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A simple semianalytical model of dispersion of nanoparticle aerosols from a busy road in the presence of intensive particle fragmentation is developed. In particular, it is predicted that the total number concentration may be characterized by a significant maximum at an optimal distance from the road. Simple analytical existence conditions of such a maximum are derived. Applicability conditions for the model and the effect of turbulent diffusion and dry deposition of nanoparticles on the theoretical predictions are also discussed. As a result of the comparison of the theoretical predictions with the experimental results on the total number concentration as a function of distance from the road, the typical fragmentation rate coefficient has been determined as ≈0.086 s-1, with an estimated error of ∼30%. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we report the results of the detailed monitoring and analysis of combustion emissions from fast moving diesel trains. A new highly efficient monitoring methodology is proposed based on the measurements of the total number concentration (TNC) of combustion aerosols at a fixed point (on a bridge overpassing the railway) inside the violently mixing zone created by a fast moving train. Applicability conditions for the proposed methodology are presented, discussed and linked to the formation of the stable and uniform mixing zone. In particular, it is demonstrated that if such a mixing zone is formed, the monitoring results are highly consistent, repeatable (with typically negligible statistical errors and dispersion), stable with respect to the external atmospheric turbulence and result in an unusual pattern of the aerosol evolution with two or three distinct TNC maximums. It is also shown that the stability and uniformity of the created mixing zone (as well as the repeatability of the monitoring results) increase with increasing length of the train (with an estimated critical train length of ~10 carriages, at the speed of ~150km/h). The analysis of the obtained evolutionary dependencies of aerosol TNC suggests that the major possible mechanisms responsible for the formation of the distinct concentration maximums are condensation (the second maximum) and thermal fragmentation of solid nanoparticle aggregates (third maximum). The obtained results and the new methodology will be important for monitoring and analysis of combustion emissions from fast moving trains, and for the determination of the impact of rail networks on the atmospheric environment and human exposure to combustion emissions. [ABSTRACT FROM AUTHOR]