UPPER-TROPOSPHERIC AEROSOL SAMPLED DURING PROJECT FIRE-IFO-II

During the FIRE IFO II project, aircraft were available for airborne s ampling in and around cirrus clouds. Aerosols can play a role in the c loud formation process through the heterogeneous nucleation mechanism, and in turn, once formed, cirrus clouds can impact the ambient aeroso l through scavenging and other collection mechanisms. University of Mi ssouri aerosol sampling facilities were employed on these aircraft for in situ collection and characterization of the particulates near cirr us cloud level. Tandem differential mobility analyzer and impactor tec hniques were used to measure aerosol size distribution, hydration capa bility, and particle composition information. Evidence of aerosol laye ring was observed near the tropopause, and there was a tendency toward depletion of the ambient aerosol at both ends of the condensation nuc lei (CN) size distribution. A large variability in the fine particle C N concentration was found, ranging from several tens to several thousa nds per cubic centimeter. The size distribution of particles larger th an 0.5 mu m roughly followed a lognormal relationship and large partic le concentrations varied between 0.127 and 1.70 cm(-3). The particulat es were found to be of mixed character, primarily inert with a small p ercentage of soluble material. A large variability in particulate conc entrations was found.