Using an upward thermal diffusion cloud chamber specially designed for
operation at elevated pressures and temperatures, we have observed a
strong dependence of the homogeneous nucleation of 1-propanol vapor on
total pressure. In our investigation, this dependence is manifested i
n increasing values of the measured S-crit (critical supersaturation)
of 1-propanol with increasing total pressure. The increase in total pr
essure is accomplished by increasing the amount of a carrier (or backg
round) gas in the diffusion cloud chamber. The observed increase in me
asured S-crit implies that the homogeneous nucleation rate of 1-propan
ol decreases dramatically as the total pressure increases. We have obs
erved a significant dependence on the nature of the carrier gas. The e
ffect of increasing total pressure on the nucleation of 1-propanol is
greater using helium as the carrier gas than when hydrogen is used. We
also observe that the dependence of S-crit on total pressure (as mani
fested by the slope of the S-crit vs P-tot data at constant temperatur
e) is temperature dependent. The measured slope of the S-crit vs P-tot
dependence increases as the temperature decreases. In addition, we pr
esent S-crit vs temperature data for the 1-propanol/helium system that
appear to span the widest range of temperatures to date.