Model simulations of rainout and washout from a warm stratiform cloud

Calculations utilizing a one-dimensional, time-dependent stratiform cloud model with parameterized microphysics to study the washout and rainout of soluble trace gases are presented. It is shown that the in-cloud concentrations of relatively insoluble species remain essentially unaffected by the presence of cloudwater and rainwater, while the concentrations of highly soluble species are rapidly depleted within the cloud. Due to this depletion it is shown that for highly soluble species the below-cloud scavenging via washout can dominate over in-cloud scavenging via rainout; in-cloud, aqueous-phase cloudwater and rainwater concentrations can differ considerably and, near the cloudbase, cloudwater concentrations can exceed rainwater concentrations by factors of two to ten.