Isao Kanda

Development of outdoor exposure model of traffic-related air pollution for epidemiologic research in Japan.

We developed an exposure estimation model for an epidemiological study on the effect of traffic-related air pollutants on respiratory diseases. The model estimates annual average outdoor concentration of nitrogen oxides (NOx) and elemental carbon (EC). The model is composed of three nested plume dispersion type submodels treating different spatial scales from a few meters to tens of kilometers. The emissions from road traffic was estimated at high spatial resolution along the paths of roads taking into account the effects of individual building shape and traffic signals to secure accuracy near trunk roads where most of the subjects of the epidemiological study resided. Model performance was confirmed by field measurements at permanent local government stations and purpose-built temporary stations; the latter supplemented roadside monitoring points and provided EC concentrations, which are not measured routinely. We infer that EC emissions were underestimated by using the available database because there were significant contributions to EC concentrations from sources that did not emit much NOx. An adjustment concentration yielded good agreement between model estimates and field measurements.

An Urban Atmospheric Diffusion Model for Traffic-Related Emission Based on Mass-Conservation and Advection-Diffusion Equations

This paper proposes an atmospheric diffusion model for traffic-related emission in urban areas within a few hundred meters from relevant roads. The model adopts the mass-conservation (MC) principle for the velocity calculation and the advection-diffusion (AD) equation for the concentration calculation. This MC+AD combination was chosen to achieve fast calculation for complex geometries. To compensate for the inherent deficiencies of MC and AD, as many known properties possible of turbulent boundary-layer flow over obstacles are incorporated into the MC calculation, and the diffusivity in AD is derived from the velocity spectrum as a function of distance from the emission source. The model is evaluated against wind-tunnel experiments ranging from point-source emission in uniform urban canopy to along-road emission in real city geometries. The model performs well in relatively simple configurations, but the performance deteriorates considerably as the complexity increases. However, in real city geometries, the model exhibits distinctly better performance in terms of statistical indices than a conventional Gaussian-plume model that neglects the effect of individual buildings. The model is therefore a viable option for environmental assessment.

Sidewalk pollution flows caused by vehicular traffic place children at a higher acute exposure risk

The objective of this work is to study the immediate transport flows of PM2.5 diesel exhaust emissions on a city sidewalk. Under calm conditions largest direct exhaust PM2.5 diesel concentrations tend to accumulate at two preferred heights: higher ones at 200–225 cm due to truck and buses aerodynamics, and lower ones at 130–160 cm due to light vehicles. Obtained flows indicate that exhaust emissions are transported to these heights via vortices generated by vehicular traffic. The lower height vortices transporting PM2.5 direct diesel emissions place children aged between 7 and 15 at a higher acute exposure risk due to their stature. Also, the hourly averaged PM2.5 concentrations tend to accumulate nearer to the roadside. This information was obtained using a specially designed electromechanical near-surface atmospheric profiler equipped with a PM2.5 measurement instrument, a thermistor and a sonic anemometer installed on a sidewalk. Using signal analysis techniques, coherent flows of direct PM2.5 emissions and thermal information were obtained. The proposed methodology can be used to evaluate before and after urban interventions, obtain full-scale sidewalk data for exposure studies and provides criteria on where to place sidewalk measurement instruments.