- Air samples taken over the Salton Sea in 2014 found higher concentrations of dimethyl sulfide (DMS) over neighboring agricultural land than over the sea, even though both are known to be emitted by marine environments. - Further analysis showed DMS concentrations were correlated with ethanol, indicating dairy emissions as the source of DMS rather than transport from the Pacific Ocean. - Samples across the California Central Valley from 2009-2014 found an average DMS concentration of 27.2 pptv, suggesting local agricultural sources contribute to DMS levels. - Preliminary calculations estimate DMS may account for at least 1.1% of aerosol loadings in the Central Valley through its role in particle formation.

1. CONCLUSIONS:
Elevated DMS concentrations were seen over the land
around the Salton Sea, although methyl iodide
concentrations were lower over the sea itself. It was
hypothesized that DMS was being emitted from
terrestrial sources, so DMS concentrations were
analyzed in the Central Valley. Especially high
concentrations were found in the Central Valley,
especially in the northern section of the sampled region.
A preliminary estimate suggests that DMS may be
contributing at to at least 1.1% of the aerosol loadings in
this region. This estimate needs to be reevaluated,
however, as it is possible that the value is too low
because other the aerosol particles could be acting as
nuclei for the growth of larger aerosols.
Figure 1: Dimethyl Sulfide and Methyl Iodide Concentrations
Around the Salton Sea
Dimethyl Sulfide Emissions from Dairies and Agriculture as a Potential
Contributor to Sulfate Aerosols in the California Central Valley
Eric D. Lebel1, Josette E. Marrero2, Timothy H. Bertram3, and Donald R. Blake2
1Department of Chemistry and Biochemistry, Providence College, Providence, RI 02918
2Department of Chemistry, University of California Irvine, Irvine, CA 92697
3Department of Chemistry, University of Wisconsin Madison, Madison, WI 53706
Figure 2: HYSPLIT Models Show the Possible Sources for the Air
Around the Salton Sea
Figure 3: Ethanol vs. DMS Concentrations Around the Salton Sea
Figure 1: Air samples were taken on June 23, 2014 at altitudes below 2,000 ft and
analyzed for dimethyl sulfide (DMS) and methyl iodide concentrations. Both gases are
known to be emitted from marine environments, but interestingly, DMS is present in
higher concentrations over the land, while methyl iodide concentrations are generally
higher over the sea. The average concentration of DMS over the land is 14.0 pptv.
Figure 2: HYSPLIT models
suggest that the Pacific
Ocean could be source of
the air around the Salton
Sea, but because of the
significant amount of time
that it took for the air to
travel between the Pacific
Ocean and Salton Sea, it is
unlikely that the DMS
originated in the ocean.
ABSTRACT - #30488
Whole air samples have been collected
throughout Southern California during the
previous five years of the NASA Student
Airborne Research Program (SARP). During a
flight over the Salton Sea in 2014, higher
concentrations of dimethyl sulfide (DMS), a
known marine emitted gas, were observed over
neighboring agricultural land than over the sea
itself. A comparison of DMS to methyl iodide,
another known marine emitted gas, showed
minimal correlation, revealing that DMS was
being emitted from local sources. Ground
samples at the Salton Sea verified that the DMS
was not transported from the Pacific Ocean.
Previous SARP studies have shown that DMS is
emitted from dairies. The enhancements in
ethanol (another dairy tracer) and DMS in
several airborne samples collected south of the
Salton Sea suggest dairy emissions of the
observed DMS. DMS is a compound of interest
because its oxidation can form cloud
condensation nuclei. Based on data from all six
SARP flights between 2009-2014, we propose
that dairy and farming emissions of DMS in the
San Joaquin Valley may be impacting aerosol
loading in this region. Taking into account the
particulate matter mass loadings, a simple
calculation was used to determine the percent
contribution of DMS to aerosol formation for the
San Joaquin Valley.
ACKNOWLEDGEMENTS:
I would like to thank Don Blake, Josette Marrero, and Tim Bertram for
their assistance with this project. I would also like to thank the entire staff
of the National Suborbital Education and Research Center and NASA for
sponsoring the Student Airborne Research Program and for giving me the
opportunity to become introduced to atmospheric chemistry this past
summer.
Figure 3: Plotting the ethanol vs.
DMS concentration in the
agricultural regions around the
Salton Sea shows a possible
correlation between DMS and
dairies. Both DMS and ethanol
are known to be emitted from
dairies, so a correlation would be
expected if the source of DMS
was the dairies. However, there
are four points (blue squares) that
have a high DMS concentration,
but low ethanol concentration.
Figure 4: DMS Concentrations in the California
Central Valley, Excluding Dairies
Figure 4: A boundary (yellow line) that attempted to exclude
dairies (small red dots) at a distance of 5 miles was created.
Samples that were taken on June 24-25, 2014 below 2,000 ft.
and fell within this boundary were plotted and analyzed for
DMS concentrations. The average concentration is 12.9 pptv,
which is above the standard background concentration. Locally
higher amounts were observed, especially in the northern
regions of the boundary, with some individual measurements
approaching 80 pptv.
Figure 5: DMS concentrations in samples below 2,000 ft. in the
California Central Valley were plotted from all SARP campaigns
from 2009-2014. The average concentration of DMS was 27.2
pptv. There are locally higher concentrations, especially in the
northern region of the Central Valley, with some individual
samples showing DMS concentrations well above 200 pptv. This
suggests that local sources, such as agriculture, could be a
potential contributor to DMS concentrations in the Central Valley.
Figure 5: DMS Concentrations in the Entire
Central Valley from all SARP Years, 2009-2014
MATERIALS AND METHODS
Whole air samples were collected on the
research flights that were part of the Student
Airborne Research Program (SARP). In 2014,
over 300 samples were collected on flights taken
between June 23-25. All samples were collected
at a pressure of 40 psi into evacuated 2-Liter
electropolished stainless-steel canisters. The
sampling interval was between 25 seconds to 1
minute. The samples were then returned to the
Rowland-Blake Laboratory at the University of
California Irvine for gas chromatographic (GC)
analysis. Within 1 week, the samples were
analyzed for carbon monoxide (CO), carbon
dioxide (CO2), methane (CH4), and over 70 C2–
C10 VOCs, including hydrocarbons, halocarbons,
alkyl nitrates, oxygenates, and sulfur containing
compounds. The GC system utilizes three GC
units, six columns and detectors, including two
FIDs, two ECDs and a MS detector. Samples
were quantified by comparison to whole air
standards of known concentrations.
Figure 6: Calculations Suggest that DMS
Contributes to the Aerosol Loadings in the
Central Valley
Figure 6: Preliminary calculations suggest that
DMS may be contributing to at least 1.1% of the
aerosol loadings in the central valley. This value
may not be negligible because water and other
substances are able to add to the aerosol particles,
thereby increasing their mass.0
1000
2000
3000
4000
5000
6000
0 5 10 15 20 25
[Ethanol](pptv)
[DMS] (pptv)
Methyl Iodide
Concentrations
Dimethyl Sulfide
Concentrations
• 27.2 pptv average DMS from all SARP years
• 27.2 pptv = 0.074 µg/m3 for DMS
• 61.1% of DMS mass is converted to sulfate
aerosols in the absence of isoprene1
• 0.074
µ𝑔
𝑚3 × 0.611 = 0.045
µ𝑔
𝑚3 aerosol mass
• Central Valley was seen to have an average
submicron particle count of 4 µg/m3
•
0.045 µg/m3
4 µg/m3 = 𝟏. 𝟏% contribution of DMS to
aerosol loadings
1Chen, T.; Myoseon, J. Secondary organic aerosol formation from photooxidation of a mixture of dimethyl sulfide and isoprene. Atmospheric Environment. 2012. 46, 271-278.