THE NATURE OF AITKEN CONDENSATION NUCLEI IN THE ATMOSPHERE

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Abstract
Laboratory and field experiments have shown that organic substances, and specifically [alpha]-pinene, can form condensation nuclei (cn) when subjected to high light intensities in the presence of NO2 or I2 as light-absorbing catalysts. These nuclei range in size from 10-7 to 10-5 cm, in the same size range as the smaller Aitken nuclei in the atmosphere. In nature a daily rhythm in the concentration of cn is found it is lowest in the late night hours, rises suddenly about 20% during the 1st light hours (especially the nuclei of <0.13 [mu] diameter), increases another 10% during the rest of the day, and decreases again after sunset. In cities these cn are related to automobile traffic, in nature they parallel the production of organic vapors by the vegetation. Near the ground the number of cn decreases through: impaction with solid surfaces and agglomeration of the smaller particles. In the higher atmosphere 2 other mechanisms seem to control the cn: accumulation of cn in cloud surfaces, and precipitation of cn by rain and snow. Filtration of cn from the air indicates that at any one time about 1 x 10-4 mg particulate material is in the air over each cm2 of Ozark country; measurement of insoluble solids in rainwater indicates a total precipitation of 5 x 10-4 mg/cm2 of land surface per year. This suggests a world production of at least 500 x 106 tons of submicroscopic particulate organic matter per year.

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