The Proportion of Volatile Aerosols on the Island of Hawaii

Abstract

Nephelometry, in conjunction with a tube furnace and an Aitken nuclei counter, has been applied to the investigation of the volatile component of the aerosol budget at Cape Kumukahi, Hilo. and Mauna Loa Observatory, Hawaii. It was found that heating of the incoming air sample resulted in a decrease in light scattering above 100C due to the loss of organics and other easily volatilized compounds, and a drastic increase in Aitken nuclei counts at temperatures above 150C in the presence of ammonium sulfate. In the marine aerosol, a decrease in light mattering at about 45C was observed which is probably due to the loss of moisture during the phase transition from droplet to crystal. A second decrease near 120C is probably caused by the volatilization of organics from the droplet aerosol. In heating to 150C, the amount of light-scattering decrease was found to depend on the air mass. On occasions when volcanic effluent was apparently present, an increase in Aitken nuclei was noted in the heated air. Total aerosol mass deduced from light-scattering measurements before heating was in good agreement with aerosol mass measurements determined by standard high-volume filter sampling techniques. The total amount of aerosols in the air mass above the trade inversion is comparable to the quantity found in the marine air man. After penetrating the trade inversion, however, the cation content of the air is significantly reduced and the aerosol volatility is increased.