Paul O. Wennberg

R. Stanton Avery Professor of Atmospheric Chemistry and Environmental Science and Engineering; Executive Officer for Environmental Science and Engineering; Director, Ronald and Maxine Linde Center for Global Environmental Science
B.A., Oberlin College, 1985; Ph.D., Harvard University, 1994. Associate Professor of Atmospheric Chemistry and Environmental Engineering Science, Caltech, 1998-2001; Professor, 2001-03; Professor of Atmospheric Chemistry and Environmental Science and Engineering, 2003-04; Avery Professor, 2004-; Director, Linde Center, 2008-11; Executive Officer, 2012-; Acting Director, Linde Center, 2012-14; Director, Linde Center, 2014-.
My research group applies traditional physical chemistry techniques (e.g. LIF, absorption spectroscopy, mass spectroscopy) to study the mechanisms of chemical transformation in the Earth's atmosphere. Through these studies, we wish to understand the oxidative chemistry of the atmosphere and how this chemistry is influenced by and in turn influences the biosphere. An important component of this research effort is to understand the influence of anthropogenic activity on the global atmosphere.

In the laboratory, we are studying the interactions of ultraviolet, visible, and infrared radiation with a number of important atmospheric trace gases. The aim of this work is to better elucidate the coupling of radiation and chemistry in the upper troposphere and lower stratosphere. The photodissociation of a number of gases (e.g. nitric and peroxynitric acids, and HOONO) in this region of the atmosphere occurs in the spectral region between 310 and 400 nm. In general, the rate of photodissociation is poorly known because the cross sections and photo-physics are not well characterized at these wavelengths. In our laboratory, we have coupled a tunable OPO laser system with a highly sensitive laser induced fluorescence detection system to accurately measure the product of the quantum yield and the absorption cross section for a number of species. We are using model calculations of the transmission of sunlight through the atmosphere to interpret these measurements within the context of the atmospheric photochemistry.

We have also developed a new class of instrumentation for airborne measurement of a number of acids and bases that contribute to the formation of atmospheric aerosol. In a collaborative effort with Caltech Prof. Richard Flagan and Dr. Fred Eisele's (National Center for Atmospheric Research), we have built a selected ion chemical ionization mass spectrometer for use on the NASA ER-2 and the DC8. The aim of these studies is to characterize the composition of both the gas and aerosol phases. We measure in situ the concentrations of a number of acids and bases (such as nitric acid, sulfuric acid, and ammonia). In this way, we are working to understand both the mechanism for the production of aerosol and the influence of heterogeneous chemistry occurring in and on these particles. This instrument first participated in the NASA SOLVE campaign, January - March, 2000, Kiruna, Sweden.

More recently, my students Rebecca Washenfelder and Zhonghua Yang, together with JPL scientists Geoff Toon and Jean-Francois Blavier, have begun development of a high resolution spectrograph for measurement of the column burden of CO2. These observations provide a new constraint on the global carbon cycle and, in addition, are aimed to help validate future space-based observations of the same quantity.


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