Iron is the most abundant transition metal in atmospheric particulate matter and plays a crucial role in atmospheric sulfur and carbon cycles. The role of iron in these cycles depends on iron solubility, and thus its speciation, both of which are altered as iron is transformed from atmospheric emission to deposition. Extensive work has focused on iron behavior in atmospheric environments. However this work has not controlled for particle size. As atmospheric iron is present in sizes ranging from a few nanometers up to tens of microns, studies of how particle size influences atmospheric iron chemistry and iron solubility are needed. Intellectual Merit: This project will examine the influence of particle size on atmospheric reactions of iron and, in turn, the influence of particle size on iron solubility. In particular, we will investigate how particle size affects iron solubility during atmospheric processing by two different mechanisms. First, the effect of particle size on iron solubility during photoreduction of Fe(III) in cloud waters will be determined. Photochemical reduction of aqueous Fe(III) has been well studied in authentic and simulated cloud waters. Particle size has never been considered as a variable, but may be important because only a restricted aerosol size fraction can form cloud condensation nuclei (CCN). Although the photochemical reduction of Fe(III) takes place in the aqueous phase, particle size may play an integral role. As particle size decreases (and surface area increases), a greater fraction of the iron will be available for dissolution. We hypothesize that the increased iron solubility will result in more iron available for photochemistry. Previous laboratory studies focusing on particles too big or too small to act as CCN may under- or overestimate the soluble iron resulting from photochemistry in real atmospheric systems. In this study, we will measure the extent that particle size plays a role in iron solubility and subsequent photoreduction. Second, we will investigate the influence of particle size on iron solubility during reaction with gaseous SO2. Exposure of iron phases mixed with NaCl will be studied at two relative humidities (20% and 80%), representative of dry continental and wet marine environments. This will allow us to determine if gas-particle or liquid-particle reactions are more important during Fe-S interactions. Following exposure to SO2, iron isotope composition of the dissolved iron fraction will be used to elucidate mechanisms. Detailed mechanistic data will be obtained using EXAFS spectroscopy pre- and post- SO2 exposure.
|Effective start/end date||5/1/10 → 4/30/14|
- National Science Foundation (NSF): $220,238.00
cloud condensation nucleus