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Aerosols can have important influences on climate and the radiation balance of the
atmosphere. However, the temporal and spatial variability of aerosols and our inadequate
knowledge of aerosol optical properties have lead to large uncertainties in these effects.
Thus improved in-situ measurements of aerosol optical properties, in particular
measurement of their extinction coefficients, are required. Recently, the relatively new
technique of cavity ring-down (CRD) spectroscopy has been applied to the problem of
making fast, accurate measurements of aerosol extinction coefficient. The CRD
instruments can routinely measure sub-Rayleigh equivalent extinction levels of a few
Mm-1Hz0.5 and are generally more rugged and portable than traditional extinction cells.
Possible applications of CRD-based extinction cells include studies of visibility, climate
forcing by aerosol, and the validation of aerosol retrieval schemes from satellites such as
MODIS, MISR, and CALYPSO.
This paper will present the motivation for making improved aerosol extinction
measurements and discuss the problems in making the measurement. The cavity ring-
down technique will be described. In June, 2002, our instrument participated in an
extensive laboratory intercomparison, the Reno Aerosol Optics Study. We are currently
involved in a flight campaign in Monterey, Ca, called Asian Dust Above Monterey.
Examples of data collected during these experiments will be presented.
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