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 - #30488Whole 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 METHODSWhole 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.

2 4 6 8 10 12 14 16 18 20 220

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[DMS] (pptv)

[Eth

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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

• aerosol mass• Central Valley was seen to have an average

submicron particle count of 4 µg/m3

• 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.