Spring 2003 Departmental Distinguished Seminar Series

Professor Jeffrey L. Collett, Jr.

Colorado State University
"Pollution Processing by Clouds and Fogs"
January 31, 2003

Jeffrey Collett provided an overview of the chemical compositions of fogs and clouds measured in a series of field experiments across the United States and highlighted the roles these clouds and fogs play as processors of atmospheric pollution. Together with gases and particles, clouds and fogs comprise a complex multiphase system. Collett explained how clouds act as processors of atmospheric aerosol particles and trace gases and as aqueous reactors for the production of new chemical species. He went on to explain some of the key processes involved. He also addressed recent evidence that suggests clouds are not only active processors of inorganic atmospheric compounds but of organic compounds as well. Collett’s visit was hosted by Kalliat Valsaraj.

Professor George W. Roberts

North Carolina State University
"Continuous Chain-Growth Polymerization in Supercritical Carbon Dioxide"
February 7, 2003

George Roberts explained how most commercial polymerizations are carried out in organic solvents or in water, resulting in large quantities of gaseous and/or liquid waste. However, he noted that using supercritical carbon dioxide (scCO2) as a reaction medium is an exciting new way to avoid such waste streams and that, in many cases, carrying out a polymerization in scCO2 also results in significant energy savings. The surfactant-free, precipitation polymerizations of acrylic acid and vinylidene fluoride have been carried out in scCO2 using a continuous stirred-tank reactor (CSTR). The kinetics of vinylidene fluoride polymerization were studied in some detail, using diethylperoxydicarbonate (DEPDC) as the free-radical initiator. The effects of inlet monomer concentration, temperature, average residence time, and agitation on the polymerization rate, the average molecular weights, and the molecular weight distribution were investigated. Roberts went on to discuss the specifics of this polymerization. Roberts’ visit was hosted by Jerry J. Spivey.

Professor Anthony J. C. Ladd

University of Florida
"Dynamics and Structure in a Settling Suspension"
February 21, 2003

During the seminar, Anthony Ladd summarized results from computer simulations of particles settling in a low-Reynolds number regime. He explained how the fluid flow is calculated using a lattice-Boltzmann model, which is coupled to the particle dynamics via a no-slip boundary condition on the surfaces of the individual particles. Finally, he compared results for the dynamics and microstructure of settling suspensions with available experimental measurements and examined current theoretical ideas in the light of these simulations. Ladd’s visit was hosted by Karsten Thompson.

Professor Joel Baker

University of Maryland/Chesapeake Biological Laboratory
"Geochemistry on a Dinner Plate: Organic Contaminant Dynamics in the Chesapeake Bay"
March 28, 2003

The Chesapeake Bay is the largest estuary in North America. The 64,000 square mile watershed surrounds a bay that is about 200 miles long and ranges in width from 3.4 miles to 35 miles. More than 15 million people live in the Chesapeake Bay watershed. The bay holds more than 7 x 1010 m3 of water, much of which is spread in a thin veneer over the sediments with much of the bay’s waters less than 3 meters deep. The geochemistry of the Chesapeake is, therefore, dominated by loadings from the watershed and exchange of chemicals across the sediment-water and air-water interfaces. Joel Baker explained that for the past 12 years, he and others have conducted field studies of chemical contaminant cycling in the Chesapeake Bay with the broad goal of understanding how the estuary processes materials it receives from the landscape. He focused his discussion on the behavior of polychlorinated biphenyls (PCBs), a well-studied class of persistent hydrophobic organic chemicals. Baker’s visit was hosted by Louis Thibodeaux.

Professor David Allen

University of Texas-Austin
"The Texas Air Quality Study: State of the Science of Air Quality in Texas and Implications for Air Quality Policy"
April 4, 2003

David Allen is one of four lead investigators for TexAQS. He provided an overview of the study and discussed both the policy implications of the study as well as the enhanced understanding of urban atmospheric chlorine chemistry that emerged from the study. In short, the TexAQS was the largest air quality field study ever undertaken in Texas and one of the largest ever done anywhere in the U.S. During August and September of 2000, approximately 300 air quality investigators from around the world converged on Houston, Texas. The scope, goals, and preliminary results are available at the study website, www.utexas.edu/research/ceer/texaqs. Allen’s visit was hosted by Danny Reible.

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