Yuji Zaizen

Emission of spherical cesium-bearing particles from an early stage of the Fukushima nuclear accident

The Fukushima nuclear accident released radioactive materials into the environment over the entire Northern Hemisphere in March 2011, and the Japanese government is spending large amounts of money to clean up the contaminated residential areas and agricultural fields. However, we still do not know the exact physical and chemical properties of the radioactive materials. This study directly observed spherical Cs-bearing particles emitted during a relatively early stage (March 14–15) of the accident. In contrast to the Cs-bearing radioactive materials that are currently assumed, these particles are larger, contain Fe, Zn, and Cs, and are water insoluble. Our simulation indicates that the spherical Cs-bearing particles mainly fell onto the ground by dry deposition. The finding of the spherical Cs particles will be a key to understand the processes of the accident and to accurately evaluate the health impacts and the residence time in the environment.

The mixture state of individual aerosol particles in the 1997 Indonesian haze episode

Abstract The mixture state of individual aerosol particles collected at altitudes of 1– 5 km on 23 and 25 October 1997, from an aircraft flying over southern Kalimantan during the 1997 Indonesian forest fires, has been examined using the dialyses of water-soluble material with water, and organic material with benzene in conjunction with electron microscopy. Individual aerosol particles in the radius range of 0.1– 2 μm were mainly present as an internal mixture of water-soluble organic material and inorganic salt (mainly ammonium sulfate). Although material comprised of chain aggregations of electron-opaque spherules (elemental carbon) was also found, the proportion of these was small.

Backscattering linear depolarization ratio measurements of mineral, sea-salt, and ammonium sulfate particles simulated in a laboratory chamber

The backscattering linear depolarization ratios of major types of tropospheric aerosol particles (Asian and Saharan mineral dust, sea salt, and ammonium sulfate) were measured using a laboratory chamber for interpreting the polarization lidar measurement of tropospheric aerosols. The values obtained from Asian and Saharan mineral particles were 0.39 +/- 0.04 to 0.05 (mean +/- standard deviation) for a high number of concentrations in the supermicrometer range and 0.17 +/- 0.03 to 0.14 +/- 0.03 in the submicrometer range. The values were 0.08 +/- 0.01 for sea-salt crystals, 0.04 +/- 0.003 for ammonium sulfate crystals, and 0.01 +/- < or = 0.001 for both liquid droplets in the submicrometer range. These values can serve as a reference for estimating aerosol type using lidar measurement.

Tropospheric ozone measurement at the top of Mt. Fuji

Since August of 1992, tropospheric ozone has been measured at the top of Mt. Fuji to investigate the background ozone feature of middle troposphere over Japan. During one year, the maximum concentration of monthly mean ozone at Mt. Fuji was 59.3 ppbv in May and minimum was 30.9 ppbv in August. The secondary minimum was recorded in January. The seasonal behavior showed a bi-modal trend. The diurnal amplitude of ozone in summer showed slight effect from the mountain and valley winds, but the amplitude around 2 ppbv is a lot smaller compared to other mountain data. The amplitude of other seasons did not show any significant variations. The effect of the mountain and valley winds were small at the top of Mt. Fuji because of the steep and windy summit. Day-to-day summertime variations varied wildly and often recorded low concentrations of ozone less than 20 ppbv. This low concentration of ozone sometimes continued for 3–5 days. This summer ozone minimum of the lower free troposphere was due to horizontal advection of the ozone poor air. In wintertime, the deviation of ozone concentration was very small. High peaks which lasted only a few hours were observed in spring. Analyzing the cross section chart on the 14th May 1993, the high peak of ozone on this day must have come from the stratosphere along the isentropic surface.

Case studies of tropospheric ozone events observed at the summit of Mount Fuji

Tropospheric ozone events observed at the summit of Mount Fuji (3776 rn above sea level) were analyzed as case studies. The ozone, intruding from the lower stratosphere by the cutoff low or the tropopause fold over the Asian continent, is transported to the middle troposphere over Japan even in summer. The subtropical jet, which is intensified over Japan, also contributes to the summer intrusion from the stratosphere. A long stratospheric streamer, as described previously by Appenzeller et al. ( 1996), brings about a persistent ozone enhancement at the summit of Mount Fuji. The large variation of summer ozone over Japan is attributable to the alternate overspreading of these ozone-rich stratospheic air masses and the ozone-depleted subtropical maritime air mass. In contrast, winter ozone variation is relatively small at the summit of Mount Fuji. The steep potential temperature gradient between 500 hPa and 300 hPa in the winter cutoff low, which restrains vertical mixing in the upper troposphere, possibly causes less influence of the stratospheric air mass on the middle troposphere in winter, since mixing processes around a cutoff low play an important role in air mass exchange between the stratosphere and the troposphere.

Mixing state of regionally transported soot particles and the coating effect on their size and shape at a mountain site in Japan

Soot particles influence the global climate through interactions with sunlight. A coating on soot particles increases their light absorption by increasing their absorption cross section and cloud condensation nuclei activity when mixed with other hygroscopic aerosol components. Therefore, it is important to understand how soot internally mixes with other materials to accurately simulate its effects in climate models. In this study, we used a transmission electron microscope (TEM) with an auto particle analysis system, which enables more particles to be analyzed than a conventional TEM. Using the TEM, soot particle size and shape (shape factor) were determined with and without coating from samples collected at a remote mountain site in Japan. The results indicate that ~10% of aerosol particles between 60 and 350 nm in aerodynamic diameters contain or consist of soot particles and ~75% of soot particles were internally mixed with nonvolatile ammonium sulfate or other materials. In contrast to an assumption that coatings change soot shape, both internally and externally mixed soot particles had similar shape and size distributions. Larger aerosol particles had higher soot mixing ratios, i.e., more than 40% of aerosol particles with diameters >1 µm had soot inclusions, whereas <20% of aerosol particles with diameters <1 µm included soot. Our results suggest that climate models may use the same size distributions and shapes for both internally and externally mixed soot; however, changing the soot mixing ratios in the different aerosol size bins is necessary.

Aircraft Observation of CO2, CO, O3 and H2 over the North Pacific during the PACE‐7 Campaign

Aircraft observation under the Pacific Atmospheric Chemistry Experiment (PACE) program was performed from February 13 to 21, 2000 to examine in detail the distributions of CO2 in the free troposphere between 5 and 11 km. Continuous measurements of CO2mixing ratios were made using an on-board measuring system over the northern North Pacific between Nagoya, Japan and Anchorage, Alaska, and the western North Pacific between Nagoya and Saipan. Other trace gases, such as CO and O3, were also observed using continuous measuring systems at the same time. CO2 over the northern Pacific (35¼N and higher) showed highly variable mixing ratios, ranging from 374 ppm in the upper troposphere to 366 ppm in the lowermost stratosphere. This highly variable distribution of CO2 was quite similar to that of CO, but the relationship between CO2 and O3 showed a strong negative correlation. These results indicated that the exchange process between the stratosphere and the troposphere significantly influences the large CO2variation. On the other hand, the CO2 over the western North Pacific to the south of Japan showed no significant variation in the upper troposphere at 11 km but a relatively larger variability at 5 km. The CO2 enhancement at lower altitudes coincided with the CO elevation due to the intrusion of a polluted air mass. Trajectory analysis indicated that the Asian continental outflow perturbed the CO2 distributions over the western Pacific. Very low mixing ratios of O3 of less than 20 ppb were distributed in the latitude band of 15–30¼N at 11 km, reflecting the effects of transport from the equatorial region.

Number concentration and size distribution of aerosol particles in the middle troposphere over the Western Pacific Ocean

Number concentration and size distribution of aerosol particles were measured on board aircraft during the PACE (Pacific Atmospheric Chemistry Experiment) campaign from Australia to Japan in January 1994. The spatial distribution of condensation nuclei (CN) (r ≥ 4 nm) at 5-6 km altitude showed large variabilities in concentrations from 10 2 to 10 3 mg -1 ; that is, the concentrations were low (70-500 mg -1 ) in the intertropical convergence zone, high (400-1500 mg -1 ) in the subtropical high-pressure area, and low again in the higher latitudes. An apparent opposite tendency was present between CN and large particle (r≥0.15 μm) concentrations. The size distributions in the subtropical region exhibited high number concentrations of very fine particles (r < 0.02 μm). Together with the horizontal observation, vertical observations of aerosols were carried out over some areas. In the subtropical area (Saipan), CN concentration increased with altitude in contrast to the large particle concentration. Also most of the particles collected at 6 km altitude over Saipan contained sulfuric acid. These results are consistent with the results of Clarke (1993, J. geophys. Res. 98,20,633-20,647)that new particle formation is favored in the upper troposphere.

Aircraft measurement of dicarboxylic acids in the free tropospheric aerosols over the western to central North Pacific

Aircraft observation of aerosols was conducted in February 2000, for spatial and vertical distributionsof dicarboxylic acids in the free troposphere over the western to central North Pacific. Oxalic, malonic, adipic and azelaic acids were detected in the aerosol samples as the major species. Concentrations ofthese diacids decreased exponentially with an increase in altitude. They were higher in the westernNorth Pacific (130°E) and decrease eastward. Local flights conducted over Naha (Okinawa), Iwojimaand Saipan showed that diacid concentrations decreased from the lower to upper troposphere.In the atmosphere over Saipan, where the air is not strongly affected from polluted East Asia, diacidconcentrations were almost below the detection limit. Vertical profiles of diacids over Naha and Iwojimawould be typical over the western North Pacific during winter, suggesting that diacids weresignificantly injected to the free troposphere from East Asia. Backward air mass trajectories alsosuggested that the diacids in the free troposphere over the North Pacific are strongly affected bythe outflow from East Asia. Diacids, which were produced by both primary emission and secondaryphotochemical processes in polluted air of East Asia, could alter the physico-chemical properties ofaerosols in the free troposphere over the western North Pacific.