Characterizing Great Salt Lake Dust Relative other regional Dust Sources.
Faculty Mentor: Greg, Carling, Geological Sciences
Dust storms occur frequently along the Wasatch Front. These dust events may have negative effects on human health and agriculture. To help understand dust events along the Wasatch Front, this study focuses on analyzing dust deposition to better locate dust emission sources. Understanding the source of dust events is important. This is important because Great Salt Lake water levels are dropping exposing lakebed. This newly expose lakebed may result in increased frequency and intensity of dust events. To understand if this lakebed is affecting the Wasatch Front and acting as an emission source.
Four sampling locations were chosen to distinguish dust emitting from Great Salt Lake lakebed and other regional dust sources. These sampling locations are Provo, Salt Lake City, Ogden, and Logan. Sampling was done by placing passive dust samplers on roofs of university buildings in each location. Before placing each sampler, sampling containers were acid washed for 24 hours and placed in clean bags. The passive samplers were place during Fall 2015. Upon retrieval of the samplers, they were washed with ultrapure water into clean 2-liter bottles for transport. Samples were dried in a laminar flow hood, and weighed.
To prepare samples for ICP-MS, the samples were boiled with 30% hydrogen peroxide till CO2 emissions ceased. This indicated that all organic matter dissolved and evaporated. Next, the samples were sequentially leached using an ammonium acetate pH7 buffer, acetic acid, nitric acid and aqua regia. After each leaching step, leachate was separated then dust was washed with ultrapure water with ammonium pH7 buffer, centrifuged, and decanted. Each sequential leach was 24 hours, except aqua regia which was 72 hours. Samples were then analyzed for trace elements with ICP-MS.
To better understand differences between the samples, the enrichment factor for element in the sample was calculated. This was done by the following formula:
Where EF is enrichment factor, X is referring to the element being calculated, and UCC is the upper continental crust(UCC) from Rudnick et al (2003).
A graph of the ammonium acetate leachate enrichment factor is plotted in figure 1. This graph shows similarities and differences between sample locations. There is elevated concentrations of Na, Ca, K, Mg and Li in the Logan, Ogden and Salt Lake sites. These elevated levels of salts are consistent with expected results. These results show that Great Salt Lake dust, which is elevated in salts, is contributing to these areas.
The Salt Lake sample is elevated in Pb, La, Nd, As and Zn. Further study is needed to understand sources the enrichments. Likely cause of enrichment is anthropogenic so elements will be ignored for distinguishing potential sources.
The high levels of La and other rare earth elements are known to negatively affect agriculture (Zhang et al, 2015). High levels of La and Pb are likely related to petroleum refining (Bozlaker et al, 2013). These high levels of La and Pb are likely related to the oil refinery in the Salt Lake area. Further study is needed to understand the impact of these rare earth elements on the Salt Lake area.
There are some issues with the nature of the project. Only dust depositional samples were able to be analyzed. Further work is needed to sample emission sights and correlate them with the characteristics of the depositional sights. Understanding this relationship will help to better understand impacts from Great Salt Lake dust relative to other dust sources.
In addition to better understanding Great Salt Lake dust relative to other regional dust source. This study also helped to better understand how to differentiate samples based on trace element signatures. This study used a four step sequential leach to analyze each sample. The first step of the sequential leaches was ammonium acetate at pH 7. The ammonium acetate best represented distinguishing characteristics among the four samples. This method of analysis differs from other studies which do a complete digestion with hydrofluoric acid. Future work with differentiating sample sites based on trace element patterns will have better results if the ammonium acetate leachate is used.
In conclusion, Great Salt Lake dust is likely a contributor to dust emissions in the Salt Lake, Ogden and Logan areas. However, further study is needed to sample and analyze dust emission sources in Utah. These samples will be key to chemically linking source to sink for dust characteristics and trajectories.
Bozlaker, Ayse, Joseph M. Prospero, Matthew P. Fraser, and Shankararaman Chellam. “Quantifying the Contribution of Long-Range Saharan Dust Transport on Particulate Matter Concentrations in Houston, Texas, Using Detailed Elemental Analysis.”Environmental Science & Technology Environ. Sci. Technol. (2013): 130909083424001. Web.
Rudnick, R.l., and S. Gao. “Composition of the Continental Crust.” Treatise on Geochemistry (2003): 1-64. Web.
Zhang, Xuanbo, Yuping Du, Lihong Wang, Qing Zhou, Xiaohua Huang, and Zhaoguo Sun. “Combined Effects of Lanthanum (III) and Acid Rain on Antioxidant Enzyme System in Soybean Roots.” PLOS ONE PLoS ONE 10.7 (2015): n. pag. Web.