The Segregation of Aerosols by Cloud-Nucleating Activity. Part II: Observation of an Urban Aerosol

Abstract

The submicron aerosol of metropolitan Seattle was segregated into CCN and non-CCN fractions by a high-flux thermal diffusion cloud chamber in series with a dichotomous separator. Each segregated fraction of the five-hour daily sample was deposited on a filter, and analyzed for mass, optical absorption, sulfate and nitrate. Results are presented in context with the meteorological record. A new finding of this study is that the mean non-CCN mass fraction of the submicron aerosol was greater than 50%. The sulfate, nitrate, and optical absorption partitioned between the CCN and non-CCN fractions. The mean ratio of optical absorption to mass concentration suggests that both the non-CCN and CCN fractions contain soot. The CCN optical absorption and sulfate concentration am modulated by rainfall events.