Upper-Tropospheric Aerosol Sampled during Project FIRE IFO II

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Abstract
During the FIRE IFO II project, aircraft were available for airborne sampling in and around cirrus cloud. Aerosols can play a role in the cloud formation process through the heterogeneous nucleation mechanism, and in turn, once formed, cirrus clouds can impact the ambient aerosol through scavenging and other collection mechanisms. University of Missouri aerosol sampling facilities were employed on these aircraft for in situ collection and characterization of the particulates near cirrus cloud level. Tandem differential mobility analyzer and impactor techniques were used to measure aerosol size distribution, hydration capability, and particle composition information. Evidence of aerosol layering was observed near the tropopause, and there was a tendency toward depletion of the ambient aerosol at both ends of the condensation nuclei (CN) size distribution. A large variability in the fine particle CN concentration was found, ranging from several tens to several thousands per cubic centimeter. The size distribution of particles larger than 0.5 micro;m roughly followed a lognormal relationship and large particle concentrations varied between 0.127 and 1.70 cm−3. The particulates were found to be of mixed character, primarily inert with a small percentage of soluble material. A large variability in particulate concentrations was found.

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