, and 803.2 ions, are not among the most abundant ions in the IT-MS of SOA samples from α-pinene ozonolysis (e.g., see Figures 9.2, 9.4, and 9.5) or cycloalkene ozonolysis. Most likely, they come from either solvent or instrument background.
200 400 600 800 1000 1200 1400 1600
m/z
0 500000 100000 0 150000 0 200000 0 250000 0 300000 0 350000 0 400000 0 450000 0 500000 0 550000 0 600000 0 650000 0 700000 0 750000 0 800000 0 850000 0 900000 0 950000 0
268.9 413.3 514.8 596.7 803.2 842.7 678.8
350.8
186.9 978.5 1040.6 1266.0 1310.9 1490.9 1537.5
Intensity
Figure C.4. Ion trap mass spectra (+ ion mode) of the extracts of SOA from another pair of α-pinene (96 ppb) ozonolysis
experiments: (a) on MgSO4-only seed. (b) on MgSO4-H2SO4 seed. Other experimental conditions are identical.
200 400 600 800 1000 1200 1400 1600
m/z
0 500000 1000000 1500000 2000000 2500000 3000000 3500000 4000000 4500000 5000000 5500000 6000000 6500000 7000000 7500000 8000000
381.1
321.0
395.1 411.0
619.1 425.0
300.9
551.1 523.0
269.0 623.1
239.0 635.1
739.0
209.0 781.0 838.9
904.9 952.7 1227.
8 1326.
1077. 1
9 1550.
1 1447.
1
(a)
Intensity
200 400 600 800 1000 1200 1400 1600
m/z
0 500000 1000000 1500000 2000000 2500000 3000000 3500000 4000000 4500000 5000000 5500000 6000000 6500000 7000000 7500000
8000000 553.4
537.1 607.2 621.1 381.0
651.1
521.2 693.1
737.0 355.0
751.2 765.0 300.9
239.0
821.1 886.6
935.0 1072.
6
1194.
9 1246.
169.0 6 1387.
0 1573.
4 1438.
4
(b)
Intensity
Figure C.5. The likely structures of 313, 171 and 185 fragment ions in Figure 9.3(a). It is worth noting that our Figure 9.3(a) is similar to Figure 9 in Hoffmann et al., J. Geophys. Res., 103, 25,569 – 25,578 (1998), where they used atmospheric pressure chemical
ionization (APCI)-MS to analyze SOA samples from α-pinene ozonolysis. Besides the well-known inherent artifact with APCI technique of forming adducts and clusters during analysis, a fundamental difference is Hoffmann et al. interpreted the 357 ion as a molecular cluster formed through intermolecular forces (i.e., H-bonding) between acids, whereas we propose the 357 ion as a true dimer formed through covalent bonds via gem-diol reaction. Covalent bonding is much stronger than H-bonding, therefore making the formation and presence of the dimers in SOA, depicted in our Figure 9.3(a), more feasible.
HO O OH
O
O -
313
HO
O O -
171
OH
O
O - HO
185
Figure C.6. Ion trap mass spectrum (- ion mode) of the extract of SOA from the ozonolysis of 184ppb cycloheptene on dry (NH4)2SO4 seed. The background ion intensities are lower than 5% of the maximum intensity (m/z = 373.1, designated as 100%).
100 150 200 250 300 350 400 450 500 550 600 650 700
m/z
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
100 373.1
194.8
417.3
461.3 329.1
96.9
598.7 576.6 505.3
216.8 456.7 696.5
336.7 620.7
292.7 515.0
380.7
159.0 271.9 664.6
145.1 93.2
Relative abundance (%)
