Cloud Condensation Nuclei from a Paper Mill. Part II: Calculated Effects on Rainfall

Abstract

The paper mill at Port Townsend, Wash., is a source of large and giant condensation nuclei (CCN). These CCN cause the concentrations of droplets ≥30 ?m in diameter to be higher in small, nonraining warm clouds located in the plume of the mill than in similar clouds unaffected by the plume. Calculations based on a model for nonsheared, warm cumulus clouds and a model for warm stratus clouds indicate that the higher concentrations of large droplets in the clouds in the plume should not cause any significant changes in the rainfall from these clouds. These results indicate that the large and giant CCN emitted by the mill are not by themselves responsible for the increased rainfall measured in the vicinity of the mill. The heat and moisture emitted by the mill, in combination with the CCN, may have been responsible for the increased rainfall.