عنوان

Speciation of iron in ambient aerosol and cloudwater

TLpq304365943

انگلیسی

Speciation of iron in ambient aerosol and cloudwater

[Thesis]

R. L. Siefert

M. R. Hoffmann

California Institute of Technology

1997

213

Ph.D.

California Institute of Technology

1997

Atmospheric iron (Fe) is thought to play an important role in cloudwater chemistry (e.g., S(IV) oxidation, oxidant production, etc.), and is also an important source of Fe to certain regions of the world's oceans where Fe is believed to be a rate-limiting nutrient for primary productivity. This thesis focuses on understanding the chemistry, speciation and abundance of Fe in cloudwater and aerosol in the troposphere, through observations of Fe speciation in the cloudwater and aerosol samples collected over the continental United States and the Arabian Sea. Different chemical species of atmospheric Fe were measured in aerosol and cloudwater samples to help assess the role of Fe in cloudwater chemistry. Chapter 2 presents a set of experiments which used ambient aerosol samples suspended in aqueous solution and then irradiated with uv-light to simulate cloudwater conditions. These experiments found Fe to be a critical component for the production of usd\rm H\sb2O\sb2.usd Chapter 3 discusses the development and application of a novel photochemical extraction method for the determination of photochemically-available Fe in ambient aerosol samples. Photochemically-available Fe ranged from <4 ng m to 308 ng m and accounted for 2.8% to 100% of the total Fe in aerosol samples collected in California and New York. Calculations based on the results of these experiments predicted that redox reactions of Fe in cloudwater could be an important in situ source of oxidants (OH, HOusd\rm\sb2\sp{\cdot}/O\sb2\sp{\cdot\sb-}).usd Chapter 4 presents results of several field studies which measured the redox states of Fe and other transition metals (Mn, Cu and Cr) in cloudwater. These measurements were then used in thermodynamic models which predicted Fe(III) to be either as Fe(III)-hydroxy species or Fe(III)-oxalate species. However, an unidentified strong chelating ligand with Fe(III) was also suggested by the thermodynamic model results. Chapter 5 presents results of a field study conducted on the Arabian Sea. Total atmospheric labile-Fe(II) ranged between <0.09 ng m to 7.5 ng m during the inter-monsoon period, and was consistently below the detection limit during the southwest-monsoon period. The labile-Fe(II) measured during the inter-monsoon period was predominantly found in the fine fraction of the aerosol. Principal component analysis revealed a significant source of Fe and Mn which was not associated with the main aeolian dust component.

Biological sciences

Earth sciences

Health and environmental sciences

iron

nutrients

Pure sciences

M. R. Hoffmann

R. L. Siefert

p

[Thesis]

276903

a

Y