Ebben et al. Page S1
Supporting Information for
Stereochemical Transfer to Atmospheric Aerosol Particles Accompanying the
Oxidation of Biogenic Volatile Organic Compounds
Carlena J. Ebben,1 Soeren R. Zorn,2 Seung-Bok Lee,2 Paulo Artaxo,3 Scot T. Martin,2*
Franz M. Geiger1*
1
Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL
60208, USA; 2School of Engineering and Applied Sciences & Department of Earth and
Planetary Sciences, Harvard University, 29 Oxford Street, Cambridge, MA 02138, USA;
3
Department of Physics, University of São Paolo, São Paolo, Brazil.
For the laboratory measurements of synthetic aerosol particles, stereoisomers of
-pinene were obtained from Aldrich. The lots contained an enantiomeric excess of 98%
for (+)--pinene and of 96% for (–)--pinene, with a chemical purity of 98.5% to 99.7%,
and were used as received. Pinene mixtures were prepared using a 100 µL syringe, and
the uncertainties in the stereoisomeric composition were estimated by error propagation
as ±5%.
As described in the main text, the pinene mixtures were exposed to ozone in the
Harvard Environmental Chamber. The chamber was operated as a continuous-flow tank
reactor. The particles grew to a geometric mean diameter of 93 nm with a geometric
standard deviation of 1.57 on ammonium sulfate seed particles that had an initial
geometric mean diameter of 50 nm with a geometric standard deviation of 1.23 during a
period of at least 24 hr at a temperature of 25.0 ± 0.1°C and 40 ± 1% relative humidity at
low NOx (< 1 ppb). The organic particle mass concentration was 16 µg m-3. Particles
were collected at a sampling flow of 6 sLpm for 48 hr on Teflon filters from the
continuous outflow of the chamber (Sartorius, PTFE, part # 11807-47-N, 200 nm pore
size). For the sampling conditions, upper limits of the total mass deposited on the filters
were 285 µg for the 98:2 mixture of (+):(–)--pinene, 397 µg for the 74.5:25.5 mixture,
and 432 µg for the 51:49 mixture. Other filter samples were also collected and analyzed,
and the indicated masses are restricted to the presented data of Fig. 2. When necessary for
control samples, particles were removed prior to sampling by the use of a HEPA filter
(Pall HEPA capsule, part #12144).
The field station was located at tower TT34 at a remote site in the central Amazon
Basin located at S 02º 35.675', W 060º 12.557' (Martin et al., 2010). A micro-orifice
uniform-deposit impactor (MOUDI) (Marple et al., 1991) loaded with Whatman
Nucleopore filters having 0.4 µm pore size was used to collect size-resolved particle
samples. The particles represented by Fig. 3 were collected one month after the
conclusion of AMAZE-08 from 09 April 2008 to 17 April 2008.
For SFG-LD analysis, the filter samples were placed under a fused silica window.
A broadband 120 fsec infrared optical parametric amplifier running at a 1 kHz repetition
rate was used. Each spectrum was obtained by upconverting the infrared light field using
a visible pump beam from a regenerative amplifier that was filtered with two narrow
band-pass filters (F1.1-800.0-UNBLK-1.00, CVI) to provide an 800-nm pump pulse with
a bandwidth of 1.57 nm. The spectra were recorded in triplicate using the p+45p and the
p-45p polarization combination in random sequence. The spectra were recorded using a
2
hybrid scanning/broadband method to ensure that each vibrational mode was accessed
with the same incident infrared power. The incident pulse energies were limited to 10-6 J,
and the focal points of the infrared and the visible laser beams were 30 to 50 µm. For a
filter having 500 μg of organic material, there was approximately 10-9 g of organic
material in the area sampled by the laser spot.
The SFG-LD spectra were analyzed using the procedures described in (Oh-e et
al., 2004; Stokes et al., 2007), which include referencing the spectra to the SFG response
from a gold substrate to account for the energy distribution in the infrared for each
polarization combination and normalization to input power. For a given spectral pair, the
SFG difference spectrum was obtained by taking the difference between the p-45p and
the p+45p spectrum. Slight variations in signal yields obtained during each trial were
accounted for in each spectrum shown in Fig. 2A by representing the average of three
SFG difference spectra that were obtained after normalizing the spectra to the same noise
level in the 3100-3200 cm-1 region. This frequency range was chosen to represent the
noise because vibrational modes were not observed in it. To take into account that chiral
SFG signal intensities scale with the square of the number of oscillators in a given bulk
sample and that this quantity is proportional to the mass of the sample, we divided the
intensity values of each data pair by the square of the relative mass difference between
each filter relative to the one containing the least material (i.e., 285 µg for the particle
phase prepared from the 98:2 mixture of (+):(–)--pinene). The resulting scaling factors
were 1.52, 1.39, and 1.00 for the integrated intensities at 8, 49, and 96% ee, respectively.
As shown in Fig. S2, the unscaled data result in the same nonlinear relationship.
3
References
Marple, V. A., K. L. Rubow, and S. M. Behm (1991), A Microorifice Uniform Deposit
Impactor (MOUDI) - Description, Calibration, and Use, Aerosol Sci. Technol., 14(4),
434-446.
Martin, S. T., M. O. Andreae, D. Althausen, P. Artaxo, H. Baars, S. Borrmann, Q. Chen,
D. K. Farmer, A. Guenther, S. S. Gunthe, J. L. Jimenez, T. Karl, K. Longo, A. Manzi, T.
Pauliquevis, M. D. Petters, A. J. Prenni, U. Poschl, L. V. Rizzo, J. Schneider, J. N. Smith,
E. Swietlicki, J. Tota, J. Wang, A. Wiedensohler and S. R. Zorn. An Overview of the
Amazonian Aerosol Characterization Experiment 2008 (AMAZE-08). Atmos. Chem.
Phys. 10: 11415-11438, 2010.
Oh-e, M., H. Yokoyama, S. Yorozuya, K. Akagi, M. A. Belkin and Y. R. Shen. Sumfrequency vibrational spectroscopy of a helically structured conjugated polymer. Phys.
Rev. Lett. 93: 26, 2004.
Stokes, G. Y., F. C. Boman, J. M. Gibbs-Davis, B. R. Stepp, A. Condie, S. T. Nguyen
and F. M. Geiger. Making ‘Sense’ of DNA. J. Am. Chem. Soc. 129: 7492-7493, 2007.
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SFG Difference
80
60
40
20
0
3200 3100 3000 2900 2800 2700
-1
Infrared Energy (cm )
Fig. S1. SFG-LD spectrum of a fused silica window exposed to the equilibrium vapor
pressure of (+)--pinene at 290 K and 1 atm of air.
5
400
200
0
-1
0
100
EE(+)--pinene
•SFG, 3000-2900 cm
600
Fig. S2. Total SFG-LD response between 2900 and 3000 cm-1 without scaling for total
particle mass on the filters. The response is shown as a function of enantiomeric excess of
(+)--pinene in the gas phase during aerosol formation, with the background SFG-LD
response from a Teflon filter (no particle phase present) indicated by the horizontal
dashed line.
6