Yukimasa Ikebe

Seasonal characteristics of organic and inorganic species and their size distributions in atmospheric aerosols over the northwest pacific ocean

Abstract In order to investigate the chemical properties of marine aerosols and the long-distance transport of continental aerosols to remote oceanic regions, simultaneous measurements of chemical compounds in atmospheric aerosols, cloud condensation nuclei (CCN) and associated species were conducted from December 1994 to January 1997 at Hahajima, the Ogasawara Islands, in the northwest Pacific Ocean, being located on the lee of the large east Asian polluted region. Clear change of air quality, caused by air mass alternation, are found. Concentrations of CCN and aerosol chemical species, such as non-sea-salt sulfate, nitrate, and oxalate, are low under the marine background conditions, whereas largely increased under the continentally affected conditions. It is ascertained that long-distance transport of these species to the remote ocean continues during half-year periods. Seasonal characteristics and size distributions of particulate organic acids, previously not well understood in earlier studies, are clarified. It is found that formate and acetate could have marine biogenic sources, mostly existing as coarse particles, whereas the oxalate was influenced by continental anthropogenic activity, displaying a relative predominance in the accumulation mode.

Continuous measurements of outdoor radon concentrations at various locations in East Asia

Abstract Four electrostatic radon monitors were constructed to continuously measure outdoor 222 Rn concentrations at various locations. Outdoor 222 Rn concentrations were measured at six locations in Japan and China. The annual mean 222 Rn concentrations at Nagoya, Kasugai, Toki, and Kanazawa in Japan were 5.1, 6.0, 6.1, and 5.8 Bq m −3 , respectively. The 222 Rn concentrations at Nagoya, Kasugai, and Toki showed a diurnal variation clearly in autumn and a seasonal pattern of a spring-summer minimum and an autumn-winter maximum. The 222 Rn concentrations at Kanazawa showed a diurnal variation clearly in summer. At Beijing and Fuzhou in China, the annual mean concentration levels were 7.0 and 11.4 Bq m −3 and the pattern of the diurnal variations was different from that at Nagoya. The seasonal variations of a summer minimum and a winter maximum were almost similar at Beijing and Fuzhou

An electrostatic integrating 222Rn monitor with cellulose nitrate film for environmental monitoring.

This paper describes a new type of electrostatic integrating 222Rn monitor designed for the environmental 222Rn monitoring. The window area of the monitor was selected to make the exchange rate optimal. The collecting electrode was positioned on the basis of calculating the internal electric field. A drying agent, P2O5, was placed in the bottom of the monitor, since the collection efficiency of 218Po+ atoms depends on the humidity of the air. The monitors have been calibrated against known 222Rn exposures. The detection limit is 1.2 Bq m-3 for an exposure time of 2 mo. In a small survey, annual mean 222Rn concentrations between 3.7 and 9.5 Bq m-3 in outdoor air and between 6.4 and 11.9 Bq m-3 in indoor air were measured.

Estimation of areal flux of atmospheric methane in an urban area of Nagoya, Japan, inferred from atmospheric radon-222 data

Abstract To clarify the emission of methane (CH4) from area sources, we have adopted atmospheric radon-222 (222Rn) as a natural tracer. The diurnal variation in CH4 concentration is predominantly affected by local meteorological conditions as is the case of 222Rn. Positive correlations are recognized between atmospheric CH4 and 222Rn concentrations. From these correlations, the CH4 flux from urban area in Nagoya, Japan, was estimated to be almost constant at 0.02 gCH4m−2d−1 over a year.

Carbon isotopic analysis of atmospheric methane in urban and suburban areas : Fossil and non-fossil methane from local sources

The carbon isotopic composition (12C, 13C and 14C) of atmospheric CH4 was studied to estimate CH4 sources in local areas. In urban areas of Nagoya, Japan (35°10′N, 136°55′E), where there is much anthropogenic influence, evidence of methane release into the atmosphere has been reported. Variations in the carbon isotopic composition were analyzed with diurnal fluctuation of atmospheric CH4 concentration, since the diurnal increase in the CH4 concentration is attributed mainly to release from local sources. In November and December 1993, the contribution of fossil CH4 to local CH4 released from the urban area was calculated to be 102±8%, and its δ13C was −40.8±3.0‰. Leakage of supplied natural gas and exhaust gas from automobiles would be important CH4 sources in the urban area in late autumn to winter. In suburban areas in Japan there are many rice paddy fields, and these are one kind of major anthropogenic source of atmospheric CH4. In a suburban area of Nagoya fossil, CH4 contributed to less than 10% of local release in July and August 1994. The calculated value of δ13C for non-fossil CH4 was approximately −65‰, which is within the range of reported values of δ13C for CH4 derived from bacterial CH4 sources such as irrigated rice paddies.

Measurement of small ions and condensation nuclei over the sea near the land

SummaryTo study the ionization equilibrium, simultancous measurements of the concentration of small ions (n), concentration of condensation nuclei (Z), and the diffusion coefficient of condensation nuclei (D) have been carried out over the sea. If we take the variation ofD into consideration, the correlation among them was found to be well expressed by the simple formula;q=βn Z. The dependence of the effective attachment coefficient of small ions (β) upon the size of nuclei (2r) were also studied, and β was found to correlate well withD orr. Slight differences of the dependence of β uponD orr over the sea from that over the land seem to be well explained by the difference of charged states of nuclei over the sea and land.ZusammenfassungZur Untersuchung des Ionisationsgleichgewichts wurden gleichzeitige Messungen der Konzentration schneller Ionen (n), der Konzentration der Kondensationskerne (Z) und des Diffusions-Koeffizienten der Kondensationskerne (D) über dem Meere ausgefürt. Unter Berücksichtigung des Diffusions-Koeffizienten (D) konnte der Zusammenhang zwischen den beiden anderen Grössen recht gut durch eine einfache Formel ausgedrückt werden:q=βn Z. Die Abhängigkeit des wirksamen Anlagerungskoeffizienten für schnelle Ionen (β) von der Grösse der Kondensationskerne (2r) wurde ebenfalls untersucht, und es wurde gefunden, dass β recht gut mitD oderr korreliert. Kleinere Unterschiede in der Abhängigkeit von β vonD oderr, welche bei einem Vergleich der Messungen über See und über Land festgestellt wurden, liessen sich gut durch den Unterschied der geladenen Zustände der Kondensationskerne über See und Land erklären.

An alpha-particle imaging system for detecting plutonium contamination

Abstract A new type of alpha-particle imaging system was constructed to reduce the time required for detecting plutonium contamination. The imaging system consists of a ZnS(Ag) screen, two tapered fibers, an image intensifier, and Polaroid film. Spots due to single alpha-particles can easily be obtained on the Polaroid film. The observed spatial resolution is more than 3 lp/mm. This system requires about one-seventh of the exposure time required by ZnS(Ag) autoradiography in order to distinguish between plutonium contamination and radon and thoron daughter products.

Some problems on the measurement of 222Rn concentrations by passive cup method.

A passive cup monitor has been constructed by using a 50 mm radius stainless steel hemisphere. The conductive housing has reduced the scatter in track densities. In dwellings with high 220Rn concentrations, it is particularly necessary to measure 222Rn concentration with a monitor having a radon exchange rate less than 0.1 h-1.

Dependence of the effective attachment coefficient of small ions upon the size of condensation nuclei

SummaryTo clarify the ionization equilibrium near the ground, simultaneous measurements of the rate of ion pair production (q), the concentrations of small ions (n) and condensation nuclei (Z), and the diffusion coefficient of condensation nuclei (D) were carried out at several stations in the central area of Japan. The total rate of ion pair production (q) was estimated fromq=q(Rn)+q(Tn)+q(β)+q(γ+CR). The value ofq was estimated as 10J to 20J. The mean life (θ) and the effective attachment coefficient (β) of small ions were also estimated at each station. Correlations amongn, Z, q, andD were also studied. If we take the variation ofD into consideration, the correlation was expressed by the simple formula;q=βn Z. The dependence of β upon size of nuclei (2r) were also measured, and β was found to correlate well withD orr.

A low-energy beta-particle imaging system for measuring tritium distributions

Abstract A low-energy beta-particle imaging system was constructed for rapid measurement of the distributions of low-energy beta-emitting nuclides, especially tritium. The imaging system consists of a scintillator screen, two tapered fibers, an image intensifier, and a Polaroid film for image recording. The distortion of the observed image is less than 2.5% and the spatial resolution is more than 5 line pairs (lp)/mm. ZnS(Ag) screens with thicknesses of 5–7 mg/cm 2 have the highest scintillation light yield for low-energy beta-particles. The detectable flux densities for 14 C and 3 H were 7.3 and 80 s −1 cm −2 , respectively.