Growth mechanisms and size spectra of photochemical aerosols
A series of photochemical aerosol aging experiments were performed in which the complete time-dependent size spectra (diameter range 0.004 < dp < 0.35 micrometers) were measured using a Whitby aerosol analyzer. Based on these data, the role of various physical mechanisms, i.e., nucleation, coagulation, and condensation in the photochemical aerosol formation is identified. In an initially particle-free system, the aerosol passes through the following stages of evolution: nucleation-condensation (simultaneously), nucleation-condensation-coagulation, and condensation and coagulation. If suitable foreign nuclei are present, in sufficient quantity, the gas-to-particle conversion occurs preferentially on the existing nuclei, i.e., the nucleation is heterogeneous. Available laboratory and atmospheric data indicate that whether homogeneous or heterogeneous nucleation occurs in the atmosphere depends on the relative amount of surface area provided by foreign nuclei. There is evidence that in Los Angeles smog, the nucleation occurs heterogeneously, while in sparsely populated areas the nucleation is homogeneous.
- OSTI ID:
- 5480230
- Journal Information:
- Environ. Sci. Technol.; (United States), Vol. 7:3
- Country of Publication:
- United States
- Language:
- English
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