Removal of nitrogen oxide (NO_x) from urban air by precipitation water was estimated. A result of Principal Component Analysis indicated that, in the daytime, the change of NO_x concentration in the air was mainly influenced by the horizontal wind advection and the change of temperature that is thought to be related to the vertical diffusion. Considering these two effects, the emission of NO_x(R) was computed with a box-model based on surface meteorological data and hourly changes of NOx concentration in South-Kanto area, October 2001. The temporal change of R showed a nearly common shape in no rain days. The washout rates were estimated as 1.0-11.0 ppbv/mm by comparing the shape with that in rain days. To validate this range, the rates were compared with the concentration of nitric acid (NO₃)^- in sampled rains. If the NO₃^- in the rain was produced by the removed NO_x only, the thickness of the atmospheric layer in which NO_x concentration was homogenous (Washout depth) was in the range of 36.7-238 m.

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In order to estimate of dry deposition flux of sulfur dioxide in the atmosphere to the sea water surface, the experiments were performed on the observation tower off the coast of Shirahama and on the pier at the west coast of Awaji Island, for 7days in total from September 2006 to June 2007. Sulfur dioxide fluxes were obtained by the gas concentration gradient method. The average values of SO₂ concentrations were 2.9ppb and 2.7ppb in Shirahama and Awaji Island, respectively. And the total average value of SO₂ concentration was 2.8ppb. The average SO₂ fluxes were-6.7×10^-8g/m²s and-2.8×10^-8g/m²s in Shirahama and Awaji Island, respectively. And the total average value of SO2 flux was-4.8×10^-8g/m²s. The SO₂ gas was deposited to the sea water surface. The average values of dry SO₂ deposition velocities were 0.64cm/s and 0.43cm/s in Shirahama and Awaji Island, respectively. And the total average value of dry SO2 deposition velocity was 0.53cm/s. It was recognized that the dry deposition velocity is positively proportional to wind speed.

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Satellite images on 19-20 April 2000 fortunately observed both of a dust storm and a few frontal clouds near a cold front associated with a midlatitude cyclone in the Gobi Desert. This case is a rare case, which clearly shows the relative position between the dust storm and the frontal cloud system. This study investigates the dust event and the structure of atmospheric disturbances from the Lagrangian viewpoint using satellite images and numerical models. The dust is produced in the cold sector of a frontal system and moves toward the cold front. Near the cold front, the dust flow separates into two main flows both in parallel with the front. One dust flow goes toward the center of the cyclone and the other, toward the opposite direction of the center. Then some of the dust particles reach the center of the cyclone. The vertical distribution of tracer particles is mostly restricted in a mixed layer because of the limited diabatic heating above the layer. Over the sea, dust flow goes over the maritime boundary layer in which air temperature is lower than that of the dust flow. This study clearly shows the dust transport relative to the cold front by the Lagrangian particle analysis.

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Hygroscopic properties of atmospheric aerosol particles at Kagurazaka in Tokyo were investigated in four seasons. A tandem differential mobility analyzer system wasused to measure the dependence of particle size on relative humidity (RH) for monodisperse aerosols with dry mobility diameter of 100nm. In summer, the average of number fraction of growth particles at 65%RH and 70%RH was only 23% and 28%, respectively; however that at 78%RH and 83%RH was 50% and 61%, respectively. In the typical case, number fraction and growth factor in summer suddenly increase over 75-80%RH that were near deliquescence relative humidity of (NH4) 2SO4, NaCl or NaNO3. In autumn, number fraction and growth factor at any relative humidity were almost always smaller than those of other seasons. Number fraction of growth particles at 65%RHwas 41% and 59% in spring and winter, respectively, and similarly that at 70%RH was more than in autumn and summer. Especially in winter, number fraction and growth factor at any relative humidity were large. Number fractions at 70%RH were larger when atmospheric temperatures were low or atmospheric relative humidities were high, which suggests that secondary particles production process from gases relates to existence of particles that grow at low relative humidity.

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Atmospheric O₃, CO and VOCs were measured during spring 2004 at remote site, Hedo, on Okinawa main island. Backward trajectory analysis was employed in order to determine the long-range transport pathways as C (China), K (Korea), J (Japan), and O (Pacific Ocean), for different air masses before reaching to the observatory. The results show clearly the high concentration of these traces gases were arriving from the C and K directions; O₃ of 56.4 and 62.2 ppbv and CO of 240 and 209 ppbv, respectively. The events of high-O₃ low-CO caused O3 monthly averaged mixing ratio in the K higher than of that in the C. The lowest concentration was found in the O. Air mass from the J shows intermediate concentration. VOCs were found to decrease in concentration with an increase in carbon number. This is the signature of the capture of aged air mass. Similar trend of alkanes is the evidence of the clean atmosphere surround the site where there is no nearby emission sources. The main VOCs removal processes are reaction with OH radical. Effect from dilution also takes part in reduction of VOCs concentration. VOCs enhancement ratios obtained from various species were consistent with findings reported from observations in Asian countries. Ratios between i-pentane/n-pentane from the C and K air mass suggested the change in composition of emission arriving from these directions.

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The investigation of airborne behavior of the Japanese cedar pollen 1 allergen Cry j 1 exfoliated from the Ubisch bodies on the pollen surfaces was carried out at the urban, roadside and mountain areas during the pollination seasons of FY 2005-FY 2006 in Saitama, Japan.
The higher concentrations of Cry j 1 were determined in the particle size below 1.1 1.1 m in the urban and mountain area. Furthermore, Cry j 1 was higher in the particle size below 1.1μ m in the roadside than those in the mountain area in the study of FY 2006. It was suggested that the deposited pollens are resuspended from the ground by heavy traffic, and change to fine airborne particles which were observed morphologically by a scanning electron microscope to confirm exfoliated Ubisch bodies of the pollens. Therefore, these pollen allergen particles appear to play a key role in the increasing incidence of asthma in the lower respiratory tract. In our opinions from this study, it is suggested that it is important to determine the size distribution of airborne Japanese cedar pollens and to investigate the chemical, physical and biomedical combination effects on their suspended allergen particulate matters in near future.

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In order to clarify the behavior of ultrafine particles (UFP; less than 0.1 ktm) in lower troposphere, measurement was carried out at a high-rise building in Tokyo during summer and winter of 2005. Samplers of impactor filters (PM_0.1) and cyclones (PM_2.5) were set up at the balconies on the 6th and 55th floors, their carbonaceous (organic carbon (OC), elemental carbon (EC)) and ionic components were analyzed. EC concentrations in PM_0.1 and PM_2.5 at different heights indicated the same variation in summer, respectively. Therefore, it can be thought that EC components were diffused to upper atmosphere by air convective mixing. Even if the variation of PM_2.5 EC concentrations in winter at different heights were remarkably different, EC concentrations in PM_0.1 showed the same variation like in summer. These results suggest that EC from automobile exhaust can reach the upper atmosphere regardless of the season due to its high diffusivity, and it can contribute to the UFP formation in upper atmosphere. In summer, UFP indicated high photochemical reactivity because sulfate concentration increased with OC concentration during day time.

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