Koji Kitabayashi

Comparative study on estimation methods for NOx emissions from a roadway

Abstract In order to estimate NOx concentration at road side areas, it is necessary to determine the NOx emissions from the automobile passing a road. There are two methods for estimation of NOx emission. One is calculated by the emission factor of automobile, driving mode and traffic volume. Another is a method based on the relation between NOx and tracer gas concentration of diffusion experiment. First, diffusion experiments by air tracer were conducted. They were carried out at two areas, one of which was an open area and the other was a highly-built-up area. In the experiment, traffic volume, NOx and tracer gas concentrations were measured simultaneously. However, the result obtained at the former area was used for this analysis. The NOx emission rate of the automobile was calculated from the data of traffic survey and tracer gas experiments and both results were compared. Three methods for estimation of NOx emission rate from traffic survey were employed in this study. From these results, it can be confirmed that both results are in agreement and well correlated, so these estimation methods are considered to be appropriate.

Development of numerical model for dispersion over complicated terrain in the convective boundary layer

Complicated terrain and atmospheric stability are important factors in the predicting the dispersion of air pollutants. The aim of our study is to develop practical dispersion model for unstable conditions for regulatory use. The numerical model we adopted was a combination of the potential flow model and Lagrangian stochastic dispersion model. In this model, time-mean flow field is solved by the potential flow model and concentration field is calculated by Lagrangian stochastic model by using the flow field from potential model. Wind tunnel experiments simulating gas dispersion in the convective boundary layer were also done. The data sets of turbulent properties and concentrations obtained in the wind tunnel were used for the modification of dispersion model and model validation. Based on the developed model, user-friendly software applicable to dispersion over complicated terrain was also developed.