The Regional Atmospheric Modeling System, RAMS, was used to perform an annual simulation for the Asia region in order to determine the meteorological conditions of the CTM (Chemical Transport Model). The model of the Asian domain was subdivided into 13 sub-regions and the averaged meteorological fields in each region were compared. At first, it was found that the observed and simulated time variations of meteorological parameters for April 2001 showed good agreement and most of the regions showed high statistical scores. The simulated total precipitation maps explained characteristics of the total precipitation distribution for each season well when compared with the CMAP observation field. It was found that the simulated five day accumulated precipitation was underestimated for weak precipitation events of less than 10mm. The simulated monthly accumulated precipitation has a bias of about 20-40% during the summer and autumn in Japanese regions. The simulation results showed that a ratio of precipitation by cumulus contributed to 24-36% of the total precipitation amounts in the north regions in China and Korea for spring and summer, and this fact suggests that the treatment of convective precipitation within the CTM framework would have a strong influence for the concentration field.

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Trends of concentrations of suspended particle matter (SPM) from FY 1996 to in urban areas of the Kanto district, such as Tokyo, Kanagawa and Saitama prefectures were analyzed in the context of policies and regulations adopted for emission control, especially to separate the effects of regulations for automobiles and incinerators.
The Contribution of primary particles from automobiles to the ambient monitoring stations is estimated by assuming that it is in proportion to the difference of concentration measured at all the road-side monitoring stations and ambient monitoring stations in a prefecture. As a result, the contribution of automobiles to SPM concentration at ambient monitoring stations appears to have decreased remarkably over a nine year period in these areas.
The contribution of NOx (= NO+ NO₂) by automobiles, however, has slightly decreased during the same period.
The contribution of incinerators to SPM concentration was estimated next, since the regulations for the emission of dioxins started in 2000, which could have affected SPM concentrations. Since the concentrationsof dioxins were in good correlation with SPM concentrations at ambient monitoring stations, with the subtraction of contribution of the primary particles from automobiles, the linear regression between those two kinds of substances was assumed. The results indicated the regulations for dioxins appeared to contribute great deal to the decrease in SPM concentrations. The contribution of the primary particles from these two kinds of emission sources to the total SPM concentration has decreased, thus the secondary particles observed in the summer season become more noticeable.

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OH radical reactivity in the semi-urban atmosphere was measured by a laser flash pump and the probe technique which was developed by our group. The observation OH reactivity during the hole of the year was carried out as well as ancillary measurements of VOCs (Volatile Organic Compounds), NOx, and CO. We defined the oxidant potential, Φ, which tells the number of accumulated peroxy radicals through the radical propagation cycle from a single OH radical. We compared the Φ value derived from the observational results of the OH reactivity measurements with those estimated by the ancillary measurements of VOCs. Under a higher NOx regime, usually higher than 30 ppb, there is no difference between them. However, for cases of cleaner conditions there is a huge difference between the measured and calculated Φ values since the radical propagation cycle will produce large non-linear changes in the production of ozone. We successfully applied the Φ value to the interpretation of the weekend effect of ozone concentration observed on our campus.

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Measurements of O₃, NO_x and SO₂ concentrations were performedat Bijodaira (altitude 977m), on the westernn slope of Mt. Tateyama, in the summer and autumn of 2004 and 2005. A clear diurnal variation of O₃, reaching amaximum during the afternoon, was observed in the summer and early autumn. No clear diurnal variation was seen in November. However, NO _x concentration was higher in the daytime than in the nighttime both in the summer and in the autumn. The difference in diurnal variation of O₃ may be due to the photochemical formation of O₃ during the summer and autumn. High concentrations of SO ₂ were sometimes observed in November. The backward trajectory analysis showed that the high concentrations of SO₂ at Bijodaira originated from the pollutant regions of the Asian continent.

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The air concentrations and concentration gradients of nitrous acid (HONO) and nitric acid (HNO₃) on managed turf grasslands in Tsukuba, central Japan, were investigated from June 29, 2004 to January 11, 2005. A filerpack method was used to measure the weekly air concentrations. As the mean values for warm and cold seasons, the concentration of HONO was 0.86 and 1.2 ppb (v/v), respectively, and that of HNO₃ was 1.0 and 0.23 ppb, respectively. The HONO concentration was similar to HNO₃. As the mean values for warm and cold seasons, the concentration gradient of HONO between the heights of 4 and 2 m was-0.012 and-0.027 ppb m^-1, respectively, and that of HNO₃ was 0.10 and 0.008ppb m^-1, respectively. A negative gradient indicates an upward flux. The negative gradients of HONO showed that the HONO formation occurred at the surface and the emission fluxes exceeded the deposition fluxes. The surface HONO production was attributed to the heterogeneous formation of HONO from nitrogen dioxide in between the gas-solid phases. The surface-atmosphere exchange of HONO needs to be quantified as a net flux. Thus, the surface emission of HONO should be involved in estimating a HONO deposition velocity.

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[in Japanese]

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