Dr. Paul Ziemann

Atmospheric Aerosol Research - University of Colorado, Boulder

Our research involves experimental studies of the chemistry of submicron atmospheric aerosol particles. Particles in this small size range are generally formed by combustion or by a process referred to as gas-to-particle conversion, which is often quite complex and can include photochemical gas-phase reactions, heterogeneous surface chemistry, homogeneous nucleation, and liquid-phase reactions. The resulting particles play important roles in a number of atmospheric phenomena. For example, aerosol particles serve as condensation nuclei for the formation of clouds, which exert a major influence on global climate and in polar regions are critical to the formation of a stratospheric ozone hole. In urban environments, photochemical reactions involving volatile organic compounds, oxides of nitrogen and sulfur, and atmospheric oxidants produce condensable species, which in turn form particles that can affect visibility and human health. Furthermore, heterogeneous reactions on particle surfaces can affect the lifetimes and physico-chemical properties of atmospheric particles. The chemistry of aerosol particles and the processes that determine their composition and distribution in the atmosphere are still poorly understood.

In our research we use a thermal desorption particle beam mass spectrometer we have developed, in conjunction with other tools for aerosol sampling and size and composition analysis, such as cascade impactors, differential mobility analysis, Fourier transform infrared spectroscopy, and gas chromatography-mass spectrometry, to investigate fundamental processes responsible for gas-to-particle conversion in the atmosphere. In particular, our work is aimed at elucidating the mechanisms by which the atmospheric oxidants O3, OH, and NO3 oxidize volatile anthropogenic and biogenic organic compounds to form condensable compounds which form particulate material. Information on the products and mechanisms of reactions of gaseous and condensed-phase species, as well as compound thermochemical properties such as vapor pressure are obtained from environmental chamber studies. These tools are also used in studies of heterogeneous oxidation of organic aerosol particles and particle formation in combustion systems, such as diesel engines. The results of these studies further our understanding of atmospheric aerosol chemistry and the impact of human activities on the atmospheric environment.