We are keenly interested in applying a variety of physical methods to relevant problems in:

heterogeneous atmospheric chemistry	environmental photochemistry
single-particle aerosol analysis	electron-transfer chemistry

There are a number of intriguing aspects, ranging from fundamental questions of chemical dynamics to relevant issues of human health, that are being addressed in these studies. A key component of our research effort is the continuing development of new experimental methods, many of which involve mass spectrometric and laser-based approaches. Computational models also figure prominently in the analysis and evaluation of the experimental data. The diverse nature of the work has naturally led to collaborations with scientists from the fields of chemistry, physics and engineering and a close association with the OSTC and CGRER.

Heterogeneous Atmospheric Chemistry

Solid particulates, such as soot from combustion processes or mineral aerosol from windblown soil, are an important, yet little studied, component of the earth's atmosphere. We have constructed a large atmospheric reaction chamber to investigate the interaction of aerosol particles with gaseous reactants under conditions that closely mimic those found in the troposphere. A range of techniques, such as IR and UV/Vis absorption and laser induced fluorescence, are used to monitor the reaction and extract kinetic information. Our goal is to produce quantitative parameters that can be used as input for detailed computer models of the atmosphere in order to evaluate the role of aerosols on the global ozone balance and their influence on global warming phenomena.

Single-particle aerosol analysis

We are actively developing mass spectrometric methods for the analysis of single aerosol particles in real-time. A number of applications in heterogeneous atmospheric chemistry and environmental monitoring would benefit from such instrumentation. For example, we have modified a time-of-flight mass spectrometer (TOFMS) to sample airborne biological particulates, such as microorganisms and microbial products. The isolated particles are size-selected using a laser scattering method and then probed using a combination of laser wavelengths. The resultant mass spectrum is used to identify and classify the particle in real-time. Our approach will aid studies of inhalation toxicology in contaminated environments, which require knowledge of the size-correlated chemical speciation as well as details regarding the distribution of airborne microorganisms.

Electron-transfer chemistry

Donor-acceptor complexes in the atmosphere, momentarily bound together by intermolecular forces, can undergo an electron-transfer (ET) process upon absorption of light. New reaction pathways mediated by the ET process, which is characteristic of the complex but not the isolated molecules, can influence atmospheric chemistry, particularly the photochemical oxidant cycle. We are examining complexes of atmospherically relevant species, such as O₂ and O₃, with various hydrocarbons. For instance, ET in alkene-O₂ complexes produces O atoms, an oxidative radical in the atmosphere, 10³ times more efficiently than in isolated O₂.

Environmental photochemistry

We are also applying a novel mass sensitive technique to the study of aqueous photochemistry in cloud, surface and ocean waters. Cloud water can produce a variety of oxidants, such as hydroxyl radical and hydrogen peroxide, upon exposure to sunlight. Irradiation of surface and ocean waters that contain organic carbon results in a complex series of photoredox reactions. Our studies are intended to provide new insight into the details of the photochemical processes in these systems.