排序方式： 共有5条查询结果，搜索用时 0 毫秒
1
1.
Norimichi Takenaka Tohru Daimon Akihiro Ueda Keiichi Sato Masaru Kitano Hiroshi Bandow Yasuaki Maeda 《Journal of Atmospheric Chemistry》1998,29(2):135-150
Nitrite oxidation in the tropospheric aqueous phase by freezing was evaluated by freezing a field sample. Nitrite oxidation by dissolved oxygen in the freezing process is much faster than by other oxidation processes, such as reactions with ozone, hydrogen peroxide or dissolved oxygen in an aqueous solution at pHs 3 to –6. At pH 4.5 and 25°C, the lifetime of nitrite in the aqueous phase is ca. 1 hr in oxidation by ozone (6×10-10 mol dm-3), ca. 10 hr in oxidation by H2O2 (2×10-4 mol dm-3), and 7.5 hr (Fischer and Warneck, 1996) in photodissociation at midday in summer. Under the same conditions at a temperature below 0°C, the lifetime of nitrite in the freezing process is estimated as ca. 2 sec when the droplets are frozen within a second. The reaction by freezing is affected by the presence of salts, such as NaCl or KCl, or orgnaic compounds, such as methanol or acetone. The results of freezing a field rain or fog sample showed that nitrite oxidation proceeds below pH 6, and the conversion ratio of nitrate from nitrite increases with decreasing pH. The oxidation of nitrite by freezing was also observed in freezing fog particles generated by an ultrasonic humidifier. The ratios of the concentrations of ions in the winter sample to those in the summer sample (or those in the fog sample) were almost the same values. However, the concentration of nitrite in the winter sample was lower than that estimated by the ratios of other ions. From the present study, it seems that the freezing process plays an important role in the nitrite sink process in the tropospheric aqueous phase. 相似文献
2.
Ammonia (NH3) is the most abundant alkaline gas in the atmosphere and plays a key role in atmospheric chemistry. Reliable and high-time-resolution data for gaseous ammonia are necessary to understand the sources and sinks of ammonia gas in ambient air. In the present study, a sensitive and continuous instrument for measuring gaseous ammonia was developed. Ammonia gas in ambient air was collected in an aqueous solution using a counter-current flow tube (CCFT) sampler. Then, ammonium formed in the aqueous solution was detected by the indophenol method. Based on a CCFT length of 50 cm and air flow rate of 1 L/min, the collection efficiency exceeded 98.5 % at an ammonia mixing ratio of up to 120 ppbv. The detection limit of this method was 0.062 ppbv. Interferences from several gases were investigated, and the results showed that the present method was not affected by NOx, O3, SO2, HONO, methylamine, formaldehyde, hydrogen sulfide or a mixture of these gases. The most important result was that only gaseous ammonia was detected in the present method without any interference from the particulate ammonium in ambient air. Comparisons with data based on the dry denuder method indicated that the present method showed good agreement with the denuder method. 相似文献
3.
M. Tahara K. Uehira H. Shimizu M. Nakada T. Yamada K. Mochizuki M. Shinohara M. Nishino R. Hino H. Yakiwara H. Miyamachi K. Umakoshi M. Goda N. Matsuwo T. Kanazawa 《Physics of the Earth and Planetary Interiors》2008,167(1-2):19-33
The Hyuganada region, a forearc region of Southwest Japan, is characterized by several interesting geological and geophysical features, i.e., significant aseismic crustal uplift of 120 m during the past 120 thousand years at the Miyazaki Plain, negative free-air gravity anomalies with the maximum magnitude of −130 mgal, and relatively less cohesive interplate coupling compared with that for off the Shikoku and Kii Peninsula. In order to examine the causes of these observations, we determined a detailed three-dimensional seismic velocity structure based on the seismic data observed by ocean bottom seismometers (OBS) and land stations. P- and S-wave tomographic velocity structures clearly indicate the subducting slab and also the zones of high Poisson's ratio at 25–35 km depth along the coastline of the northeastern part of the Hyuganada. The region with high Poisson's ratio may correspond to the serpentinized mantle wedge as suggested for other mantle wedges, and appears to be coincident with the zone for observed aseismic slips such as the slow-slip and after-slip events. Also, the detection may be related to a relatively weak interplate coupling in the Hyuganada region. The tomographic structures also indicate low velocity zones with a horizontal scale comparable to the Kyushu-Palau Ridge in and around the subducting slab. If we assume that the low velocity zones correspond to the subducted Kyushu-Palau Ridge, then the predicted gravity anomaly due to the density contrast between the low velocity zones and the surrounding region can explain about 60% of the gravity anomaly in the Hyuganada region. The buoyancy is probably an important factor for the crustal uplift observed in the Miyazaki Plain, the steep bending of the subducting slab and the normal fault-type earthquakes around the Hyuganada region. 相似文献
4.
Tadahide Ui Norimichi Matsuwo Mari Sumita Akihiko Fujinawa 《Journal of Volcanology and Geothermal Research》1999,89(1-4)
Processes generating block and ash flows by gravitational dome collapse (Merapi-type pyroclastic flow) were observed in detail during the 1990–1995 eruption of Unzen volcano, Japan. Two different types were identified by analysis of video records and observations during helicopter flights. Most of the block and ash flows erupted during the 1991–1993 exogenous dome growth stage initially involved crack propagation due to cooling and flowage of the dome lava lobes. The mass around the crack became unstable, locally decreasing in tensile strength. Finally, a slab separated from the lobe front, fragmented progressively from the base to the top within a few seconds, and became a block and ash flow. Rock falls immediately followed, in response to local instability of the lobe front. Clasts in these rock falls fragmented and merged with the preceding flow. In contrast, block and ash flows during the endogenous dome growth stage in 1994 were generated due to local bulge of the dome. Unstable lava blocks collapsed and subsequently fragmented to produce block and ash flows. 相似文献
5.
The heterogeneous interaction of nitrogen dioxide with ammonium chloride was investigated in a molecular diffusion tube experiment
at 295–335 K and interpreted using Monte Carlo trajectory calculations. The surface residence time (τsurf) of NO2 on NH4Cl is equal to 15 μs at 295 K, increases with temperature up to 323 K (τsurf = 45 μs) and probably decreases beyond 323 K. The same experiment also yields uptake coefficients, γ, which are derived from
the absolute number of surviving molecules effusing out of the diffusion tube. The rate of uptake of NO2 on NH4Cl followed a rate law first order in [NO2] and the uptake coefficient γ is equal to 7 × 10−5 at 295 K, increases with temperature up to 323 K (γ = 2.1 × 10−4) and probably decreases beyond 323 K. Nitrous acid, water and nitrogen were detected as products. From these products, it
is concluded that the reaction of NO2 with NH4Cl is a reverse disproportionation reaction where two moles of NO2 result in ammonium nitrite, NH4NO2, as an intermediate, and nitryl chloride, NO2Cl. NH4NO2 decomposes in two pathways, one to nitrous acid, HONO and NH3, the other to nitrogen and water. The branching ratio for the production of HONO + NH3 to that of N2 + H2O is approximately 20 at 298 K and increases with increasing temperature. 相似文献
1