Chemistry @ Colgate

Ephraim Woods III

Research Projects Description

The Structure and Heterogeneous Chemistry of Liquid Surfaces Studied by Aerosol Particle Photoionization

Heterogeneous processes that take place on aerosols in the troposphere affect many aspects of climate including radiation balance, cloud condensation kinetics, and air pollution.  Despite the recognized importance of the gas-liquid interface in the atmosphere, there are many unresolved (and unaddressed) problems in heterogeneous chemistry stemming from the lack of molecular-level probes of the liquid surface.  Among these fundamental topics are the unique bonding and orientation of surface molecules, the location (surface or bulk) of reaction sites, and the existence of catalytic and photochemical processes specific to the interface.  Our experiments address these problems with molecular-level detail using a new laser spectroscopic probe of aerosol particles (~100 nm in diameter). 

            This new technique, which is based on the laser multiphoton ionization of aerosol particles (shown in the figure), is sensitive only to species near the surface of the particles and can both monitor the concentration of trace species adsorbed to the surface and measure their ultraviolet absorption spectrum.  By monitoring the concentration of a reactant molecule on the surface of an aerosol particle as a function of the particle’s exposure to another reactive gas (like ozone), we can measure the rates of important reactions in tropospheric chemistry.  These kinetic measurements will aid in creating more accurate atmospheric models.  Furthermore, since a molecule’s ultraviolet absorption spectrum depends strongly on its local environment, species on the surface of liquids often have drastically different spectra than those in the bulk phase.  Therefore, our spectroscopic measurements will provide information about the structure of the surface.  (For example -- which part of the molecules likes to stick up into the air and which part likes to bury itself in the liquid?)  These structural details are useful in understanding gas uptake rates and chemical reactivity of aerosols.

Further Readings

To learn about some important issues regarding aerosols in the troposphere, read:

For information about photoelectric charging of aerosols (a technique closely related to the one we will develop here), read:


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