Understanding the sources and atmospheric processes of soluble iron in aerosols using a synergistic measurement approach

The theme of this thesis is the characterization of soluble iron in atmospheric aerosols through the use of online and offline measurements. Using this synergistic measurement approach, a comprehensive perspective of chemical and physical properties of soluble iron aerosols was acquired. This unique dataset provided valuable insight into the major sources and atmospheric processes contributing to the presence of soluble iron aerosols in the atmosphere.;As a part of this thesis, a new measurement method was developed resulting in the first semi-continuous measurements of water-soluble ferrous iron (WS_Fe(II)) in aerosols. The prototype consisted of an online particle collection device (Particle-Into-Liquid-Sampler (PILS)), coupled to a liquid waveguide capillary cell (LWCC) and a portable spectrophotometer for WS_Fe(II) detection by the ferrozine technique. The combined method, known as the PILS-LWCC, yielded highly time-resolved WS_Fe(II) measurements in atmospheric aerosols (12-minute measurement), with a method limit of detection of 4.6 ng m-3 and a measurement uncertainty of 12%.;Following instrument development, the PILS-LWCC was deployed at two urban sites (Dearborn, MI and Atlanta, GA) with contrasting emissions during different seasons, and at a rural site (Southeastern US) during a biomass burning event to characterize WS_Fe(II) sources and temporal variability. During field deployment, no clear diurnal trends in WS_Fe(II) were observed at any urban site studied. The lack of a day-time increase in WS_Fe(II), suggested that photoreductive processes only play a minor role in WS_Fe(II) variability. High temporal variability, however, was observed at all urban sites, where concentrations often changed from the method limit of detection (4.6 ng m-3) to approximately 300 to 400 ng m-3, lasting only a few hours (e.g. WS_Fe(II) transient events). Several transient events observed in Atlanta, GA and Dearborn, MI predominately occurred during times of low wind speeds and appeared to be from local industrial sources or processes. Other transient events observed exclusively in Atlanta were associated with sulfate plumes. The highest WS_Fe(II) concentrations in these event plumes corresponded to apparent aerosol acidity (based on the concentrations of major inorganic ions).;To understand how other physical and chemical properties affect iron solubility in ambient aerosols, advanced synchrotron-based methods were used, specifically X-ray Absorption Near Edge Structure (XANES) spectroscopy and micro X-ray fluorescence techniques. These techniques are capable of determining detailed chemical speciation (e.g. oxidation state and chemical composition) and mixing state (e.g. elemental associations) in single particles. The first synchrotron study focused on detailed characterization of chemical speciation in fine iron-containing particles deposited on a variety of ambient urban (Atlanta, GA) and rural (Fort Yargo, GA) Teflon filter samples. This unique data was used in conjunction with iron solubility measurements (soluble iron/total iron) to evaluate the importance of speciation as a control factor of iron solubility.;Similar analyses were performed on single iron-containing particles from source emission fine particles (e.g. biomass burning, coal fly ash, mineral dust, and mobile) to continue investigating the relationship between speciation and iron solubility. Major differences were observed in iron solubility in source emission particles, ranging from very low solubility (<1%, mineral dust, coal fly ash) to 75% (diesel exhaust, gasoline exhaust, biomass burning smoke). Similar to the findings in ambient aerosols, differences in iron solubility did not correspond to changes in oxidation state and/or the abundance of major iron phases (iron oxides vs. iron silicates) based on XANES and micro X-ray fluorescence single particle analysis. Single particle sulfur content, however, corresponded to iron solubility. Similar trends between single particle sulfur content and soluble iron were also observed in a winter and summer sample collected in Atlanta, GA (South Dekalb site). (Abstract shortened by UMI.)...