Although the influences of colloidal materials on radionuclide transport in geological media are pointed out, their behaviors in natural environment have not yet been well elucidated and therefore their influences on the geologic disposal of high-level radioactive waste (HLW) are not fully estimated quantitatively. This paper reveiwed the studies on natural colloids, especially focused on inorganic, organic and biological colloids, and discussed the future works to be carried out. Much attention should be paid to the sampling and analysis. Excellent techniques for in-situ observation, concentration without changing the state of colloid, standard procedure for analysis, are necessary to be developed. More research studies on the behaviors of colloids are required in not only far- and near-fields but also items on effects of the environments and its evolution.

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Aerosol particles exist abundantly in the ambient atmosphere, where their diameters range from 〜10nm to > 10μm. The atmospheric particles directly reflect or absorb solar radiation, cooling or warming the earth surface. If the aerosol are enriched with ammonium sulfate and organic compounds, they scatter the radiation back to the space because of their white nature. In contrast, if the particles are enriched with black carbon, they absorb the radiation and warm the atmosphere. The direct effect of the aerosols on the radiation, therefore, largely depends on their chemical composition. Further, aerosols can act as cloud condensation nuclei (CCN) to form clouds, which indirectly control the radiation balance on the earth surface. This indirect effect of aerosols is also controlled by the chemical composition of aerosols and their hygroscopic properties. Both direct and indirect effects of atmospheric aerosols are significantly influenced by their chemical composition. Although these effects on the radiation are large enough to cancel out the warming effects of greenhouse gases emitted by human activities (IPCC, 2001; 2007), there are significant uncertainties in the estimates of the direct/indirect effects on the earth surface. The uncertainties are mainly caused from the incomplete understanding of chemical composition, spatial distributions and physico/chemical properties of aerosols in the atmosphere. Atmospheric aerosol particles contain inorganic and organic pollutants (e.g., sulfate, organic acids, etc.) that cause adverse effect on plants, animals as well as human health on a regional and global scale. Those chemical species are primarily emitted from the various sources and/or secondarily produced in the atmosphere by photochemical exidation of precursor compounds. For the last two decades, economical growth and industrial development have been significantly enhanced in the East Asian countries, especially in China. Consequently, atmospheric emissions of aerosol particles and their precursors (SO_x, NO_x, volatile organic compounds, etc.) have seriously increased in East Asia as a result of increased usage of fossil fuels (Akimoto, 2003). In addition to the increased sulfur emissions, a significant increase in the concentration of nitrogen oxides has been observed in the coastal China by the satellite observation from the space (Richter et al., 2005). In the western Pacific region, important international programs on atmospheric aerosols have been conducted for the past several years, including ACE-Asia project (Aerosol Characterization Experiment in Asian Pacific Region) (e.g., Huebert et al., 2003). Many Japanese scientists have joined to those programs and contributed to a progress in the aerosol chemistry in East Asia. In this special issue, we collected 6 papers focused on the Special Session on Geochemisty of Aerosols and Related Gases in the East Asia and Pacific Ocean region (7 oral and 10 poster presentations), which was held at the annual meeting of Geochemical Society of Japan (October 13-15, 2006, Tokyo). Six papers presented in this issue cover several topics on the water-soluble ions in the aerosols from Chinese mega-cities, semi-volatile aldehydes in Tokyo, organic tracers in Jeju Island, South Korea and Cape Hedo in Okinawa Island, long-range atmospheric transport of Chinese dusts over western Japan, and chemical composition of sea fogs as a scavenger of atmospheric particles over the western North Pacific. Although these topics are few examples of the aerosol studies that have been conducted in East Asia and the western North Pacific, these papers should be helpful to understand the current research subjects of aerosols and most recent outcomes from the aerosol programs in East Asia. We wish that this Special Issue of Geochemistry could act as useful media for the aerosol community and the new comers to this research field of atmospheric chemistry.

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A yearlong field observation of water-soluble ionic composition in TSP and PM_2.5 was carried out in Xi'an and Beijing, China from September 2005 to August 2006 with the aim of characterizing the atmosphere in Xi'an. Concentraions of water-soluble ions (Na⁺, NH₄, K⁺, Mg²⁺, Ca²⁺, F^-, Cl^-, NO₃^-, and SO₄^2-) were determined by ion chromatography for approximately 250 samples. The concentrations of the sum of 9 ions were TSP: 81.8±64.8μg/m³ (n=80), PM_2.5: 46.0±31.7μg/m³ (n=68) in Xi'an, and TSP: 60.8±27.2μg/m³ (n=44), PM_2.5: 33.6±20.1μg/m³ (n=45) in Beijing. The concentration of each ion in Xi'an was 1-3 times higher than that in Beijing. SO₄^2- was the dominant ionic component of the aerosols in both cities. SO₄^2- concentrations in PM_2.5 in both cities in summer was 1.3-1.9 times higher than those in winter while SO₂ concentrations in both cities in winter were 4-8 times higher than those in summer. These facts suggest that sulfate concentrations in both cities were not mainly controlled by SO₂ concentration but the intensity of gas- or liquid-phase reaction in the atmosphere.

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Diurnal variation of semi-volatile carbonyl compounds (glycolaldehyde, hydroxyacetone, glyoxal and methylglyoxal) were studied during July and August 2004 in urban Tokyo using an annular denuder sampling system and gas chromatography (GC). The carbonyls were collected on a deuder tube, whose surface was coated with O-Benzylhydroxylamine (BHA) and XAD-7 as collection reagent. The compounds were measured using a capillary GC after two-step derivatization processes with BHA and N, O-bis (trimethylsilyl) trifluoroacetamide (BSTFA). Gaseous concentration of semi-volatile carbonyl compounds showed a rapid increase in the morning and reached a maximum around noontime. Then, the concentrations significantly decreased in the evening and reached a minimum at midnight. The averaged concentrations were 1548 ng m^-3 for glycolaldehyde, 797 ng m^-3 for methylglyoxal, 406 ng m^-3 for glyoxal, and 362 ng m^-3 for hydroxyacetone. We found that these carbonyl concentrations were 2-21 times higher than those reported in the forest area in Japan. Good correlations were found among concentrations of the carbonyl compounds. Total concentrations of the compounds also showed a good correlation with oxidant (mostly ozone) and solar radiation, suggesting that secondary photochemical productions of carbonyl compounds are important.

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In an attempt to elucidate sources of combustion to EC and other incomplete combustion products, we investigated seasonal variations of PAHs and molecular markers for biomass burning (levoglucosan: LG, dehydroabietic acid: DH and retene) in fine particulate mountain aerosols at the 1100 m declive of Mt. Halla, Jeju Island, Korea. PAHs observed at the site (sum of 3-6 ring parental PAHs: 0.05-7.8 ng/m³) were mostly of combustion origin and showed an intense signal in winter and several minor maxima in summer. Observations of LG (0.3-840 ng/m³) and resin diterpenoid markers (DHA: 0.1-127 ng/m³, retene:2-80 pg/m³) throughout the year evidenced biomass to be a significant source of combustion to the study site. Combination of PAHs isomer pair ratios and biomass-burning tracers revealed that biomass-burning contributions intermittently overwhelmed that from fossil fuel combustion. The backward trajectory analyses showed that the intense signals of LG/PAHs ratio in fall-winter were dominated by airmass from island areas while those in summer were ascribed to selective loss of PAHs by photochemical process. On the other hand, DHA and retene spikes in summer were judged to be from local Pinaceae combustion sources. Strong influence of westerly for samples with intense signal of biomass burning (i.e., LG, LG/PAH ratio and PAHs isomer pair ratios) indicates that biomass is an important source of combustions in the inland of East Asia and its pyrolytic products are available for long-range transport in winter.

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To study long-range transport of organic aerosols from East Asian countries to the East China Sea, 3- to 7-ring parental polycyclic aromatic hydrocarbons (PAHs) in aerosols collected at Cape Hedo, Okinawa, Japan (128.3°E, 26.9°N) during 2005-2006 were analyzed by high performance liquid chromatography. The total PAH concentrations were 0.00-16.0 (av. 1.22) ng m^-3 during the entire period. The seasonal average of total PAH concentration increased between winter and spring and decreased in summer. It is interpreted that the pollutants are transported to Cape Hedo by the monsoons from the Asian Continent between winter and spring, whereas oceanic air mass is transported by the monsoons from the Pacific in summer. The benzo[a]pyrene to benzo[e]pyrene ratios were 0.23-0.98 (av. 0.48) in winter and were lower than that measured in East Asian cities, showing that PAHs observed at Cape Hedo are aged by the photochemical reactions proceeding during long-range transport. The average total PAH level measured at Cape Hedo was only 1/10-1/20 of those measured in Japanese cities, but a total PAH level comparable with the average levels in Japanese cities was recorded during a long-range transport event in March, 2006.

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The particle samples over Higashiosaka were collected by personal air sampler during asian-dust storms in April of 2005 and 2006. The size and elemental composition of individual perticles were investigated by scanning electron microprobe equipped energy-dispersive X-ray analyzer. From the results of individual particle analysis of Asian dust storm particles, Si-rich particles occupied 76.0% in 2.5-10.0μm diameter particles and 93.0% in <2.5μm diameter particles in April of 2005. In April 2006, Si-rich particles occupied 97.0% in 2.5-10.0μm diameter particles and 99.7% in <2.5μm diameter particles. Anthropogenic sulfur contaminated particles without sea salt were occupied by 2.2% in 2.5-10.0μm diameter particles and 3.6% in <2.5μm diameter particles in April 2005, and those were occupied by 0.4% in 2.5-10.0μm diameter particles and 2.9% in less than 2.5μm diameter particles in April 2006. From these results we confirmed that the degree of adsorption of anthropogenic sulfur oxides on to Asian dust storm particles during transport process from China to Japan was small in 2005 and 2006 over Higashiosaka.

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To clarify the variation of chemical composition of fog water and size distribution of fog droplets, investigation was conducted over the northern North Pacific, where sea fog appears frequently in summer, during the KH-04-3 cruise of R/V Hakuho-maru in 2004. The sea salt composition is governed 65% of total concentration of inorganic ions and the non-sea-salt sulfate occupied 10% in the 90 sea fog water samples. The average size distribution of liquid water content (LWC) of sea fog showed a bimodal pattern with peaks of 7.0 and 27.5μm in diameter, while its distribution on land fog commonly showed a monomodal pattern. LWC, number concentrations of fog droplets and concentrations of sea salt composition were high at the edge of the fog area, and decreased toward the center of the fog area. The peak of LWC was shifted from 17.0μm at the edge to 36.5μm in the center area. Based on the relationship of chemical composition between aerosols and fog droplets, the fog droplets are expected to deposit with growing of its droplet size with coagulation and adsorbing reactive gases as a function of the distance from the edge of the sea fog area. In the northern North Pacific region, frequent sea fog appearance is important as one of scavenge processes of natural and anthropogenic substances from lands as well as marine biogenic substances.

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