9724941 Lowenthal In this project, a novel measurement approach will be developed with the goal of relating CCN (cloud condensation nuclei) activity, particle size distribution, and chemical composition. The objective is to determine those physical and chemical properties of aerosol particles that determine their ability to act as CCN. CCN measurements will be carried out on particles which have been dried and size segregated by two methods: (1) with a MOUDI cascade impactor, and (2) electrostatic classification with a DMA (differential mobility analyzer). The CCN spectra of the non-size segregated aerosol will be measured as well. Detailed chemical composition as a function of particle size will be determined from MOUDI cascade impactor samples. The detailed ionic, organic, and mineral composition of particles coupled with their critical supersaturation spectra will constrain the chemical mixing state of the CCN. Field sampling will be conducted at a coastal site (Point Reyes, CA), where the aerosol is mainly marine, and at an inland location (near Reno, NV) which is exposed to both clean- and polluted-continental conditions, and where the aerosol composition is expected to be more complex, dominated by nitrates, sulfates, organic and elemental carbon, and mineral dust.
