Cloud condensation nuclei

Abstract

In this study the supersaturation spectra of Cloud Condensation Nuclei (CCN) and the size distribution spectra of aerosols were investigated. These studies were conducted because it is believed that atmospheric aerosols, especially CCN, can affect the climate of the Earth. First, the size distributions of aerosols and the number concentrations of CCN were measured at different times in different meteorological airmass systems. The results indicate that the CCN supersaturation spectrum can be calculated from the size distribution of aerosols in only a few cases, suggesting that the direct measurement of CCN is of importance. Second, based on the measurements, a new general equation is proposed to describe the CCN supersaturation spectrum for some types of aerosols. The corresponding equation for CCN size distribution is derived. It is also shown theoretically that, with certain assumptions, the aerosol size distribution in the accumulation mode can be described by a bell-shaped distribution, in agreement with our measurements. The new equations are compared with actual data. Finally, a new method is devised to facilitate the measurement of CCN. The new instrument, which we call the "CCN Remover", separates CCN from the rest of aerosols by activation and removal. Together with a particle sizer, a new CCN measurement system, the CCN Remover Spectrometer, can provide information on both the supersaturation spectrum and the size distribution of CCN. Preliminary laboratory tests show close agreement between measurement results and theoretical predictions. The Remover Spectrometer was successfully tested in the NASA SCAR-B (Smoke, Clouds, and Radiation-Brazil) biomass burning experiment.