Daniel W. O'Sullivan
Daniel W. O'Sullivan,
Professor and Chair
Ph.D., University of Rhode Island
U.S. Naval Academy
572M Holloway Road
Annapolis, MD 21402-5026
Development of novel analytical methods and design of innovative sampling systems for the evaluation of photochemical and redox reactions in natural waters at ambient levels.
The analytical challenges present in addressing today's environmental problems are formidable. In many instances the species of interest is present at very low levels, from nanomolal to picomolal concentrations, and contamination is extremely difficult to avoid. Environmental samples generally involve analytically complex media. For example, sea water has a constant composition of major ions, but contains every element known to man; atmospheric aqueous phases which cover the gamut from dilute rain water to aerosols with ionic strengths near 15 molal and pH's less than 1. Often the species of interest and which are important in forcing chemical cycles are transient with life times from hours to seconds. Coupled to these difficulties in characterizing the spatial and temporal distribution of compounds in the environment are the analytical precision and accuracy which are needed to make meaning full insights from the time varying distributions of chemical species.
My research program continues to work towards developing in situ analytical instrumentation and sampling systems for chemical species in natural environments. The recent interests in coastal processes and the development of global chemical models both require enhanced spatial and temporal resolution in data collection. The most cost effective means of enhancing our data collection capabilities is through the development of instrumentation and robust analytical methods that are amenable to deployment on moored buoys for long term monitoring. Continuous, long term data sets for nutrients, oxygen, sulfide, and trace elements would enable improved modeling of complex coastal processes and yield the data necessary to evaluate long term temporal trends in the concentrations of environmentally important chemical species.
Creative application of analytical techniques to evaluate the effect chemical speciation has on the distribution, reactivity, and bioavailability of trace metals in natural waters and the influence trace element redox chemistry has on primary production.
Speciation of Iron in Seawater---The chemical speciation of iron profoundly influences its bioavailability (Anderson and Morel 1982) in oceanic waters and depends upon the relative importance of a variety of competing processes, including complexation with organic and inorganic ligands, adsorption-desorption, precipitation-dissolution, ion exchange and oxidation-reduction (redox) reactions. Although these chemical processes are complex, through careful method development and innovative sampling strategies the complexity can be resolved. The recent hypothesis that iron may be limiting to primary production in high nutrient, low chlorophyll regions of the worlds oceans has brought the difficulties of sampling and analysis of this element to the forefront of research and stimulated renewed interest in its environmental chemistry (Martin et al 1989, 1990). Iron is an essential micro nutrient, and processes altering its speciation and bioavailability are not fully understood. In addition the chemistry of iron may impact the distribution of other trace metals through adsorption and coprecipitation reactions. Studying trace metals in the open ocean is difficult since samples can be easily contaminated during collection and analysis. Trace levels of iron combined with its ubiquitous occurrence in the environment requires the most rigorous approach to clean sampling and post sampling manipulations. However, just determining the concentration of iron in the environment, although analytically challenging, is inadequate, we must understand its redox chemistry and speciation to evaluate what fraction of iron is biologically available. The toxicity of many trace elements has also been linked to their chemical speciation. My research in this area is focusing on the role superoxide plays in the redox chemistry of iron in natural waters.
Characterization and analysis of hydrogen peroxide and organic peroxides to enhance our understanding of radical transient production through photochemical reactions in the gas and aqueous phases in natural systems.
The primary objective of this work is the measurement of hydrogen peroxide (HP) and methylhydroperoxide (MHP) in the lower troposphere and in experimental chambers. These gases are directly coupled to the chemistry of ozone, hydroxyl radical, and nitrogen trioxide, which convert reduced sulfur gases to sulfuric acid and other products. HP and MHP are effective aqueous oxidants of dissolved SO2 under acidic conditions, and together with O3 and molecular oxygen are the principal oxidants of SO2 in water droplets. Improving our understanding of peroxides gas phase chemistries and gas-to-aqueous transfer will enhance our understanding of photochemical smog formation, and destruction and the atmospheric chemistry of sulfur containing compounds.