Cloud Condensation Nuclei from a Paper Mill. Part I: Measured Effects on Clouds

Abstract

The effluents from a large Kraft-process paper mill were found to increase the concentration of large (0.2?2 ?m diameter) and giant (>2 ?m diameter) cloud condensation nuclei (CCN) above background concentrations; the concentrations of small (<0.2 ?m diameter) CCN, however, were not increased significantly. Small, nonraining, warm cumulus clouds located in the plume of the paper mill were found to contain higher concentrations of droplets ≥30 ?m diameter than similar clouds located outside of the plume; the clouds in both locations contained similar concentrations of droplets ≥5 ?m diameter. Cloud droplet size distributions calculated using the CCN measurements are consistent with the measured droplet size distributions. It is concluded that the large and giant CCN from the paper mill increased the concentrations of droplets ≥30 ?m diameter in clouds located in its plume. Furthermore, the clouds located in and out of the plume contained similar concentrations of droplets ≥5 ?m diameter because the concentrations of small CCN in the plume and in ambient air were similar.