Date of Award
Chemistry and Biochemistry
Brian J. Majestic
The processes by which iron is solubilized are largely unknown. There are three hypotheses on how iron is soluble: 1) iron is thought to undergo an acid based solubilization process, 2) iron undergoes an oxidation/reduction process and reduces iron(III) to the more soluble iron(II), and 3) iron is bound to organic molecules, which solubilizes it. The 3 hypotheses on iron water-solubilized are explored by presenting two individual studies.
The first study investigates iron directly from car exhaust. Exhaust particles were collected from 32 vehicles. Iron solubility in these samples ranged from 0%-82% with the average iron solubility being 30%. X-ray absorption near edge structure (XANES) spectroscopy showed that Fe(III) was the primary oxidation state of iron. Water-soluble iron was not correlated to sulfates, which are frequently found in aerosols as an acidic species. Last, correlation of iron was explored with respect to intermediate volatility organic compounds (IVOCs) and naphthalene and resulting R2 as high as 0.56. A bench top study verified the results by showing an increasing water-solubility iron by a factor of 5.5. Thus, a hypothesis was developed that, during the extraction process, the organic components of the PM become oxidized and chelate the iron into water.
The observation from the car exhaust led to the investigation of PM and iron in the ambient atmosphere known as the Platte River Air Pollution and Photochemistry Experiment (PRAPPE). The samples from PRAPPE were collected for a 24-hour period during summer (August 2017) and winter (December 2016 - March 2017). Here we compared PM2.5 from 3 different sites including Denver (an urban), Jackson Lake State Park (a rural), and Platteville (a mixed site). The speciation of the iron component of the PM was also investigated. It was found the almandine (Fe₃Al₂Si₃O₁₂) was the most abundant iron complex follow by magnetite (Fe3O4) then Fe(III)dextran. Last, no correlation to iron oxidation and iron solubility was found.
The two studies showed that water-soluble iron is not correlated to sulfates. Iron oxidation state was not a factor in the resulting water-soluble Iron. Iron water-solubility was a result of iron organic interaction.
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Salazar, Joseph R., "Iron in Urban Air Pollution" (2020). Electronic Theses and Dissertations. 1836.
Received from ProQuest
Joseph R. Salazar