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

We measured the concentrations of Cl-, NO3- and SO42 - in atmospheric cloud water collected with a passive collector from a remote marine site and the concentrations of Cl-, NO3-, SO42 -, Na+ and NH4+ in cloudwater from a cont inental site. At the continental site, an active rotating arm collector was employed for cloudwater collection. At both locations, we observed an inve rse relationship between the measured ion concentrations and the liquid wat er content of the clouds. The product of the observed concentrations and th e liquid water content, the cloudwater loading, was found to be nearly cons tant. A study of published cloudwater data showed that at the majority of t he 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 hydr o-meteors Juring fog and cloud formation. (C) 2000 Elsevier Science Ltd. Al l rights reserved.