Abstract Aerosol particles containing liquid terpenes do not act as cloud condensation nuclei; they do not initiate formation of cloud droplets in clouds. They do, however, act as ice-forming nuclei initiating formation of ice particles. Presence of sulfate ions in cloud droplets appears to make them susceptible to freezing at higher temperatures when in contact with some of the terpenes. Heterogeneous nucleation of ice at a liquid-liquid interface was found to take place at higher temperatures in aqueous ammonium sulfate solutions than in pure water. The averaged temperatures of the phase transition were −3.6, −4.7, −4.4 and −4.8°C for pine needle oil, α-pinene oxide, eucalyptol and linalool, respectively; the corresponding temperature increases were 4.7, 7.8, 3.6 and 6.7°C. Separation of terpene molecules by dilution in carbon tetrachloride produced a marked decrease in ice nucleation temperatures. It was suggested that the arrangements of dipoles at the interface have decisive influences on the phase transition. Temperature of ice nucleation in the presence of solutions of hexadecanol in carbon tetrachloride generally decreases with a decrease of its concentration; the highest temperature of −5.0°C was found at 10 −3 M of hexadecanol and 10 −1 M of ammonium sulfate.