Vertical profiles of cloud condensation nuclei at midcontinential sites through the development and use of a balloon-borne instrument

A balloon-borne instrument was developed for observations of vertical profiles of cloud condensation nuclei (CCN) number concentration. The CCN concentration is deduced from measurements of the laser light scattered by water droplets that activated on CCN within a cloud chamber. The amount of light scattering is proportional to the number of droplets that form within the chamber. The instrument is calibrated by correlating the number of droplets within a sample volume with the amount of scattered light. The balloon-borne CCN counter has been flown on 12 balloon flights at Laramie, Wyoming (41°N) and 2 balloon flights at Lauder, New Zealand (45°S). The instrument gondola for each of these flights also contained a condensation nuclei (CN) counter and an optical particle counter to measure aerosols with diameter greater than 0.3 mum (D0.3). The vertical profile measurements from the 14 flights have been summarized by classifying them into five distinct atmospheric layers: surface, lower tropospheric, upper tropospheric, stratospheric and regions of high humidity. Laramie summer and winter profiles show that the mean CCN concentration decreases between the lower and upper tropospheric layers (445 cm-3 to 126 cm-3 in summer; 146 cm-3 to 64 cm-3 in winter). Variations in the vertical profile of CCN concentration were typically positively correlated with changes in CN and D0.3 concentrations, and often corresponded with changes in relative humidity, typically being positively correlated but sometimes negatively correlated. The CCN/CN ratio typically increases between the lower and upper troposphere. The summer CCN concentrations at Lauder, New Zealand (45°S) were about twice the summer CCN concentrations measured at Laramie, Wyoming (41°N) while the CN and (D0.3). concentrations were about the same.