Control of solute concentrations in cloud and fog water by liquid water content

We measured the concentrations of Cl−, NO3−, and SO42− in atmospheric cloudwater collected with a passive collector from a remote marine site and the concentrations of Cl−, NO3−, SO42−, Na+ and NH4+ in cloudwater from a continental site. At the continental site, an active rotating arm collector was employed for cloudwater collection. At both locations, we observed an inverse relationship between the measured ion concentrations and the liquid water content of the clouds. The product of the observed concentrations and the liquid water content, the cloudwater loading, was found to be nearly constant. A study of published cloudwater data showed that at the majority of the examined locations this product varied little at any given site, whereas large differences exist between sites. The finding of the small variation in cloudwater loadings could be explained by the hypothesis that nucleation scavenging is the dominant process in the acquisition of solutes into hydro-meteors during fog and cloud formation