Compositional Changes in Atmospheric Deposition Driven by Recent Playa Exposures

Dry lakebeds in arid environments (playas) are globally important sources of particulate matter (PM). PM produced from playas, playa dust, is often dominated by evaporite minerals setting it apart from typical "mineral dusts" dominated by silicates and aluminosilicates. Here the influence of an expanding playa around the Salton Sea, CA, USA, on the composition of depositing PM is explored. Monitoring PM deposition allows continuous analysis of its composition over long temporal and wide spatial scales. Monthly deposition samples were collected at five sites in the Salton Sea Basin from May 2017-2018. Water extractable anion and total elemental concentrations of these samples were measured with ion chromatography (IC) and inductively coupled plasma mass spectroscopy (ICP-MS), respectively. These data were used to calculate elemental enrichment factors relative to the average crustal composition and as input values into positive matrix factorization (PMF) modeling. Initial results indicate that sites closest to playa surfaces have increased enrichments in Mg, Na, Ca, and Se. Interestingly, Na and Mg enrichments are not well correlated (R2=0.3), but enrichments of Mg and Ca are (R2=0.84). All three elements are thought to trace playa emissions, suggesting diverse compositions for emissive playas. These results confirm that playa emissions shift the composition of depositing dust away from the silicate end member towards evaporite salts and that the nature of this shift is dependent on playa composition. PMF results will be used to further isolate source profiles and estimate mass contributions of identified sources.