On the size distribution of water soluble particles in the atmosphere

Abstract

The size distribution of the mass concentration of some water soluble materials was measured by an impactor of three stages and membrane filters. It was found that about the half of the mass of sulfate and ammonium particles is in the range of Aitken nuclei. The size distribution of sulfate particles depends on the relative humidity of the air: more nuclei are in the Aitken size range if the relative humidity is smaller. The size distribution of chloride particles is rather different from that of sulfate and ammonium particles: only a small fraction of the total mass is in the Aitken range. Considering the stoichiometric proportion of the ammonium sulfate, it is an ammonium excess, which is greater in the case of smaller particles. It is not impossible that this ammonium excess is caused by the presence of ammonium hydroxide. It follows from these results that in the Aitken size range there are many sulfate and ammonium particles which may be active cloud nuclei even over the continents.