Structure and Heterogeneous Chemistry of Liquid Surfaces Studied by Aerosol
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.
learn about some important issues regarding aerosols in the troposphere, read:
information about photoelectric charging of aerosols (a technique closely
related to the one we will develop here), read:
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