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To clarify the characteristics of the water-soluble organic components in atmospheric aerosols, size-separated aerosol samples were simultaneously collected at a roadside site (R) and a suburban background site (S) in Saitama, Japan, during spring and summer 2007 and winter 2008. Chemical compositions, including water-soluble organic carbon (WSOC), organic carbon, inorganic ionic components, and individual water-soluble organic acids (saturated dicarboxylic acids, unsaturated dicarboxylic acids, ketocarboxylic acids, and dicarbonyls), were analyzed in size-separated samples. The seasonal variation of WSOC in Saitama aerosols was larger than the spatial difference between the two sites, with summer WSOC concentrations being 2.5-2.8 times those in the other seasons. Seasonal average concentrations of the detected organic acids in PM 7.0 were 542 ng/m 3 (R) and 670 ng/m 3 (S). Strong correlations were observed between C 2 -C 5 n-dicarboxylic acids and ambient oxidants. The concentration ratios of individual n-dicarboxylic acids (C 2 -C 5 ) to elemental carbon were significantly higher in suburban samples than in roadside samples, indicating that the contribution of secondary formation to these acids was larger in suburban samples. During the warm seasons, the concentrations of sulfate, ammonium, WSOC, and individual acids in fine particles were very high, whereas nitrate, chloride, sodium, and calcium concentrations were higher in coarse particles. Comparisons between the two sites showed that secondary formation contributed more to the total amount of particulate watersoluble organic acids in Saitama aerosols than direct emissions from anthropogenic and natural sources. However, vehicle exhaust was also an important source of dicarboxylic acids in Saitama aerosols, especially in the near-roadside environment.

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The selective elimination of long-lived radioactive actinides from complicated solutions is crucial for pollution management of the environment. Knowledge about the species, structures and interaction mechanism of actinides at solid–water interfaces is helpful to understand and to evaluate physicochemical behavior in the natural environment. In this review, we summarize recent works about the sorption and interaction mechanism of actinides (using U, Np, Pu, Cm and Am as representative actinides) on natural clay minerals and man-made nanomaterials. The species and microstructures of actinides on solid particles were investigated by advanced spectroscopy techniques and computational theoretical calculations. The reduction and solidification of actinides on solid particles is the most effective way to immobilize actinides in the natural environment. The contents of this review may be helpful in evaluating the migration of actinides in near-field nuclear waste repositories and the mobilization properties of radionuclides in the environment.