Supporting Information for:
Anthropogenic Sulfur Perturbations on Biogenic
Oxidation: SO2 Additions Impact Gas-Phase OH
Oxidation Products of α- and β-Pinene
Beth Friedmanǂ, Patrick Brophyǂ, William H. Bruneǁ, Delphine K. Farmer*ǂ
ǂDepartment of Chemistry, Colorado State University, Fort Collins, CO, USA 80523-1872
ǁDepartment of Meteorology, Pennsylvania State University, University Park, PA, USA 16802
This Supporting Information includes 8 pages and 6 figures.
Sulfur-containing Organic molecules. The CxHyOzS- ion had the strongest signal, while
C2H3O5S-, was most strongly detected for α-pinene oxidation, with much lower signals in βpinene oxidation experiments, although this α-pinene enhancement is not consistently observed
for other CxHyOzS- (Figure 6b). An increase in RH leads to a decrease in the C5H4O5S- signal in
both the α- and β-pinene experiments, consistent with SO3+organic chemistry. However, an
increase in chamber RH increases the signals of C2H3O5S-, C10H16O5S-, and C3H3O6S- for both αand β-pinene experiments, inconsistent with SO3+organic chemistry. This suggests that water
inhibits formation of this organosulfur, possibly by quenching SO3. We note that while all of the
CxHyOzS- are negligible for the β-pinene oxidation, doubling the β-pinene concentration leads to
an increase in yields, most obviously C2H3O5S-. While the detection of these molecules may be
somewhat attributable to instrumentation artifacts and clustering in the system, we stress that
these molecules are detected differently in α- and β-pinene experiments, and these respective
trends may be further reflective of the differences between the two monoterpene isomers seen
throughout this study. Based on the timeseries and time to reach steady state of these sulfurcontaining organic molecules relative to pinonaldehyde, the net production rate of the sulfurcontaining organic molecules is fast, potentially the result of reactions between early generation
oxidation products.
Estimating Volatility of the Gas-Phase Species. Using the SIMPOL model,1 and following
assumptions outlined in previous work,2 volatilities were estimated for each carbon-containing
molecule detected by the CIMS in order to extend the CIMS data to potential SOA formation and
growth. Shown in Figure S4, the α-pinene and β-pinene data have a similar range of volatilities
that indicate simultaneous fragmentation and functionalization with added SO2. The plots shown
S1
in Figure S4 have the same conditions as the mass defect enhancement plots shown in Figure 2
(only including species with a signal to noise of at least 3, only carbon-containing molecules,
only species that changed by more than 10% relative to no SO2 added). Added ranges of known
VOC volatilities3 indicate that the majority of observable species sit in intermediate and semivolatile range, although there is a range of estimated volatilities that change with added SO2.
Impact of Ozonolysis. An ozonolysis experiment with alpha-pinene was conducted, at the same
ozone levels as measured in the OH oxidation experiments. Flows through the PAM chamber
were also replicated. No products were observed from the α-pinene + O3 reaction. Added SO2
(58 ppb) did not produce any measurable CxHyOzS species. Measurable oxidation species were
only observed when the UV lights were turned on, indicative that the majority of observable
species are due to OH oxidation in the PAM chamber. Further, ozonolysis products were only
observed when the flow rate was decreased in the PAM chamber to allow a longer residence
time. We conclude from the ozonolysis experiment that with the conditions (flows, O3, H2O, and
BVOC concentrations) set as in the OH oxidation experiments, ozonolysis has a negligible
impact.
The timeseries (Figure S5) shows the lack of observable products from the ozonolysis
experiment until the UV lights are turned on, indicating that all observable products are from OH
oxidation, and the residence time and conditions in the PAM chamber are not sufficient for the
ozonolysis reactions to compete with OH oxidation. Mass defect enhancement plots are shown
in Figure S6, further verifying that OH was the dominant oxidant in the experiments presented.
S2
Figure S1. Top plot: Normalized formic acid signal as a function of added SO2 concentration
and RH. Lower plot: pinonic acid to pinic acid ratios as a function of added SO2 concentration
for both BVOC systems.
S3
Figure S2. Timeseries of relevant sulfur-containing species.
S4
Figure S3. Linear regression slopes of scatterplots as shown in Figure 6 made for the strongest
sulfur-containing organic molecules detected against ISO2- for each experiment.
S5
Figure S4. Estimated volatilities for each carbon-containing molecule detected by the CIMS.
Representative α- and β-pinene oxidation experiments with two different SO2 concentrations are
shown. Only including species with a signal to noise of at least 3 that changed by more than 10%
relative to the no SO2 experiment. Added ranges of known VOC volatilities are indicated by the
shaded regions.3
S6
Figure S5. Normalized timeseries of relevant species in the ozonolysis experiment. Top panel:
formic acid, ISO2-, ISO3-. Middle panel: pinonic acid and pinic acid. Lower panel: sulfurcontaining organic species detected in the OH oxidation experiments.
indicate experimental conditions.
S7
Vertical solid lines
Figure S6. Mass defect enhancement plots of the ozonolysis experiment. Only species with a
change of at least 10% and a signal to noise ratio of at least 3 are shown (as in Figure 2). Left: αpinene + 400 ppb ozone. Middle: α-pinene + 400 ppb ozone + 58 ppb SO2; right: α-pinene + 400
ppb ozone + 58 ppb SO2+lights. Minimal changes were observed until the lights were turned on.
References
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Pankow, J. F.; Asher, W. E, SIMPOL.1: a simple group contribution method for
predicting vapor pressures and enthalpies of vaporization of multifunctional organic compounds.
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chemical ionization mass spectrometry measurements to estimate volatility distributions of apinene and naphthalene oxidation products. Atmos. Meas. Tech. 2015, 8, 1-18.
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S8