摘要：The composition of cloud droplet nuclei was compared to the composition of ambient
aerosol particles in non-precipitating clouds in different regions. Single-particle electron
microscope techniques were used to identify particle types. The smallest particles
(<0.2 µm diameter) exhibited a dependence of composition on nucleating ability, with salts (chlorides
and sulfates of Na, K, Ca and Mg) being preferred nuclei types, followed by ammonium
sulfates and organics. Crustal and industrial metals were less likely to be incorporated into
cloud droplets. However, for experiments where only larger particles were sampled, a
weaker dependence on composition was found. This suggests that larger particles
have sufficient soluble material to nucleate despite their primary type. Both size
and composition seem to be important, with composition becoming increasingly
important as smaller particles activate at higher supersaturations in the cloudy
environment.
