This paper describes the first survey on the sources of primary particles and the precursory gases of secondary particles that cause severe Suspended Particulate Matter (SPM) pollution in the Kanto Plain, Japan, in early winter. The emissions of elemental carbon (EC), primary organic carbon (OC), primary sulfate (SO₄^2-), hydrogen chloride (HCl), ammonia (NH₃), nitrogen oxides (NO_x), sulfur dioxide (SO₂), and non-methane hydrocarbons (NMHC_s) were estimated in an area of 220×230 km (over the Kanto Plain) in 1994. The emission factors for EC and OC from mobile sources were estimated based on road-side measurements of emissions from automobiles. The emission source model for HCl was developed by assembling emission data from municipal waste incineration plants and industrial waste incineration plants. Livestock, fertilizer use, NO reduction facilities at power plants and municipal waste incineration plants, automobiles, human perspiration, and sewage treatment plants are all considered as sources of NH₃. Emissions of NO_x, SO₂, and NMHC_s were compiled based on a previously reported data set. The estimated total emission of elemental carbon in the Kanto Plain was-4 times that of the model region of South Coast Air Basin, USA, in the winter of 1980. Total emission of HCl in the Kanto Plain was estimated to be comparable to the emission of HCl from waste incineration in the U. K. in 1984. Estimated total emission of NH₃ may contain significant errors owing to the uncertainties in the emission factors adopted.

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In order to determine the distribution of Abies firma (Momi fir) decline in mountains of western Tokyo, 107 sites (618 specimens) were studied from 1992 to 1993 to evaliate the decline. Total decline index which summed up variables of twig death, crown density, crown form and vigorousness was effective as a criterion for the survey. The percentage of declining trees, whose rank was 2 or more regasding twig death and crown density, was 45.2%, and 45.6% respectively. The decline of Abies firma was unrelated to geographical factors, that is, slope classification and valley density. On the other hand, there was a correlation between the decline and longitude and latitude of the sites, indicating a decline in the southeastern area and slightly damaged area in the northwestern mountains of Tokyo. But there was severe fir decline in a part of the valley located in the northwestern area. Concerning altitude, the decline was severe in low regions of 250 m or less in altitude, and healthy at high altitudes. However, even at altitudes of 750 m or more a slight decline of 57.9% was observed.

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The dry deposition of sulfur was estimated using an inferential method based on the results of one-year measurements at a Japanese cedar (Cryptomeria japonica) forest located in Gumma Prefecture. From the results of estimation, the influence of canopy wetness on the dry deposition of SO² was evaluated. During the observation period, from October 1997 through September 1998, the wetting time period amounted to 17% of the total cold season (October to March) and 60% of the total warm season (April to September). The deposition velocity for SO₂ was estimated under the assumption that cuticle resistance (R_cut) is negligible when the canopy is wet. Using this assumption, the deposition velocities for SO₂ estimated using a calculation scheme developed in the United States were about twice as high in the cold season and were about three times higher in the warm season than those estimated under the assumption that R_cut is constant during the entire observation period. The inferential estimate of dry deposition flux for sulfur was 11.1 mmol m^-2 yr^-1 under the assumption that R_cut for SO₂ is negligible for a wet canopy. This value agreed fairly well with the net throughfall flux for sulfur (12.4 mmol m^-2 yr^-1). Therefore, the influence of canopy wetness due to the humid Japanese climate, is an important factor governing SO₂ dry deposition to forests.

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To evaluate the temporal variation of atmospheric deposition of H⁺, three-year field measurements were conducted during the period from April 1997 through March 2000 in a Japanese cedar (Cryptomeria japonica) forest, located in Gunma Prefecture, Japan. On the basis of the meteorological and atmospheric concentration data, the dry deposition of SO₂, HNO₃, NO₂ and HC1 were estimated using an inferential method. The estimated annual dry deposition of H⁺ ranged from 61 mmol m^-2 yr^-1 to 83 mmol m^-2 yr^-1. Compared with the uncertainty of estimates, the annual variation in deposition of H⁺ was not significant. The observed annual wet deposition of H⁺ ranged from 28 mmol m^-2 yr^-1 to 43 mmol m^-2 yr^-1. Therefore, approximately twice as much H⁺ was constantly loaded to the studied forest by dry deposition than by wet deposition. The dry deposition of H⁺ in the warm season was slightly greater than that in the cold season. The magnitude of the seasonal variation of dry deposition was relatively smaller than that of wet deposition of H⁺ However, the contribution of each gas to the dry deposition of H⁺ indicated a clear seasonal change. Although HCl was the dominant contributor in the cold season, the contribution of HNO₃ and SO₂ increased in summer.

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Diesel engine exhausts contain high levels of toxic gases and soot. Lowering thesulfur content in fuel is expected to reduce SO₂ concentration and particle acidity in exhaust. We conducted in vitro and in vivo tests to examine the health effects of lowsulfur light oil (LSLO) on rats. Marked reductions of SO₂, SO₄^2- and particle mass concentrations in LSLO exhausts were confirmed. The amounts of polycyclic aromatic hydrocarbons (PAH) and nitro-PAH in diesel exhaust particles (DEP) were variable. Mutagenicity and 8-OH-deoxyguanosine formation were slightly lower with LSLO than high-sulfur light oil (HSLO) particles. However, inhalation experiments on rats exposed to the same mass concentration of particles demonstrated a significantly higher frequency of lung tumors and higher lung burden in LSLO compared to HSLO exhaust. Intratracheal instillation using three doses of DEP also showed higher dose-related tumorigenesis with LSLO, correlating with the degree of particle retention in the lung. Distribution of particle sizes showed a higher proportion of nanoparticles in LSLO than in HSLO DEP. Lowering sulfur content in diesel fuel, thus, can significantly decrease the mass concentration and acidity of soot, but enhance tumorigenicity for its same mass concentration. Further efforts to eliminate particles from diesel exhaust are thought to be necessary.

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[in Japanese]

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