[Show abstract][Hide abstract] ABSTRACT: We estimated the inventories of radiocaesium released by the Tokyo Electric Power Company Fukushima Dai-ichi Nuclear Power Plant (FNPP1) accident to the North Pacific Ocean by using compiled data and model simulations. By comparing the observed inventories with model-simulated results, we obtained 12–15 PBq of 137Cs for the atmospheric deposition released by the FNPP1 accident in the North Pacific Ocean. Before the Fukushima accident, 137Cs activity in the North Pacific Ocean was about 69 PBq. Therefore, the 12–15 PBq of 137Cs newly added by atmospheric deposition together with the 3.5 ± 0.7 PBq added by direct discharge increased the total 137Cs inventory in the North Pacific Ocean by 22–27 %. We also estimated the total amount of 137Cs released to the atmosphere to be 15–20 PBq, and the total amount of 137Cs released to the environment to be 19–24 PBq, respectively. Observed 134Cs to 137Cs activity ratio at the time of accident was close to 1 and extremely uniform, therefore, the total amount of 134Cs deposition in the North Pacific Ocean, that of released to the atmosphere, that of direct discharge to the ocean and that of released to the environment were the same amounts as those of 137Cs.
Journal of Oceanography 11/2015; DOI:10.1007/s10872-015-0332-2 · 1.27 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigated the distribution in seawater of anthropogenic radionuclides from the Fukushima Daiichi Nuclear Power Plant (FNPP1) as preliminary attempt using a rapid aerial radiological survey performed by the U.S. Department of Energy National Nuclear Security Administration on 18 April 2011. We found strong correlations between in-situ activities of 131I, 134Cs, and 137Cs measured in surface seawater samples and gamma-ray peak count rates determined by the aerial survey (correlation coefficients were 0.89 for 131I, 0.96 for134Cs, and 0.92 for137Cs). The offshore area of high radionuclide activity extended south and southeast from the FNPP1. The maximum activities of 131I, 134Cs, and 137Cs were 329, 650, and 599 Bq L−1, respectively. The 131I/137Cs ratio in surface water of the high-activity area ranged from 0.6 to 0.7. Considering the radioactive decay of 131I (half-life 8.02 d), we determined that the radionuclides in this area were directly released from FNPP1 to the ocean. We confirm that aerial radiological surveys can be effective for investigating the surface distribution of anthropogenic radionuclides in seawater. Our model reproduced the distribution pattern of radionuclides derived from the FNPP1, although results simulated by a regional ocean model were underestimated.
Journal of Nuclear Science and Technology 05/2014; 51(9). DOI:10.1080/00223131.2014.914451 · 1.12 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We conducted a source-receptor relationship (SRR) analysis of the
total deposition of nitrate (TDN; dry + wet,
gas + aerosol) in Northeast Asia using an aerosol chemical
transport model. Six regions were included in the study: North China,
Central China, South China, South Korea, Japan, and Ocean. More than 95%
of the TDN across China consisted of contributions from Chinese
emissions. The largest intra-regional contributions and the second
largest contributions were attributed to the Central China region. The
contribution of the three China regions accounted for approximately
50-60% of the TDN in South Korea and Japan and 75% of the TDN in
the Ocean region, respectively. The spatial distributions of the SRR
indicated that the sub-regional high was more than twice the regional
averages of the TDN. We also investigated the effects of sea salt on the
transport and deposition of nitrate. During the long-range transport
from the Asian continent over the ocean, nitric acid gas condenses on
sea-salt particles to form NaNO3. The presence of sea-salt
particles increased the TDN over the downwind regions of the Asian
continent by approximately 10-25% in South Korea and Japan and by
up to 40% in the Ocean region. However, the sea-salt effects on the SRR
of the TDN were small (the absolute differences were smaller than
[Show abstract][Hide abstract] ABSTRACT: We analyzed the source-receptor relationships for particulate polycyclic aromatic hydrocarbon (PAH) concentrations in northeastern Asia using an aerosol chemical transport model. The model successfully simulated the observed concentrations. In Beijing (China) benzo[a]pyren (BaP) concentrations are due to emissions from its own domain. In Noto, Oki and Tsushima (Japan), transboundary transport from northern China (>40°N, 40-60%) and central China (30-40°N, 10-40%) largely influences BaP concentrations from winter to spring, whereas the relative contribution from central China is dominant (90%) in Hedo. In the summer, the contribution from Japanese domestic sources increases (40-80%) at the 4 sites. Contributions from Japan and Russia are additional source of BaP over the northwestern Pacific Ocean in summer. The contribution rates for the concentrations from each domain are different among PAH species depending on their particulate phase oxidation rates. Reaction with O3 on particulate surfaces may be an important component of the PAH oxidation processes.
[Show abstract][Hide abstract] ABSTRACT: Collocated and simultaneous measurements of aerosols near the ground were conducted using a lidar and aerosol sampler at Tsukuba, Japan, to clarify the relationship between lidar-derived optical properties and in-situ microphysical properties. The total linear particle depolarization ratio (δp) ranged from 14% to 18% when nonspherical mineral dust particles were predominant in the supermicrometer range on May 7–8, 2008, whereas it ranged from 6% to 7% when spherical sea-salt particles were predominant in that range on September 3–4, 2008. Sulfates and nitrates were predominant in the submicrometer range for these two periods. Water-dialysis analysis on May 6–7 indicated that 29% of the coarse particles were water insoluble, whereas 70% were water soluble or nearly soluble on September 3–4. The ratio of dry mass concentration to the backscattering coefficient (M/βp) was 34–39 g m−2 sr on May 7–8 and 6.2–6.3 g m−2 sr on September 3–4. Our results provide evidence that lidar-derived βp and δp capture the aerosol mass concentration and relative abundance of the spherical and nonspherical particles although the microphysical properties vary significantly for individual particles.
[Show abstract][Hide abstract] ABSTRACT: (137)Cs is one of the conservative tracers applied to the study of oceanic circulation processes on decadal time scales. To investigate the spatial distribution and the temporal variation of (137)Cs concentrations in surface seawater in the North Pacific Ocean after 1957, a technique for optimum interpolation (OI) was applied to understand the behaviour of (137)Cs that revealed the basin-scale circulation of (137)Cs in surface seawater in the North Pacific Ocean: (137)Cs deposited in the western North Pacific Ocean from global fallout (late 1950s and early 1960s) and from local fallout (transported from the Bikini and Enewetak Atolls during the late 1950s) was further transported eastward with the Kuroshio and North Pacific Currents within several years of deposition and was accumulated in the eastern North Pacific Ocean until 1967. Subsequently, (137)Cs concentrations in the eastern North Pacific Ocean decreased due to southward transport. Less radioactively contaminated seawater was also transported northward, upstream of the North Equatorial Current in the western North Pacific Ocean in the 1970s, indicating seawater re-circulation in the North Pacific Gyre.
[Show abstract][Hide abstract] ABSTRACT: We conducted a regional-scale simulation over Northeast Asia for the
year 2006 using an aerosol chemical transport model, with time-varying
lateral and upper boundary concentrations of gaseous species predicted
by a global stratospheric and tropospheric chemistry-climate model. The
present one-way nested global-through-regional-scale model is named the
Meteorological Research Institute-Passive-tracers Model system for
atmospheric Chemistry (MRI-PM/c). We evaluated the model's performance
with respect to the major anthropogenic and natural inorganic
components, SO42-, NH4+,
NO3-, Na+ and Ca2+ in the
air, rain and snow measured at the Acid Deposition Monitoring Network in
East Asia (EANET) stations. Statistical analysis showed that
approximately 40-50 % and 70-80 % of simulated concentration and wet
deposition of SO42-, NH4+,
NO3-and Ca2+ are within factors of 2
and 5 of the observations, respectively. The prediction of the sea-salt
originated component Na+ was not successful at near-coastal
stations (where the distance from the coast ranged from 150 to 700 m),
because the model grid resolution (Δx=60 km) is too coarse to
resolve it. The simulated Na+ in precipitation was
significantly underestimated by up to a factor of 30.
Geoscientific Model Development 11/2012; 5(6):1363-1375. DOI:10.5194/gmd-5-1363-2012 · 3.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We conducted a regional-scale simulation (with grid spacing = 60 km)
over Northeast Asia for the entire year of 2006 by using an aerosol
chemical transport model, the lateral and upper boundary concentrations
of which we predicted with a global stratospheric and tropospheric
chemistry-climate model, with a horizontal resolution of T42 (grid
spacing ~300 km) and a time resolution of 1 h. The present one-way
nested global-through-regional-scale model is called the Meteorological
Research Institute - Passive-tracers Model system for atmospheric
Chemistry (MRI-PM/c). We evaluated the model performance with respect to
the major inorganic components in rain and snow measured by stations of
the Acid Deposition Monitoring Network in East Asia (EANET). Through
statistical analysis, we show that the model successfully reproduced the
regional-scale processes of emission, transport, transformation, and wet
deposition of major inorganic species derived from anthropogenic and
natural sources, including SO42-,
NH4+, NO3-, Na+
and Ca2+. Interestingly, the only exception was
Na+ in precipitation at near-coastal stations (where the
distance from the coast was from 150 to 700 m), concentrations of which
were significantly underestimated by the model, by up to a factor of 30.
This result suggested that the contribution of short-lived, super-large
sea salt droplets (SLSD; D > 10-100 μm) was substantial in
precipitation samples at stations near the coast of Japan; thus samples
were horizontally representative only within the traveling distances of
SLSD (from 1 to 10 km). Nevertheless, the calculated effect of SLSD on
precipitation pH was very low, a change of about +0.014 on average, even
if the ratio of SLSD to all sea salt in precipitation was assumed to be
Geoscientific Model Development Discussions 06/2012; 5(2):1341-1379. DOI:10.5194/gmdd-5-1341-2012
[Show abstract][Hide abstract] ABSTRACT: A new aerosol chemical transport model, the Regional Air Quality Model 2 (RAQM2), was developed to simulate the Asian air quality. We implemented a simple version of a triple-moment modal aerosol dynamics model (MADMS) and achieved a completely dynamic (nonequilibrium) solution of a gas-to-particle mass transfer over a wide range of aerosol diameters from 1 nm to super-μm. To consider a variety of atmospheric aerosol properties, a category approach was utilized in which the aerosols were distributed into four categories: particles in the Aitken mode (ATK), soot-free particles in the accumulation mode (ACM), soot aggregates (AGR), and particles in the coarse mode (COR). The aerosol size distribution in each category is characterized by a single mode. The condensation, evaporation, and Brownian coagulations for each mode were solved dynamically. A regional-scale simulation (1x = 60 km) was performed for the entire year of 2006 covering the Northeast Asian region. The modeled PM1/bulk ratios of the chemical components were consistent with observations, indicating that the simulated aerosol mixing types were consistent with those in nature. The non–sea-salt SO42− mixed with ATK + ACM was the largest at Hedo in summer, whereas the SO42− was substantially mixed with AGR in the cold seasons. Ninety-eight percent of the modeled NO3− was mixed with sea salt at Hedo, whereas 53.7% of the NO3− was mixed with sea salt at Gosan, which is located upwind toward the Asian continent. The condensation of HNO3 onto sea salt particles during transport over the ocean accounts for the difference in the NO3− mixing type at the two sites. Because the aerosol mixing type alters the optical properties and cloud condensation nuclei activity, its accurate prediction and evaluation are indispensable for aerosol-cloud-radiation interaction studies.
[Show abstract][Hide abstract] ABSTRACT: The emission, concentration levels, and transboundary transport of particulate polycyclic aromatic hydrocarbons (PAHs) in Northeast Asia were investigated using particulate PAH measurements, the newly developed emission inventory (Regional Emission inventory in ASia for Persistent Organic Pollutants version, REAS-POP), and the chemical transport model (Regional Air Quality Model ver2 for POPs version, RAQM2-POP). The simulated concentrations of the nine particulate PAHs agreed well with the measured concentrations, and the results firmly established the efficacy of REAS/RAQM2-POP. It was found that the PAH concentrations in Beijing (China, source region), which were emitted predominantly from domestic coal, domestic biofuel, and other transformations of coal (including coke production), were approximately 2 orders of magnitude greater than those monitored at Noto (Japan, leeward region). In Noto, the PAH concentrations showed seasonal variations; the PAH concentrations were high from winter to spring due to contributions from domestic coal, domestic biofuel, and other transformations of coal, and low in summer. In summer, these contribution were decrease, instead, other sources, such as the on-road mobile source, were relatively increased compared with those in winter. These seasonal variations were due to seasonal variations in emissions from China, as well as transboundary transport across the Asian continent associated with meteorological conditions.
[Show abstract][Hide abstract] ABSTRACT: We developed a new emission inventory for polycyclic aromatic
hydrocarbons (9PAHs; fluorene, pyrene, benzo[a]anthracene, chrysene,
benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene,
benzo[g,h,i]perylene, and indeno[1,2,3-cd]pyrene) in ASia (Regional
Emission inventory in Asia for POP version, REAS-POP) at 0.5x0.5 grid
for the period from 2000 to 2005. By using the REAS-POP, spatial
distributions of PAHs in East Asia were simulated by Regional Air
Quality Model for POP version (RAQM-POP). In REAS-POP, estimated annual
emission of 9PAHs in East Asia was increased from 7.61 Gg yr-1 in 2000
to 10.79 Gg yr-1 in 2005. The China is the dominant PAHs emission
country in East Asia during this period. Area where considerable high
emissions as well as rapid increase rate was found in the northern
central region, North China Plain, Guizhou, Sichuan Basin, and North
East in China. The contribution from various sources for PAHs emission
was different by each country. In the developing country (China,
Democratic People's Republic of Korea, Mongolia, and Russia), dominant
sources of PAHs were domestic coal, domestic biofuel, and other
transformation of coal including cokes production, although contribution
from open biomass burning was relatively large in Russia and Mongol. In
Japan and Taiwan, the road traffic source was identified as the major
source for the 9PAHs emissions. At Beijing, China, simulated PAHs
concentrations were quantitatively agreed with the measured
concentrations during the period from 8 March to 26 May, 2005. In the
case of Wajima, coastal site of the Sea of Japan in Japan, it was
observed clear seasonal variation with high concentrations in winter and
low concentrations in summer in 2005. The measured seasonal variations
were also simulated well. Results with analysis by model simulation
revealed that higher concentrations in winter were due to the high
emission in China in winter and long-range transport from the Asian
continent toward the Japanese islands. In summer, the lower
concentrations result in lower emission in China and prevent of
long-range transport of PAHs under the Pacific high. The geographical
distributions of PAHs emission and concentration suggest that seasonal
variation of PAHs concentrations observed at Wajima were strongly
controlled by emission strength and meteorological conditions.
[Show abstract][Hide abstract] ABSTRACT: Aerosol number concentrations were continuously measured at sites at Tsukuba and Mt. Haruna on the Kanto region of Japan by using optical particle counters (OPCs) from February to June 2007. Three specific dust events captured at the sites were analyzed by using lidar, backward trajectories, and model simulation in detail. The temporal variations in aerosol concentrations in the two Asian-dust events (K1 event: 31 March–3 April; K2 event: 25–28 May) were similar. Dust particles (≥2.0 μm in diameter) were transported in association with a synoptic-scale cold front, and they arrived at the Tsukuba site about 8 h after they were observed at the Mt. Haruna site, in association with the dissipation of a local front formed ahead of the cold front. However, the inflow patterns of dust particles differed between the K1 and K2 events. The K1 event flowed onto the Kanto Plain, detouring around the mountainous region, whereas the K2 event directly flowed across the mountains. The difference in inflow pattern was probably due to the blocking effects of the mountains and the formation of a stable layer near the surface. Preceding the dust plume arrival, an increase in the number concentration of small-aerosol particles (0.3–1.0 μm in diameter), which are considered to be spherical by lidar, was observed, but only at the Tsukuba site. This increase was possibly due to anthropogenic pollution transported over long distances from the continent and from domestic sources in the Kanto region. The third event was a local dust event, because it was observed only at the Tsukuba site (on 13 and 14 March) under dry conditions (10 m s−1).
[Show abstract][Hide abstract] ABSTRACT: As a part of the effort to understand the structure of long-range transported aerosol plumes and local pollution, aerosol observations monitored the mass concentrations and number-size distributions during the period August 2006 to July 2009 near the top of Mt. Haruna (1365 m), an isolated mountain in the Kanto Plain in Japan. The mass concentrations observed at Mt. Haruna and plain sites showed a seasonal variation with a maximum in spring and summer, respectively. The spring peaks in aerosols at Mt. Haruna were probably caused by long-range transport of mineral dust and anthropogenic particles from the Asian continent. The summer peaks at the plain sites was attributed to local pollution from the Tokyo metropolitan area. Three examples of 2007 Asian dust events were investigated to show that aerosols may be dispersed in a complicated three-dimensional structure and that delayed arrivals of the dust plumes at plain sites compared to Mt. Haruna were not a rare case. Because of the boundary layer being stable at night, the dust layer was advected eastward without the vertical mixing before sunrise. This study suggests that after thermal convection activated by sunlight during daytime Asian dust transported in the free troposphere may be brought down into the atmospheric boundary layer, increasing the dust concentration there.
[Show abstract][Hide abstract] ABSTRACT: Concentrations of 222Rn were observed at the summit of Mt. Fuji (35.4°N, 138.7°E; 3776 m above sea level) in Japan from October 2002 to September 2003. These observations were analyzed using a global three-dimensional model. Daily 222Rn concentrations varied from 0.2 to 2.5 Bq m−3. The variation exhibited a slight seasonal cycle with high values in winter and summer. Day-to-day variation of 222Rn concentrations in winter had a large amplitude, depending on differences in transport processes from the Asian continent. In winter, higher concentrations of 222Rn were observed in an air mass with ascending motion advected from the middle latitudes of the eastern Asian continent where the 222Rn concentration of the air mass was high. In contrast, a lower concentration was observed in the air mass in winter, with a descending motion advected from Siberia where the 222Rn amount was low. The high amplitude of temporal variation of 222Rn in summer was due to the alternation of air masses originated from the continent or the ocean. The relatively low amplitude of day-to-day variation during spring and autumn was a reflection of the vertically uniform distribution of 222Rn in the air column over the Asian continent, where uniformity was produced by vertical mixing due to turbulence and thermal convection. The seasonal variation was linked to the East Asian monsoon circulation, with the westerly jet shifted northward or southward depending on the season. The main export of 222Rn was around 25 to 55°N during the winter and into the spring, shifting northward to around 30–70°N during the summer.
[Show abstract][Hide abstract] ABSTRACT: Both wet and dry deposition fluxes of Aeolian dust were analyzed for over one year (from March 2007 to May 2008) including two dust seasons in Tsukuba, Japan. The annual wet and dry deposition fluxes of dust were 5.5 g m-2 and 3.8 g m-2, respectively. The largest wet deposition flux associated with the one heavy Asian dust event was 0.95 g m-2, which accounted for 10% to the annual total deposition. A typical feature of the deposition fluxes marked seasonal variation with higher deposition in spring. Furthermore, the wet deposition fluxes in the spring (March-May) 2007 were larger than those in 2008. The temporal variations of wet depositions were agreed well with the model simulation. Analysis of model simulation showed that the seasonal and year to year variations of the wet deposition fluxes in Tsukuba could be closely connected with the variation of dust emission over the Asian continent associated with stronger wind. For dry deposition fluxes of dust, local dust near the observation region also contributed to the deposition fluxes in addition to the Asian dust.
Scientific online letters on the atmosphere: SOLA 10/2009; 5:153-156. DOI:10.2151/sola.2009-039 · 0.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Monthly plutonium and thorium depositions at Tsukuba (28m asl) and Mt. Haruna (1370m asl) were measured during 2006 and 2007 (Jan 2006-Dec 2007 at Tsukuba, Nov 2006-Dec 2007 at Mt. Haruna). The monthly (239,240)Pu depositions ranged from 0.044 to 2.67mBq m(-2) at Tsukuba and from 0.05 to 0.9mBq m(-2) at Mt. Haruna during the measurement periods. Monthly (239,240)Pu deposition did not differ markedly between the two sites except in April 2007. Seasonal pattern of monthly (239,240)Pu depositions at both sites showed high in spring and low in summer, and typical of seasonal variations in northeastern Asia. Thorium deposition at Tsukuba was higher than that at Mt. Haruna except in May and June 2007. (230)Th/(232)Th activity ratios were used to partition deposition samples into locally and remotely derived fractions. The results revealed that a major proportion of total (239,240)Pu and Th deposits are derived from remote sources, especially in spring.
[Show abstract][Hide abstract] ABSTRACT: Dry and wet depositions were sampled daily in Tsukuba, Japan, in spring 2007. Temporal variations in the dry and wet deposition fluxes of dust and water-soluble chemical species were controlled largely by air mass origin, the water vapor mixing ratio, and Asian dust events. The contribution of local sources to dry deposition of dust was large when the wind speed was high. Dry deposition fluxes of water-soluble chemical species were larger in humid air masses than in dry air masses. Wet deposition fluxes of dust and water-soluble chemical species indicated that air masses that passed over dust source regions and industrial regions became mixed with the maritime air masses over the coastal site of the Asian continent and western part of the Japanese islands. The total deposition of dust was 4220 mg m−2 month−1, and that of water-soluble chemical species ranged from 10 to 636 mg m−2 month−1. Wet deposition fluxes of the total deposition flux of dust accounted for 72% and those of water-soluble chemical species was for 72–96%. In particular, the largest wet deposition occurred during a single Asian dust event on 3 April. This event accounted for 23% (950 mg m−2 month−1) of the monthly dust deposition flux and for 2–28% (0.43–51 mg m−2 month−1) of the monthly deposition flux of water-soluble chemical species. This result implies that the wet deposition flux associated with even one sporadic Asian dust event can have extensive impacts on both terrestrial and oceanic ecosystems in East Asia.
[Show abstract][Hide abstract] ABSTRACT: A paper written in Japanese! Aiming at deconvolution of the dust event into local and remote elements, physical and chemical aerosol observations were carried out at the Meteorological Research Institute in Tsukuba, Japan in spring of 2006. During the observation there were two remarkable dust events with the maximum aerosol mass concentration attained to a few hundred μg/m3 (hourly value), which were selected for close scrutiny. Based on the meteorological observations over the Japanese islands, backward-trajectory analysis and the CTM calculations, it was concluded that they had different origins. One was Asian dust transported from the continent (Kosa) and the other was blowing dust from neighborhood. Therefore, physical and chemical characteristics of these were compared. For the case of the blowing dust event during its evolution (the dust mass was increasing), number concentrations of larger particles increased remarkably, while those increased concurrently by all particle size bins of the optical particle counter for the Kosa event. In the analysis of the water soluble ions, the Kosa dust showed about twice higher concentrations as well as the ratio of nss-Ca2+ and nss-SO42- to the total dust mass compared to those of the local blowing dust. NO3- also exhibited significantly high concentration for the Kosa dust. Further accumulation of such differences in physical and chemical nature of the dust may bring a potential criterion to distinguish the Kosa and the local blowing dust events over Japan.