Summarized are the actual field investigations, which include the advection and deposition of drying components and acidification of the environment, and the air purification technology using activated carbon fibers (ACFs). The air purification technology using ACFs regards natural wind or air flow as the driving force without electric energy. Some 1,000 fundamental experiments have already been implemented for evaluating the ACFs. However, it was difficult to prove in the field any technology established in laboratory experiments. The reason is that the temperature / humidity or wind direction/speed of the outside air is always changing and a wide variety of gases and aerosols are mixed together. In order to put the ACFs into practical use, it is required to reduce the production/running costs, simplify the handling operation and produce a high performance as opposed to previous issues. It is also necessary to take into consideration the ACF regeneration technology after using it and decrease the life cycle CO₂ emissions. Most of the above mentioned matters were generally understood. Meanwhile, some related technologies are being investigated. The air purification technology using the ACF will be described in the majority of general remarks and its development process explained, along with the current excellent results and future prospects.

View full abstract

Scavenging ratios of aerosolsfor rain and snow were evaluated in order to examine the scavenging process of aerosols by precipitation in a coastal area of the Sea of Japan during winter seasons. Concentrations of chemical constituents in precipitation and ambient aerosol were measured at a site in Niigata during the winter seasons of 2008 - 2011. The geometric mean of the scavenging ratio of sea-salt components for snow was approximately two or three times greater than that for rain, whereas the geometric mean of the scavenging ratio of non-sea-salt components for snow was almost equal to that for rain. The scavenging ratio of Na⁺ for snow remained almost constant with surface air temperature, while that for rain decreased with the temperature, falling to approximately one order lower than that for snow. The extent of decrease in the scavenging ratio of nss-SO₄^2- for rain with increasing surface air temperature was smaller than that of Na⁺ for rain. The difference in the scavenging ratio of sea-salt components between snow and rain would be attributed to the greater contribution of below-cloud scavenging to precipitation scavenging of sea-salt aerosol compared to that of non-sea-salt aerosols, and the higher efficiency of below-cloud scavenging of aerosols for snow than that for rain.

View full abstract

The continuous monitoring of a size-segregated ambient aerosol was performed in order to reveal the detailed process of transboundary transport of Kosa and anthropogenic substances at Kyoto City, Japan, on the Kosa day, December 26, 2009. Every 1-hour aerosol sample of both the fine (PM_2.5) and coarse (PM_10-2.5) fractions were simultaneously collected on a filter roll composed of PTFE using an automated dichotomous aerosol monitor. The ionic components and inorganic elements in the aerosols were quantified. Meteorological observations indicated that a cold front passed through before 15:00 on December 26 (JST). At that time, air polluted with high concentrations of anthropogenic SO₂, fine ammonium sulfate, Pb and coarse nitrate appeared during a 4-hr period to 15:00 on December 26. The inorganic elemental ratio (Pb/Zn) and backward trajectories analysis showed that the polluted air mass was transported through Eastern China producing a large amount of SO₂. The polluted air mass was then rapidly replaced by an air mass mainly composed of Kosa particles, and the replacement was completed before 19:00 on December 26. The plume mainly composed of Kosa did not cause any chlorine depletion in the coarse sea-salt particles. Our observations showed the detailed transport process and chemical properties of anthropogenic substances and Kosa derived from the Asian continent.

View full abstract

To evaluate the influence of the long-range transported atmospheric pollutants on the vegetation, we measured the dry deposition of anions and leaching of cations from the needles of two pine species, Pinus armandii var. amamiana (Paa) on Yakushima Island and Pinus dendiflora Sieb. et Zucc. (Pde) on the Kirishima mountains, southwestern Japan. In both species, we found the dry deposition on 1-year-old needles more than on current-year ones. We detected F^- in the dry deposition on the needles of Paa, suggesting that F^- originated from China based on the results of a back trajectory analysis, because atmospheric F^- was detected at higher concentration in China. We found Ca²⁺ and Mg²⁺ besides K⁺ in the leachate from both species, suggesting that these cations were leached from the cytoplasm after degradation of the needles’ surfaces. The dry deposition of anions and leaching of cations were strongly correlated (r=0.71-0.96, p<0.01) in Paa. However, we found no significant correlations between the dry deposition and leaching in Pde. Our results suggest that dry deposition was the main cause of the increased leaching from the needles of Paa, whereas other factors were more important for Pde. In addition to the dry deposition, photochemical oxidants may negatively affect these pine species in these natural habitats.

View full abstract

The photochemical oxidant (Ox) concentrations observed at the monitoring site located in Aso somma (930 m) in the area of central Kyushu from April 2011 to May 2012 were used for evaluating the contributions of transportation from the continent, intrusion of the stratospheric ozone, and local photochemical Ox production. As the averaged diurnal change in the Ox concentrations was low, the Ox observed during the nighttime was regarded as the background Ox. In the spring, since the daytime Ox concentration data from multiple sites (including Aso somma and ground-based monitoring sites) showed almost the same level, as the averaged behavior in this season, the authors considered that the Ox level of the ground-based monitoring sites depended on vertical mixing of the background Ox in the upper layer. Based on the averaged diurnal change in the Ox concentration at the site in Aso somma, contributions of the averaged local photochemical Ox production to the daytime maximum value of Ox were estimated to be less than 10 % except in the summer season. On the other hand, based on evaluating the contributions for each day when high Ox concentration were observed, some cases showed the possibility that the contributions of the local photochemical Ox production were over 20 ppb. As the result of a multiple correlation analysis for the daily averaged Ox concentrations in the spring using the specific humidity and sulfate as variables, the authors considered that the background Ox in this season consisted of adding transportation from the continent to the base Ox concentration from intrusion of the stratospheric ozone.

View full abstract