Annual changes of the pH of upstream river and lake water in the mountainous region in central Japan was investigated by using 32-years (1972-2003) worth of records. Monthly pH at 27 water quality monitoring points (22 points along 17 rivers and 5 in lakes) with negligible anthropogenic pollution effects and precipitation pH at 21 air pollution sampling sites from 1972 to 2003 were analyzed statistically and the characteristics of long-term trends and distribution, along with their relationship, were investigated.
Acid rain monitoring data and atmospheric deposit gauge data indicated that precipitation pH in Nagano Prefecture ranged from 4.8 to 5.3 for the years 1972-2003. Annual mean precipitation pH levels were lower in the northeastern part of Nagano Prefecture, since it was easily affected by the long-range transport of acidic pollutants from the Tokyo metropolitan area and the Asian Continent. The central part of Nagano Prefecture, on the other hand, was not affected as much, with the annual mean precipitation pH level being higher. Seasonal changes of precipitation pH in Nagano Prefecture were attributed to the emission of acidic pollutants in local and neighboring areas, transport of pollutants from extensive emission source areas in the warm season, transboundary transport of acidic pollutants from the Continent in wintertime, and transport of Kosa (Asian dust) in springtime.
In the past 30 years, pH values of upstream river and lake water showed significant decreases (level of significance α= 0.01: 12points, 0.05: 3points) at 15 out of the 27 points. The decreasing pH trend of Hime-kawa, Aokiko, Takase-gawa, Kizaki-ko, Azusa-gawa and Matsu-kawa, where watershed bedrock was made of acidic rock such as granite and rhyolite, was confirmed to be ΔpH= 0.3-0.7 for the 30 years, even after the previous reports (Kurita et al., 1990, 1993). In addition, Nakatsuna-ko, Narai-gawa, Yomase-gawa, Koshibu-gawa Nakatsu-gawa, Tagawa and Susobana gawa also showed decreasing pH tendencies, which had not been reported in the previous papers. The estimated pH decreases of these rivers over the 30 years were 0.3-0.8. In most of these rivers the long-term decreases of pH values were closely related to alkalinity (HCO₃^- concentration) data. This suggests that the long-term pH decreases were caused by acid rain. Of the 15 points where the decreases of freshwater pH were significant, the lowest pH= 6.3 in the year of 2003 was observed in Yomase-gawa. The next lowest pH points were Kizaki-ko (bottom), Nakatsu-gawa, Nakatuna-ko, Aoki-ko, and Takase-gawa, the pH being in the range of 6.4-6.8. In the case of Yomase-gawa, the low concentration of HCO₃^- was due to the inflow of hot spring water with low alkalinity, which reduced the acid neutralization capacity; thus causing a remarkable decline of the river pH in the early snow melting season.
These findings suggest that, in the upstream areas of the central mountainous region, pH values of a number of rivers and lakes with low acid neutralization capacity have been decreasing over the years, and that the decreasing pH areas are extending gradually from areas that lie over acidic bedrock to other areas.

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A wind tunnel study was conducted to investigate the dispersion of leaked gas from a hydrogen refueling station using a fast-response concentration detector. The station model used in the study was that of a gaseous hydrogen refueling station with onsite hydrogen production. The production capacity was 300 Nm³/hour and the storage vessels were compressed to 40 MPa. The tracer gas, ethane, was mixed with helium gas for buoyancy, and then was released from the compressed storage unit model. For a large leak from a 5mm hole for a 20s gas release time, the gas spread over a wide area downwind and upward. The 4% peak concentration length (L_peak: the longitudinal distance from the gas source to the boundary of a peak concentration region) extended 24 meters away from the source, the storage building. For a medium leak from a 1mm pinhole, the 4%L_peak remained onsite at a distance approximately 4m downwind of the source. For a small leak from a 0.2mm pinhole, the 4% L_peak did not appear clearly downwind from the source. When the gas release time changed from 20s to 3s for the large leak, the 4% L_peak decreased from more than 24m to 7m. The results suggest that fast leak detection and fast shutdown are very important to minimize risk. A reduction of concentration in the early diffusion stages near the source reduces the 4% L_peak distance downwind of the source. This result suggests the importance of the ventilation system design in the source storage building.

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The dry deposition of ammoniacal nitrogen (NH_x) on managed turf grassland in Tsukuba, central Japan, was investigated from August 14, 2004 to February 28, 2005. A filer-pack method was employed to measure the weekly mean concentrations of NH₃ and particulate NH⁴⁺ in the atmosphere. An inferential method was applied to estimate the dry deposition velocities of NH₃ and particulate NH⁴⁺, which included the effects of NH₃ emission through plant stomata and surface wetness on the dry deposition velocity of NH₃. The dry deposition of NH_x was calculated by multiplying their atmospheric concentrations by their deposition velocities. As the mean values for NH₃ and particulate NH ⁴⁺, the atmospheric concentrations were 150 and 89 nmol m^-3, the dry deposition velocities were 0.66 and 0.061 cm s^-2, and the dry depositions were 80 and 4 μmol m^-2, d^-1, respectively. The atmospheric concentrations of NH_x were considered to be a typical condition in rural areas. The estimated dry deposition velocity of NH₃ was at the lower limit among the existing studies. The effect of NH₃ emission from plant stomata averagely decreased the mean dry deposition velocity of NH₃ in 0.013 cm s^-1 (2.0 %). On the other hand, the effect of surface wetness averagely increased that in 0.042 cm s^-1 (6.4 %). The degree of annual dry deposition of NH_x converted from the daily means was similar to the wet deposition of NH⁴⁺ in Japan, which showed that dry deposition strongly contributes to the atmospheric deposition of NH_x. The dry deposition velocity of NHx increases in vegetation such as natural grasslands and forests with a larger aerodynamic roughness. Therefore, the contribution of dry deposition to atmospheric deposition of NH_x is likely to enlarge in these natural vegetations.

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To study the flow and distribution of air pollution around a heavily-trafficked urban roadway we conducted wind tunnel studies using a 1: 100 large-scale model of the actual built-up area in Ikegami-Shinmachi, Kawasaki-shi, Kanagawa. We measured the flow around the main road using the PTV (particle image velocimetry) technique, and measured the concentration distribution in the surrounding areas with a 12-channel hydrocarbon analyzer.
We then examined the influence of some countermeasures against the high concentrations found along the urban roadway. 1) The sound insulating wall installed along the sidewalk had little influence. 2) Diverting ground-level traffic to the elevated roadway was effective. 3) Exhaust fans, which take the polluted air from the roadway and direct it upward, were effective. 4) The adoption of upward-facing exhaust pipes by large-sized diesel motor vehicles was effective.

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[in Japanese]

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