We conducted wind tunnel experiments using a simplified 2-dimensional model of an existing urban area to study the relationships between the concentrations of pollutants on and around the main road and the structure of the road and the atmospheric stability.
In the study area, a fence covered with thick ivy has been installed between the piers of an elevated roadway in an effort to reduce the localized high concentrations of air pollution along the roadway. However, by obstructing natural ventilation beneath the elevated roadway, it seems that the fence actually increases the concentration. We closely measured the concentration distribution of pollutants in and around the main road, examined the effect of the fence, and discussed ways to reduce the localized high concentrations in and around the main road.
The main results are as follows:
1) Within the range of this experiment there was no pronounced tendency for high concentrations to occur on the ground-level road beneath the elevated roadway when the air pollutants were discharged on the elevated roadway.
2) Concentration distribution changed dramatically with the structure of the main road (existence of the elevated roadway, existence of the fence, etc.). However, in the surrounding area, the differences in concentration due to the structure of the main road diminished as the distance from the main road increased.
3) Atmospheric stability has a large influence on roadside concentration. Large differences in concentration under neutral and stably stratified conditions were also seen in the surrounding area; these differences in concentration increased with distance from the main road.
4) The fence may obstruct the natural ventilation beneath the elevated roadway, thereby increasing the area of localized high concentration.
5) Ground-level concentration can be reduced by directing some of the traffic on the ground-level road to the elevated roadway.

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The rate of decrease of 13 polycyclic aromatic hydrocarbons (PAHs) in atmospheric aerosols (fine particulate matter; particle diameter<7.0μm and coarse particulate matter; particle diameter>7.0μm) and deposited particulate matter was measured. The atmospheric aerosols and deposited particulate matter were collected and the decrease of the PAHs contents was measured over one year at the site in a suburban area. The rate of decrease (k) of PAHs was determined from the first-order law for each collected particulate matter and kmed was defined as the median value of all PAHs for each sampling. The K_med value was 0.3d^-1 at maximum. For the comparisons of different particulate matters, the kmed values were largest for fine particulate matters (0.1-0.3d^-1). The K_med values were larger in summer for fine particulate matters than those in other seasons, while those of coarse and deposited particulate matters showed less seasonal variations. For deposited particulate matters, the K_med values were higher in winter and were contrary to the expectations. For fine particulate matter, the seasonal variation of the PAHs contents was strongly related to those of the k values. This study showed the importance of the content pattern changes of PAHs by decomposition in elucidating the behavior of PAHs in atmospheric environments.

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The major ion species (Na⁺, nss-S0₄^2-, NO₃^-, NH₄⁺, nss-Ca²⁺) in precipitation, which was collected at the top (620m a.s.l.) and foot (47m a.s.l.) of the Yahiko-Kakuda mountains area in Niigata, Japan, were measured. The washout rates of the ion species between the top and foot of the mountain were calculated for non-snowy and snowy seasons from the differences in deposition fluxes between the two sites. The atmospheric concentrations of gas and aerosols were also measured at the top of the mountain, and the washout ratios (W, W=C_{precipitation}/C_air in which C_{precipitation} and Cair are the ion concentrations (mg/kg) in precipitation and in the air (mg/kg) at ground level, respectively) were calculated for the two seasons separately, in order to discover the precipitation scavenging above the top of the mountain.
It was estimated that about 30% of Na+ in precipitation collected at the foot of the mountain is incorporated to precipitation between the top and foot of the mountain. Little amount of nss-SO₄^2- is incorporated between the two sites both in non-snowy and snowy seasons, in contrast a large amount of nss-Ca²⁺ is incorporated in both the seasons. The washout ratios for Na⁺, nss-SO^42-, and NH₄⁺ in precipitation collected at the top of the mountain showed higher vales in the snowy season than the non-snowy season, while there was little difference in those for nss-Ca²⁺ and NO₃^- between the two seasons.

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