10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Origin of Soluble Iron from Low-emitting Automobile Exhaust
JOSEPH SALAZAR, Benton Cartledge, Lynn Russell, Allen Robinson, Greg Drozd, Allen H. Goldstein, Brian Majestic, University of Denver
Abstract Number: 1161 Working Group: Combustion-Generated Aerosols: the Desirable and Undesirable
Abstract Soluble iron has been found to be a limiting reagent for phytoplankton in most of the southern oceans. Phytoplankton is a vital part of the ocean's ecosystem as it is involved in CO2 uptake and nitrogen fixing. Thus, understanding iron geochemical cycle is essential to understanding the earth’s oceans and atmospheric interactions. Soluble iron has been correlated to oxalates, nitrates and sulfates resulting in the hypothesis that iron is solubilized through an acid processing mechanism. Despite the correlations in field studies, these relationships have not been reliably proven in the laboratory. Previous field studies have linked soluble iron over the ocean to combustion sources and, in general, relative soluble iron tends to be greater in urban areas. To understand the origin of soluble iron in urban areas, PM was collected from the tail pipes of low emitting gasoline vehicles at the CARB dynamometer facility using the California Unified (UC) Drive Cycle. The PM was collected from the exhaust pipe and analyzed for inorganic ions, EC/OC, total and soluble metals, functional groups, and GC-MS was used to quantify the class of 11 to 18 carbon intermediate volatility organic compound (IVOC), ultimately categorized as alkane (ALK), single ring aromatic (SRA) and general (GEN) for each number of carbon. The results showed that the tested automobile emissions have a high fraction of percent iron solubility ranging from 0% - 81.9% with an average of 26.7%. This is a significant increase compared to crustal sources where the soluble iron is approximately 1% of total iron. The samples were analyzed by x-ray near edge absorption structure (XANES) spectroscopy, which confirmed that only Fe(III) was present in the samples and, thus, any increased solubility was not due to the presence of the more soluble Fe(II). Correlation of soluble iron to sulfate was insignificant (R2 = 0.157), as was the correlation to every measured chemical component, except one class. Soluble iron was highly correlated to the C11 - C18 IVOCs, with R2 values as high as .981 for IVOC SRA-C14. These results imply that the large driver in soluble iron from gasoline vehicle emissions is related to the organic fraction of the PM, suggesting that further studies are required to study metal-organic interactions in PM.