Water Solubility of Cloud-Active Aerosols

Nineteen common electrolytes, which usually constitute the hygroscopic fraction of cloud-active aerosols (CAA), are examined for their solubility in water. Water droplets nucleated upon CAA have so far in the literature been treated as weak solution droplets. Upon examination of this assumption, it is revealed that sulfates that are so commonly found in urban-industrial and nonurban environments are least water soluble, and large errors are likely to be encountered if their nucleation-growth behavior is simulated based on the assumption of weak solution droplets. A new classification scheme is presented and all nineteen electrolytes are arranged in three groups according to their water solubility. Approximation formulas relating the critical supersaturation to dry state particle radius, critical radius, and radius at 100% relative humidity are examined and magnitudes of errors calculated, if the former are used regardless of the solute concentration in droplets. A method for correcting errors is presented for isothermal haze chambers.