The Vertical Distribution of Cloud and Aitken Nuclei Downwind of Urban Pollution Sources

Abstract

Simultaneous airborne observations of Aitken and cloud nuclei upwind and downwind of Buffalo, N.Y., were made in an effort to determine the effects of air pollution on condensation nucleus concentration. The data show significant increases over background concentrations of both Aitken and cloud nuclei (at 0.3% supersaturation) immediately downwind of pollution sources, and, also, that a secondary maximum in cloud nucleus concentration usually occurs about 10–15 mi farther downwind. In spite of these large increases in the total number of nuclei downwind of an industrial-urban complex such as the Niagara Frontier, the concentration of cloud and Aitken particulates approaches upwind background levels within 20–50 mi of the sources. Attempts to define the role (if any) of air pollution in cloud microstructure were confined to a single set of airborne observations. The limited drop-size distribution and cloud nucleus data were not sufficient to justify firm conclusions, and additional measurements are recommended.