A new statistical approach for the determination and investigation of modes of nanoparticle aerosols in the presence of strong turbulent mixing is developed. It is demonstrated that the conventional mechanisms of transformation of aerosol nanoparticles, such as nucleation, coagulation, evaporation, and dispersion fail to consistently explain numerous effects in a complex pattern of evolution of a combustion aerosol near a busy road. Therefore, a new mechanism of such evolution-thermal fragmentation of nanoparticles-is introduced and justified. As a result, a comprehensive pattern of mode evolution is presented, analysed and interpreted on the basis of existence of primary solid carbon/graphite particles covered with volatile organic compounds. It is shown that a feasible mechanism for particle fragmentation is based on the loss of bonding due to evaporation of volatile molecules from the surface of nanoparticles. As a result, an interpretation of the major experimentally observed effects of mode evolution is presented. (c) 2004 Elsevier Ltd. All rights reserved.