Nucleation, heteromolecular

Roedel, W., Measurement of Sulfuric Acid Saturation Vapor Pressure Implications for Aerosol Formation by Heteromolecular Nucleation, J. Aerosol Sci., 10, 375-386 (1979). 

Nucleation processes, especially in nature, are rarely homomolecular and homogeneous usually two species are involved (binary heteromolecular nucleation), and foreign surfaces may also be present (heterogeneous... 

Kiang, C. S Stauffer, D Mohnen, V. A., Bricard, J. and Vigla, D., 1973 Heteromolecular nucleation theory applied to gas-to-partide conversion. Atmospheric Environment 7, 1279-1283. 

Jaecker-Voirol, A., and Mirabel, P. (1989) Heteromolecular nucleation in the sulfuric acid-water system, Atmos. Environ. 23, 2053-2057. 

Heterogeneous-heteromolecular nucleation of two or more species on a foreign substance. 

FIGURE 11.12 Composition of the critical H2S04-H20 nucleus, calculated for / = 1 cm-3 s, as a function of RH. The different curves correspond to the temperatures shown. (Reprinted from Atmos. Environ. 23, Jaecker-Voirol, A. and Mirabel, P., Heteromolecular nucleation in the sulfuric acid-water system, p. 2053, 1989, with kind permission from Elsevier Science Ltd, The Boulevard, Langford Lane, Kidlington OX5 1 GB, UK.)... 

Stauffer, D. (1976) Kinetic theory of two-component ( heteromolecular ) nucleation and condensation, J. Aerosol Sci. 7, 319-333. 

We have seen that in homogeneous-homomolecular nucleation, nucleation does not occur unless the vapor phase is supersaturated with respect to the species. When two or more vapor species are present, neither of which is supersaturated, nucleation can still take place as long as the participating vapor species are supersaturated with respect to a liquid solution droplet. Thus heteromolecular nucleation can occur when a mixture of vapors is subsaturated with respect to the pure substances as long as there is supersaturation with respect to a solution of these substances. The theory of homogeneous-heteromolecular nucleation parallels that of homogeneous-homomolecular nucleation extended to include two or more... 

We see that at the lower SO2 conversion rate, the characteristic time for nucleation to occur greatly exceeds that for condensation so the latter can be expected to predominate as the mechanism for gas-to-particle conversion. At the higher production rate at high humidities, the nucleation time can actually become shorter than the condensation time, indicating that heteromolecular nucleation can be expected to become important under these conditions. 

It appears feasible to analyze the homogeneous nucleation process by molecular dynamics for molecules with spherically symmetric potentials, but the next step-extension to nonsymmetric potentials —appears to be almost prohibitive at present. The much more important nucleation processes-heteromolecular nucleation and heterogeneous nucleation, for example-must still be approached by phenomenological theories. 

---