Faculty Research Activities
Field Study Locations and Facilities
Three specialized walk-up atmospheric sampling towers have been installed at a Gulf Coast site near Galveston and at locations in a pine forest and an oak forest in Sam Houston National Forest in east Texas. The towers have been used often by investigators in other regions for field studies.
Aerosol Particle Measurements
Aerosol-sizing instruments presently employed in the Houston Supersite project have been installed at each tower. Aerosol particles are collected routinely for chemical analysis. Additionally, an instrument capable of measuring the composition of individual particles as small as 1 millionth of a cm can be operated at one or more of the towers. Together, these instruments provide much of the data essential to understanding the physical and chemical properties of the aerosol. By locating one tower near the Gulf coast and the others in different types of forests inland, details of the marine, urban, and forest-influenced aerosol particles and their transformations can be obtained. These measurements can be used to identify sources of the particles and, in conjunction
with other instruments, determine the effect of chemical speciation on such aerosol physical properties as hygroscopicity, scattering efficiency, and cloud condensation nuclei (CCN)-forming potential. Knowledge of the composition of CCN both at the inland and coastal sites is critical in improving our understanding of the climatic implications of changing CCN concentrations.
Quantitation of ozone, NOx, SO2, CO and volatile organic compounds (VOCs) such as hydrocarbons in the atmosphere are being made. Vegetative sources exceed anthropogenic sources for hydrocarbons globally. Understanding biogenic hydrocarbons is important because isoprene and terpenes, emitted by oak and pine forests respectively, contribute more than 80% of the global VOCs produced by vegetation. Isoprene plays an important role in producing ozone while terpenes are major precursors for aerosol formation. Stable carbon isotope measurements of VOCs will also be made to determine the various sources of these organic compounds.
Laboratory investigations focus on the molecular level kinetics and mechanisms of gas-phase and heterogeneous reactions concerned with the modeling of chemistry and transport of urban and regional air pollution. The catalytic mechanisms by which free chlorine and bromine deplete stratospheric ozone are well recognized. However, significant uncertainties remain regarding the chemistry and degradation pathways of halogen mediated chemistry in the troposphere. The chemistry and physical properties of transient species containing chlorine and/or bromine, particularly those that are photochemically labile, represent fundamental gaps in experimental information relevant to characterization and modeling of these processes. Transient species that involve weakly bound species may also be extremely important in tropospheric chemistry of the marine boundary layer. The complex halogen chemistry that exists in shipping lanes requires a characterization of interactions between halogen atoms, derived from sea spray, with hydrocarbons of anthropogenic origin, a serious consideration over the Gulf of Mexico. Research will focus initially on the development of submillimeter spectrometric techniques to detect and state characterize molecular species relevant to atmospheric chemistry. Ultimately such research will be used to quantify the abundance of these species in the atmosphere. Once the experimental generation and spectroscopic characterization has been achieved the chemical reactivity can then
be studied to assess the local impact of this chemistry. Such studies will focus on the formation of intermediate radicals arising from the hydrocarbon reactions and their subsequent degradation reactions. In addition, high level calculations will be performed to study the structures and energetics of the relevant radical species using the Texas A&M Supercomputer Facilities.
Atmospheric modeling is initially focused on the local and regional processes governing the transport and diffusion of atmospheric constituents. Southeast Texas is subject to a variety of locally generated circulations (land-sea breeze, winds induced by land use changes, and the diurnally forced low-level jet). Understanding these phenomena through simulations with the National Center for Atmospheric Research (NCAR) MM5 model and comparisons with observations will be essential to determine the meteorological and emissions history of the air sampled at the towers.
Chemical Transport Modeling
In order to understand the chemical processes that take place on the local and regional scales, a leading mesoscale chemical transport model (CTM) is being coupled to the MM5. This CTM obtains its boundary conditions from an NCAR global model known as MOZART. Laboratory and field measurements will lead to improvements in the CTM's handling of chemical reactions. As the model improves, the CTM will become an increasingly valuable tool for the understanding of chemical processes that take place at local and regional scales.
Molecular and Nanoscale Aerosol Modeling
The presence of water on typical combustion generated aerosol particles is pivotal to several crucial issues in urban and regional air quality and global climate change. A framework is needed for understanding, anticipating, and accounting for water on particles, for interpreting relevant atmospheric data, and for improving atmospheric models. This work involves theoretical research and numerical simulations at the molecular and nano-scales describing water and its effects on aggregates of nanometer particles representative of those produced by combustion. These calculations also will be valuable for including the effect of water on aerosol particles in a model such as the CTM.
Contributions of reliable information to support public policy decisions
The products of the environmental molecular science teams associated with the proposed Environmental Molecular Science Institute (EMSI) are expected to advance the basic science of their underlying disciplines and their contributions to understanding the natural and anthropogenic processes that affect air quality. To insure that research products find their way into the mainstream of policy and application, it will be necessary to understand the process of how scientific information and discoveries related to air quality are received, understood, evaluated and used by decision-makers and the public. This will be achieved through the activities of the Institute for Science, Technology and Public Policy, Bush School of Government and Public Service.
Institute for Physics of Microstructures of Russian Academy Sciences, Nizhny Novgorod, Russian
An active collaboration involves the group of Dr. Vladimir Vaks, head of the Department of Microwave Technique and Spectroscopy of Institute for Physics of Microstructures of Russian Academy Sciences, Nizhny Novgorod, Russian. Dr. Vaks is a world reknowned scientific expert in the discipline of generation and application of submillimeter and Terahertz waves for scientific purposes. He, together with his research group, have been interacting with the Bevan research group at the Chemistry Department, Texas A&M University in the development and application of spectroscopic instrumentation for the last four years. This has now resulted in the development of a state-of-the-art phase and frequency stabilized submillimeter/terahertz spectrometer suitable for investigating the modeling of how molecules interact through weakly bound intermolecular forces and for applications to diagnostics and monitoring of atmospheric pollution. We hope our research can now be extended in future collaborations to prototypical devices that can detect molecules that pollute the atmosphere such as nitrogen oxides and carbon monoxide that are generated by normal automobile emissions and other urban emission sources. Most important are the possibilities of extending our cooperation and interactions especially for those associated with research projects connected to the Center.