The Size and Number Distribution of Aerosols in the Continental Troposphere

A series of 22 aerosol collections made during the year 1966 at altitudes to 10 km in the vicinity of Scottsbluff, Nebr., have been analyzed. Several additional samples were taken at other locations in the centralUnited States when low tropopause conditions permitted collecting in the lower stratosphere. A few additional measurements were made over Limon, Colo. The sampling device was a single stage impactor mountedin a Beech Queen Air aircraft. Particle size and number distributions were determined by direct countingfrom photomicrographs. The collecting and counting techniques are described and the experimental resultspresented. Systematic changes were observed in the aerosol distribution function with altitude in whichboth the large and small particulates diminish with height. Short term variations in the size and numberdistribution, seasonal changes, and correlations with various meteorological parameters were investigated.Characteristic aerosol distribution functions for tropospheric and lower stratospheric air were found onoccasions of low tropopause. Correlations of the total number of large and intermediate size particles withrelative humidity and a more or less constant mixing ratio of intermediate sized particles with altitudesuggest the importance of cloud modification processes in determining the aerosol distribution function.