Title

The chemical characteristics of marine mineral aerosol solutions at ambient relative humidities and some effects on iron chemistry

Date of Award

1992

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Marine and Atmospheric Chemistry

First Committee Member

Joseph M. Prospero, Committee Chair

Abstract

It has been suggested that iron could play a critical role as a limiting micronutrient in some ocean regions where the concentration of major nutrients is high but primary productively is low. Because aerosol iron is the predominant pathway to supply iron to the open oceans, this dissertation focuses on the factors that affect the iron solubility in aerosol particles before they enter the oceans. The major thrust is the study of the mechanisms of the interactions between aerosol iron and marine aerosol solutions while the particles are suspended in the marine atmosphere.Iron solubilities in marine aerosol solutions were estimated at the pH and ionic strength that are characteristic of ambient trade wind aerosol particles collected at Barbados. Under typical marine conditions, aerosol solutions could have very high ionic strength and extremely low pH even when part of the acid has been neutralized by NH$\sb3$ and CaCO$\sb3$. The iron solubility in aerosol solutions is far higher than that normally expected for seawater and even rainwater. Thus aerosol solution processes may be the major factor that determines how much iron will readily dissolve when particles enter the ocean.Iron photochemical and speciation studies indicated that only about 1% of the total Fe and 7.5% of the soluble Fe in Barbados mineral aerosols was in the Fe(II) form. Although the presence of organic ligands such as oxalate can greatly increase the Fe(II) concentration during photolysis, Fe(II) levels dropped rapidly in the dark due to the oxidation of Fe(II) with H$\sb2$O$\sb2$ that is also produced during irradiation. Geothite solubility studies suggested that photochemical processes affect only the soluble iron species and have no significant impact on the total iron solubility.These results suggest that marine aerosol solutions are characterized by extreme conditions that can greatly affect the chemical processes that occur in the aerosol phase. As a result, the mobilization of iron and its subsequent fate in natural waters will be strongly dependent on the past history of the aerosol particles in the atmosphere.

Keywords

Physical Oceanography; Physics, Atmospheric Science

Link to Full Text

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