NUMERICAL STUDY ON DYNAMICS EFFECT AND RADIATION TRANSFER CHARACTERISTICS OF ATMOSPHERIC PARTICLE BY MONTE CARLO METHOD

During the burst reinforcement period of fog, air pollution and low visibility are very serious, which is closely related to the turbulence characteristics of the atmospheric boundary layer, the dynamics and scattering properties of suspended particles. Based on the particle population balance equation and Mie theory, a program is self-developed. The computed particle size distribution function and particle scattering property are consistent with the experimental and theoretical data, which verify the correctness of models and numerical method. Numerical study on the mechanism of droplet spectrum broadening, visibility reducing during the fog burst-enhanced phase is conducted, and the e ects of turbulent transport and particle local aggregation on the coagulation of particles are discussed. Combining with particles scattering nature, the influence of particle turbulent dissipation rates on the radial relative velocity and the transmissivity of system in the fog development are analyzed numerically. Relation between the radial relative velocity, the transmissivity of system and the particle size are discussed. The computed results suggest that the radial relative velocity of particles increases slowly and then increases rapidly with the rise of turbulent dissipation rate. At 1 000 s, the turbulent dissipation rate is 1.0×10^-2m²/s³, and the dimensionless radial relative velocity of particle is 0.096 9. For 0.6 μm wavelength of visible light, the transmissivity of fog is 0.47. Furthermore, aerosols are coagulated with fog droplets in the development region of fog to decrease atmosphere visibility, which radiation properties are di erent from pure droplets.