Seasonal variation and origin of long-range transported carbonaceous aerosols from East Asia to the East China Sea were investigated. The mass concentrations of elemental carbon (EC), organic carbon (OC), particulate matter smaller than 2.5 μm (PM_2.5) and gaseous CO were measured at the Cape Hedo Atmosphere and Aerosol Monitoring Station (CHAAMS) located on Okinawa, Japan, in 2004-2008. The concentrations of these chemical substances were simultaneously high during the spring and winter (EC: 0.14 - 0.19 μg C/m³, OC: 0.62 - 0.82 μg C/m³, PM_2.5: 14.8 - 19.9 μg/m³, O₃: 43 - 55 ppbv, CO: 183 - 221 ppbv) but low during summer (EC: 0.03 - 0.08 μg C/m³, OC: 0.28 - 0.44 μg C/m³, PM_2.5: 9.85 - 14.8 μg/m³, O₃: 14 - 23 ppbv, CO: 68 - 93 ppbv). It was postulated that pollutants were transported to CHAAMS by migratory high pressures and cold fronts from the Asian continent during the spring and winter, whereas a monsoon transported the oceanic air mass from the Pacific during the summer. The contributions of the carbonaceous aerosol concentrations from China were noticeably higher according to the EC, OC and emissions. The carbonaceous aerosol origin was identified by the OC/EC ratios and the correlation between the EC and OC. The OC/EC ratio was low during the spring and winter (OC/EC: 5.7 - 8.0), but high during the summer (OC/EC: 10.2 - 18.9). These results implied a similar conclusion, i.e., the anthropogenic pollutants were transported to CHAAMS from Asia in the spring and winter, whereas in the summer, a monsoon transported the oceanic clean air mass. A photochemical oxidation reaction was also identified from the high OC/EC ratio. Based on the back trajectories of the air masses, the correlations between the OC/EC showed that the origin of the carbonaceous aerosols in North China (NC) was different from South China (SC). It is also suggested that origin of the carbonaceous aerosols in Japan (JP) and Korea (KR) have an influence on the formations of the secondary organic carbon (SOC) via the reactions of the VOCs, causing the OC fraction to increase.

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Atmospheric particles were collected at two sites, Amami (28°31'N, 129°41'E) and Amakusa (32°21N, 129°59E), which are approximately at the same longitude and 420 km apart in southwestern Japan, on March 18, 2005, during an Asian dust event. The particles were individually analyzed with a scanning electron microscope. Elemental compositions of dust particles at the two sites were compared according to their contents of silicon (Si), aluminum (Al), iron (Fe), potassium (K) and calcium (Ca). Modifications of the particles by mixing with sea salt and aging processes relevant to sulfur chemistry were compared according to their contents of sodium (Na), chlorine (Cl) and sulfur (S). Among Amami's dust particles, Fe and K abundant ones were about 67% and 15%, respectively, while those among Amakusa's were 32% and 8%, indicating that the dust particles at Amami were more abundant in Fe and K than those at Amakusa. The average size of the analyzed particles was larger at Amakusa than at Amami. The particles were significantly changed by the coagulation with sea salt and by surface reactions, resulting in the frequent presence of Na, Cl and S. Weather and backward trajectory analyses revealed that air parcels carrying the particles to the two sites passed different dust source areas in the Asian continent and advectively approached the sites without mutual mixing. Therefore, even within the same dust event, particles at different locations might exhibit different properties due to their origins and experiences in the air.

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Selected polycyclic aromatic hydrocarbons (PAH), nitrated PAH, and quinoid PAH (PAH-quinone) in airborne particles were simultaneously determined at Beijing, China, Osaka, Japan, and Wajima, Japan. The concentration of particle-associated 1,2-benzanthraquinone (benz[a]anthracene-7,12-dione; BAQ), a quinoid PAH, at Beijing was higher than that at Osaka and Wajima by factors of 35 and 200, respectively. Strong correlations between the BAQ and 2-nitropyrene concentrations in the summer and between the BAQ and 1-nitropyrene concentrations in the winter imply that atmospheric secondary reactions and primary emissions significantly contribute to the occurrence of atmospheric BAQ in the summer and winter, respectively. The concentration ratios of BAQ to benz[k]fluoranthene (BkF) in the summer were lower than those in the winter due to the instability of BAQ under sunlight. The BAQ/BkF ratio at Beijing in the Asian dust season was significantly higher than that in the regular spring season, suggesting that the secondary formation of BAQ is promoted by catalytic effects on the Asian dust surface.

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We have developed an air pollution forecast system called VENUS (Visual atmospheric ENvironment Utility System). VENUS automatically calculates the concentrations on the day and the next day of nitrogen dioxide and the photochemical oxidants every night, and produces maps of the concentrations every morning on the web. The system involves the integration of the meteorological model RAMS and the air quality model CMAQ.
The photochemical-oxidants reproducibility of VENUS was verified. The distribution of the concentration and time change in several prefectures were investigated for the high oxidant concentration event that occurred in Japan in May, 2009. The distribution and movement of the high concentration area were well reproduced though the reproducibility of the peak values was quantitatively restrictive. Moreover, the skill scores, such as the correlation coefficient, between the simulation and observations was investigated in May and August of the same year involving the hourly averaged concentration of the photochemical oxidants and its daily top 5% concentration in each prefecture. As a result, the top 5% concentration in particular showed a high correlation coefficient, while the bias and error were low.
Based on these validation results, it was demonstrated that the VENUS has a sufficient accuracy to predict the daily high photochemical-oxidants concentrations in each prefecture in Japan.

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At elevated atmospheric CO₂ concentrations, the soil CH₄ flux may be mediated by plant physiology, including the transpiration rate and water use efficiency. To investigate the effect of elevated CO₂ on atmospheric CH₄ consumption by well-drained forest soil, we measured the soil CH₄ flux at the Free Air CO₂ Enrichment (FACE) site of Hokkaido University during two growing seasons (2008 and 2009). Fumigation with CO₂ began in June 2003, since when the plots have either been exposed to ambient levels or enriched with CO₂ at 130 μL L^-1. We also studied two soil types, brown forest soil and volcanic ash soil, which are widely distributed in northern Japan. The soil CH₄ flux and soil water content were measured simultaneously on four occasions at monthly intervals during each growing season. In both types of soil, the elevated CO₂ plot experienced an approximately 50 % lower soil CH₄ consumption rate than in the ambient CO₂ plot. However, there was no significant difference in soil CH₄ consumption between two soil types. Regardless of the soil type, soil CH₄ consumption was observed at all measurement points in the ambient CO₂ plot, but approximately 13 % of all sampling points in the elevated CO₂ plot experienced net CH₄ production, suggesting that increases in soil moisture influence CH₄ oxidation at elevated CO₂ concentrations.

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The average collection efficiency of gaseous nitric acid (HNO₃(g)) at the Cape Hedo Aerosol and Atmosphere Monitoring Station (CHAAMS), Okinawa, Japan, by an annular denuder method from March 2008 to April 2009 decreased by approximately 20% when compared to that experimentally obtained (~100%). We investigated the causes by which the collection efficiency decreased during the long-term sampling in the marine atmosphere. We experimentally investigated the removal of nitric acid collected from the inner surface of the denuder during the long-term sampling, and it was found that part of the nitric acid collected on the surface of the denuder was removed. However, the experimental result showed that the decrease in the collection efficiency was only 3% on average. We also analyzed the factor in the decreasing collection efficiency using the monitoring data at the CHAAMS. Sea salt particles could be related to the decrease in the collection efficiency. In order to investigate the detailed mechanisms, an intercomparison between the HNO₃(g) concentrations measured by the annular denuder method and a filter pack method by the Acid Deposition Monitoring Network in East Asia was conducted. This result might suggest that the annular denuder method overestimates the HNO₃(g) concentrations and might support the fact that the uptake of the particulate nitrate on the inner surface of the annular denuder causes the decrease in the collection efficiency.

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A new dehumidifier has been developed. The essential feature of the device is the geometry of the coaxial laminar flow, which consists of core and sheath air. The device is designed such that the sample air is introduced as a central core with dry sheath air surrounding this central core. As the sample air passes through the diffusion zone, water molecules travel by diffusion from the central core to the sheath air. At the end of the diffusion, zone the dehumidified central core is withdrawn and then introduced into an SPM measuring instrument.
The performance of the device is as follows.
The outlet/inlet humidity ratio is 0.16 at the sample flow rate of 1L/min and 0.29 at the sample flow rate of 2L/min. At the sample air rate of 2-4L/min, the particle loss is less than 3%.

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