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. T... 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. T...