Search

On the basis of the recently estimated emission inventory for East Asia with a resolution of 1×1°, the transport and chemical transformation of sulfur compounds over East Asia during the period of 22 February through 4 May 2001 was investigated by using the Models-3 Community Multi-scale Air Quality (CMAQ) modeling system with meteorological fields calculated by the regional atmospheric modeling system (RAMS). For evaluating the model performance simulated concentrations of sulfur dioxide (SO2) and aerosol sulfate (SO42−) were compared with the observations on the ground level at four remote sites in Japan and on board aircraft and vessel during the transport and chemical evolution over the Pacific and Asian Pacific regional aerosol characterization experiment field campaigns, and it was found that the model reproduces many of the important features in the observations, including horizontal and vertical gradients. The SO2 and SO42− concentrations show pronounced variations in time and space, with SO2 and SO42− behaving differently due to the interplay of chemical conversion, removal and transport processes. Analysis of model results shows that emission was the dominant term in regulating the SO2 spatial distribution, while conversion of SO2 to SO42− in the gas phase and the aqueous phase and wet removal were the primary factors that controlled SO42− amounts. The gas phase and the aqueous phase have the same importance in oxidizing SO2, and about 42% sulfur compounds (∼25% in SO2) emitted in the model domain was transported out, while about 57% (∼35% by wet removal processes) was deposited in the domain during the study period.

領域気象モデルRAMSを用いて九州地域を対象に二重ネスティング法による通年計算を行った. 計算結果は風速, 気温, 降水量を九州地域の気象官署の観測データと比較し再現性を確認し, 計算結果による風速頻度分布はレイリー分布と非常に良い一致を示した. 典型的な風力発電機を設置仮定して発電量などを見積もった. 風力発電能は季節風の影響が強い冬季で高い値を示し, 特に離島, 日本海や東シナ海に沿った海岸地域そして阿蘇などの山岳地域は年間平均風速が強く, 発電取得量が高いことが明らかになった. レイリー分布を用いた発電取得量は一時間間隔の計算結果を時間積算することによって算定した発電取得量より過小評価を示した.

We deployed multi-wavelength Mie-Raman lidars (MMRL) at three sites of the AD-Net and have conducted continuous measurements using them since 2013. To analyze the MMRL data and better understand the externally mixing state of main aerosol components (e.g., dust, sea-salt, and black carbon) in the atmosphere, we developed an integrated package of aerosol component retrieval algorithms, which have already been developed or are being developed, to estimate vertical profiles of the aerosol components. This package applies to the other ground-based lidar network data (e.g., EARLINET) and satellite-borne lidar data (e.g., CALIOP/CALIPSO and ATLID/EarthCARE) as well as the other lidar data of the AD-Net.

An intercomparison study involving eight long-range transport models for sulfur deposition in East Asia has been initiated. The participating models included Eulerian and Lagrangian frameworks, with a wide variety of vertical resolutions and numerical approaches. Results from this study, in which models used common data sets for emissions, meteorology, and dry, wet and chemical conversion rates, are reported and discussed. Model results for sulfur dioxide and sulfate concentrations, wet deposition amounts, for the period January and May 1993, are compared with observed quantities at 18 surface sites in East Asia. At many sites the ensemble of models is found to have high skill in predicting observed quantities. At other sites all models show poor predictive capabilities. Source–receptor relationships estimated by the models are also compared. The models show a high degree of consistency in identifying the main source–receptor relationships, as well as in the relative contributions of wet/dry pathways for removal. But at some locations estimated deposition amounts can vary by a factor or 5. The influence of model structure and parameters on model performance is discussed. The main factors determining the deposition fields are the emissions and underlying meteorological fields. Model structure in terms of vertical resolution is found to be more important than the parameterizations used for chemical conversion and removal, as these processes are highly coupled and often work in compensating directions.

Open biomass burning (OBB) has been reported to emit substantial amounts of non-methane hydrocarbons (NMHCs), and the mixing of OBB with urban plumes could exacerbate regional ozone (O3) pollution. In the present study, an observational field campaign was performed in a rural area at the edge of Yangtze River Delta region (YRDR) during harvest season when intensive open burning of wheat residues was observed. The O3 production rate at the site was calculated using a photochemical box model (Regional Atmospheric Chemical Mechanism, Version 2) constrained by real-time ambient measurements (e.g., O3, volatile organic compounds (VOCs), the sum of NO2 + NO (NOx), J values). During the period impacted by OBB, the O3 concentration frequently exceeded 100 ppbv. Analysis showed that the net O3 production was pronounced, in particular when the site was characterized by a prevailing southerly wind that also brought substantial amounts of NOx emitted from urban areas. At these times, the maximum rate of O3 production was 20 ppbv h−1 with potential production rate of 102 ppbv on a daily basis. The O3 production at the site was typically VOC-sensitive in the morning because NOx dominated the plumes. However, in the afternoon, conditions became NOx-sensitive due to the rapid photochemical consumption of NOx in the production of O3. A positive matrix factorization analysis indicated that solvent usage and OBB were the primary contributors to the mass fraction of ambient NMHCs observed at the study site, and were responsible for 35 and 23% of the total O3 production, respectively. The preferential presence of NOx in the morning inhibited net O3 production; meanwhile O3 built up in the afternoon due to a decrease in NOx concentrations. These results indicated that a joint effort in the regulation of solvent (aromatics) usage and OBB, as well as NOx from on-road vehicle exhaust may be effective in eliminating high-O3 pollution risk in the rural areas of the YRDR.

A yellow sand transport episode from the Asian continent to Japan and North America which occurred in April 1998 is simulated. A new on-line dust tracer model coupled with a regional-scale meteorological model is developed and applied to this dust storm episode. The results for two large dust events that started during April 14–15 and 19–20, 1998, have been analyzed and discussed. The first dust storm was trapped in a cutoff vortex developed over the China plain. A modeled 3-D structure of dust associated with this cutoff vortex agreed with an observed time-height cross section of dust concentration. Results show that the strong subsidence at the backside of the vortex restricted the dust layer below 3 km level. Model analysis revealed that the second dust event that started during April 19–20 over inland China was the origin of a dust episode reported over North America. The trans-Pacific dust transport simulation successfully showed the dust onset near the West Coast of North America. Elevation of the dust layer during the long-range transport was below 3 km. The model is extended to include the transport of an Asian origin anthropogenic tracer over the North Pacific Rim. Both the natural-origin mineral dust and the Asian-origin anthropogenic tracer are simultaneously transported even if their emission regions are different.

A regional climate model, NIES/CCSR RAMS, was used with the ECMWF objective analysis data as boundary conditions to reproduce the precipitation pattern over East Asia in June, including that accompanying the Baiu front. In the control experiment, the simulated precipitation pattern was unrealistic, mainly in two respects: precipitation over the Baiu front was too weak, and strong precipitation was found over the North Pacific subtropical high at around 20°N. According to the ECMWF data, strong potential instability is maintained over the subtropical high, under which condition, the cumulus parameterization used in the model predicts strong precipitation to stabilize the atmosphere. Because the lower free atmosphere is very dry over the subtropical high, it is conjectured that the development of deep cumulus convection is suppressed by this dry air in the real atmosphere. When the cumulus parameterization was modified to include this assumption, the intensity of precipitation over the Baiu front as well as the unrealistic precipitation pattern over the subtropical high was clearly ameliorated. The intensification of precipitation over the Baiu front is considered to be due to the increased water vapor transport to the Baiu front, and the decreased stability with respect to the moist convection around the Baiu front. In semi-prognostic experiments with CCSR/NIES AGCM, this modification was found to be also effective in many other parts of the globe. Because problems in precipitation distribution similar to that discussed in the present study are found in many other climate models, the modification of cumulus parameterization suggested here could also be effective in those models.

Airborne gaseous and particulate matter in winter was measured over for 37 days in January and December 1997 at 2 sampling sites in northern Kyushu, Japan. One sampling site, Goto Island (an isolated island in the East China Sea), was about 200 km southwest of the other sampling site, Dazaifu city. In winter, acidic sulfates generated over the East Asian continent were transported to northwest Kyushu, to places such as Goto Island and the inland Kyushu area, and high sulfate concentrations were observed at the 2 sampling sites when strong NW winds blew. Acidity around Goto was mainly influenced by particulate NH4HSO4. The concentrations of NH3 at Goto Island were lower than at Dazaifu city. The difference in NH3 levels at the 2 sampling sites plays an important role in the chemical forms and sizes of the particulate matter. Nitrates at Goto Island were mostly present as NaNO3 and Ca(NO3)2 in coarse-size particles. During the process of long-range transport of air pollutants from the Asian continent to Goto, gaseous HNO3 was produced by a photochemical reactions of nitrogen oxides in the atmosphere, and particulate NaNO3 and gaseous HCl were formed by a chlorine-loss reaction between NaCl and gaseous HNO3. When strong NW winds blew, acidic sulfates together with some of the NaNO3 and/or Ca(NO3)2 and some of gaseous HCl and HNO3, which exist in the sea to the west of Kyushu and Goto Island, were transported to inland Kyushu such as Dazaifu city. During the process of transport, most of the acidic sulfates and acidic gases were mixed with regional air pollutants such as chlorides and nitrates existing around Dazaifu city, and neutralized forming (NH4)2SO4, NH4Cl and NH4NO3 in an environment of excess NH3. Therefore, the main chemical forms of NO3− at Dazaifu city varied day-by-day from fine-sized NH4NO3 to coarse-sized NaNO3 and/or Ca(NO3)2. The appearance of NO3− in coarse-size particles at Dazaifu city was due to the transport of NO3− from around the sea to the west of Kyushu.

To determine the variability of chemical properties in marine aerosols, a stationary shipboard measurement study was carried out at a station over the Northwest Pacific for 29 hours in the summer of 1999. Under a North Pacific high pressure system, carbonaceous substances, major inorganic ions, and particle numbers of typical marine aerosols were measured with little influence from continental and anthropogenic sources. The mass median diameter of organic aerosol was larger than 0.5 μm and its behavior over time was similar to sea-salt aerosol. Although the source of marine organic aerosol was believed to be mainly from continents, this result suggested that organic substances in micro layer of the sea surface is one of the sources to supply fine organic aerosol to the marine atmosphere. The further investigation would be necessary over various oceanic regions to find out the effects of marine biological activities.

`Kanpachi Street Cloud (KSC)' is an unusual small-scalecumulus cloud line visible during calm summer conditions over a major street in the Tokyo metropolitanarea. In order to understand the mechanism leading to the formation of this cloud line,numerical simulations have been performed using the Regional Atmospheric Modelling System.The general characteristics of the simulated KSC agree well with observations. On alarge-scale view, the KSC can be characterized as a cumulus cloud line generated at the convergenceline of two sea breezes on the western side of Tokyo Bay, while on the microscale view, it resemblesBenard-type thermal convection modified longitudinally by wind shear.

The satellite images of volcanic clouds in Kyushu, Japan during September–November 1989 were studied in connection with the mountain site measurement of atmospheric qualities at Unzen-Nodake and the SO2 concentration data at Aso Volcano Museum. The images strongly indicate that many high concentration events of SO2 were the results of the long-range transport of volcanic gas from Mt. Aso and Mt. Sakurajima to these stations. Brief comments on the 2000 eruption of Miyake-jima volcano are added.

Outflow patterns of air pollutants, and mechanisms associated with a monsoon condition that is peculiar to the East Asian region in winter, have been studied. To capture the continental outflow, airborne and shipboard measurements of aerosols and trace gases were conducted over the northern part of the East China Sea and the western part of the Sea of Japan on January 17-26, 1991 (airborne), January 28-29, 1992 (airborne), January 22-31, 1993 (shipboard), and January 29-30, 1993 (airborne). At least two types of highly polluted air masses were found at different times of the monsoon. Type 1 polluted air mass, which contained more than 10 μg m -3 of non-sea-salt SO 4 2- and more than 5 μgC m -3 of black carbon aerosols, typically appeared over the East China Sea at the beginning of the monsoon period. Chemical and microphysical characteristics suggest that the type 1 polluted air mass is chemically aged. Type 2 air mass appeared in the later half of the monsoon period and had characteristics of freshly emitted pollutants. It consisted of several high concentrations of SO 2 (>10 ppbv) confined in narrow horizontal width (10 to 30 km wide). Analyses using an Eulerian chemical transport model and detailed backward trajectories indicate that the type 1 polluted air mass was subcontinental in extent and its formation and the transport were dominated by a synoptic-scale weather cycle; it was formed over the Asian continent under anticyclonic conditions that persisted for 3-4 days, and transported intermittently to the east over the Pacific Ocean by the passage and the development of traveling cyclones. This study suggests that aerosols that flow out from East Asia are enriched with carbonaceous materials and consequently have low single-scattering albedo, which may affect the direct radiative forcing by aerosols over the North Pacific.

The relationship between emission intensity of (nitrogen oxides) (NO x ), NC non-methane hydrocarbons (NMHC) and O 3 concentration covering the Kanto area (Tokyo and surrounding prefectures) were investigated based on data analysis and model simulation. The observed trend in NO x concentration increased and the NMHC/NO x ratio and NMHC concentration decreased from 1978 to 1990. These emission changes will act to change the place where the maximum ozone is observed in the Kanto area. The fact is that the location of the daily maximum oxidant concentration has moved further from the emission areas. To clarify the temporal and areal distribution of photochemical air pollution in the Kanto area, the Urban Airshed Model (UAM) was applied. Assuming 25% decrease in NMHC and 50% increase in NO x emission intensities, simulation result showed almost the same maximum O 3 value compared with the base-case simulation for 1981. On the other hand, the time when the maximum value appeared changed from 1400JST to 1600JST. Higher concentrations of oxidants were usually observed near the shore in the morning, and moved inland following sea breeze penetration. Under these meteorological conditions, the time shift obtained by the UAM simulation corresponds to the observed areal shift of the daily maximum O 3 concentration.

Using observations from the Cheeka Peak Observatory in northwestern Washington State during March-April, 1997, we show that Asian anthropogenic emissions significantly impact the concentrations of a large number of atmospheric species in the air arriving to North America during spring. Isentropic back-trajectories can be used to identify possible times when this impact will be felt, however trajectories alone are not sufficient to indicate the presence of Asian pollutants. Detailed chemical and meteorological data from one of these periods (March 29th, 1997) indicates that the surface emissions were lifted into the free troposphere over Asia and then transported to North America in ∼6 days.

In the Osaka area, high concentrations of NO2 are observed in spring. To understand the relative roles and amounts of transported background ozone, photochemical ozone, transported NO2, and primary emitted NO2 in controlling NO2 formation in the Osaka area, a three-dimensional photochemical air pollution simulation model was applied based on the actual meteorological and emission conditions. Simulated results reveal that photochemical reactions play an important role in the formation of the springtime high concentrations of NO2 in Osaka.

High concentrations of nitrogen dioxide are frequently observed in the Osaka area in the spring. To clarify the mechanism of springtime air pollution formation, a series of three-dimensional field observations was conducted in April 1993 covering Osaka and the surrounding area. During the aircraft observations of 19–21 April 1993, high concentrations of photochemical air pollution were observed over the Osaka area under a stagnant meteorological condition. The maximum observed ozone concentration was more than 150 ppb. The vertical distribution of ozone was uniform up to 2400 m in the daytime. At Mt. Ikoma (600 m), the ozone level was almost constant during the afternoons of 19–20 April 1993, ranging from 80 to 100 ppb, and the presence of aged secondary pollutants was detected in the nighttime. The upper ozone concentration above 3000 m was approximately 60 ppb. The observational results, near the surface and aloft, indicate the importance of photochemically produced ozone and transported backgr...

Hourly measurements of nine C 2 –C 5 hydrocarbons (HCs) were made over a period of 15 months in the center of Osaka City, Japan. The measurements were made by using an automated system consisting of a combination of a gas preconcentrator and a gas chromatograph. The concentrations of all components were high in early winter and low in summer. The highest concentration was of C 2 H 4 , while C 3 H 6 showed the lowest concentration throughout the year, and was rarely detected in summer. There were small annual variations in the concentrations of C 4 –C 5 HC. The chemical reactions that affect HC concentrations were also examined. The seasonal C 2 H 4 /C 2 H 2 and C 3 H 6 /C 2 H 2 ratios were compared, taking into account that C 2 H 4 , C 2 H 2 , and C 3 H 6 are mainly from vehicles and the differences in their reactivities. Despite the high reactivity of C 2 H 4 , the C 2 H 4 /C 2 H 2 ratio was low in winter and high in summer, with the result that the C 2 H 4 consumption by chemical reaction seemed small in the center of the city. The behavior of C 3 H 6 /C 2 H 2 is opposite to that of C 2 H 4 /C 2 H 2 , illustrating the more reactive characteristics of C 3 H 6 . Regarding the effect of photochemical reactions, it was observed that HC’s levels drop as NO 2 /NO x increases. Though the slope does not show a direct proportionality to HC reactivity, reactivity of C 3 H 6 , which is the most reactive HC among the nine measured HCs, showed the largest declines. The ratio of C 4 –C 5 HC to the C 2 –C 5 HC rose with increase in ambient temperature, while the ratio of C 2 –C 5 HC to the nonmethane hydrocarbons decreased. This phenomenon was correlated with ambient temperature, indicating higher emissions of higher molecular weight HCs in summer.

Ozone transport and chemistry in the springtime in east Asia are studied by use of the STEM-II (Sulfur Transport Eulerian Model) regional-scale transport/chemistry model. Three-dimensional simulations are performed for the period May 1–15, 1987. This was a period of strong downward transport of ozone in east Asia, associated with traveling low-pressure systems. Elevated ozone levels were observed at high-altitude surface sites in Japan during this period. Model simulations both with and without photochemical processes are performed in order to assess the relative importance of the transport and chemical sources of tropospheric ozone. The model results are compared with measured values at a network of stations in Japan and are found to accurately capture most of the important observed features. Near-surface ozone levels are found to be strongly influenced both by continental outflow of precursors occurring behind the cold fronts as they move out over the Pacific Ocean and by the strong downward transport of ozone-rich air from the upper troposphere which occurs in association with these weather systems.

Numerical simulation of Kanpachi cloud, i. e. generated just over the Kanpachi Street under calm and clear atmospheric conditions, has been performed by RAMS (Regional Atmospheric Modeling System). The method of Four-Dimensional Data Assimilation (4DDA) and Nest Grid System, the most advanced meteorological prediction techniques, are used in this simulation.Simulated wind field and cloud in the morning predicted by the model agree very well with those of the observation by Kai et al.(1995). Additionally, the cloud line that was observed in the afternoon and a local convergent flow due to two sea breezes (one from Sagami Bay and another from Tokyo Bay) could also be simulated although the simulated cloud is rather underestimated. These numerical results suggest that Kanpachi cloud in the afternoon has some different mechanism from that in the morning such as aerosol effect of urban pollution to cloud formation.

To understand the observed characteristics of transboundary air pollutants transport over the East Asia, an atmospheric transport model which includes detailed chemical reactions, the STEM (Carmichael et al, [3]), was applied. It was found that wind pattern variations associated with a synoptic scale pressure system are extremely important for the transport of pollutants in this region. An on-line transport model coupled with Regional Atmospheric Modeling System (RAMS, Pielke et al., [9]) are also applied during the rainy season (June). On-line transport model explained well the sulfate concentration variation, and indicates that the strong concentration gradients exists at the northern side of rainy meso-front (typically at Korea and Kyushu Japan). It was found that the location of rainy meso-front plays an important role for sulfate concentration level in Japan and Korea.

Carbon monoxide (CO) emissions in China in 2005–2010 were estimated by inversion, using the Green's function method from vertical CO profiles derived from MOPITT Version 5 satellite data and a tagged CO simulation, and validated with independent in situ observations from the World Data Centre for Greenhouse Gases. Modeling with a posteriori emission successfully reproduced CO outflow from the continent to the East China Sea, Sea of Japan, and Japanese islands during winter and spring, and compensated for underestimates in central and eastern China in summer. A posteriori emissions showed large seasonal variations in which December and March emissions were on average 23% larger than August emissions, consistent with other studies. Estimated Chinese CO emissions were 184.4, 173.1, 184.6, 158.4, 157.4, and 157.3 Tg/year for 2005–2010, respectively. The decrease after 2007 is partly attributed to Chinese socioeconomic conditions and improved combustion efficiency.

This study presents an analytical investigation of the local behaviour of the solution to a mesoscale model with Newtonian nudging when observed winds are time varying. The analysis examines each Fourier component of the time series of observed winds. Unlike the case with a constant observed wind, the nudged wind vector does not asymptotically approach the observed wind. In response to sinusoidal oscillation of the observed wind, the nudged wind vector is always on a half circle connecting the vector ends of the observed and un-nudged modelled winds. When nudging parameter α→0, the nudged wind vector approaches the un-nudged wind; when α→∞, the nudged wind vector approaches the observed wind. For commonly used values of nudging parameter α, the modelled wind field always carries errors.

Despite the importance of the role of nitrogen dioxide (NO2) in tropospheric chemistry, the causes leading to the discrepancy between satellite-derived and modeled tropospheric NO2 vertical column densities (VCDs) over East Asia remain unclear. Here the reproducibility of satellite tropospheric NO2 VCD data by a regional chemical transport model (CMAQ) with the Regional Emission inventory in ASia (REAS) Version 2 is evaluated from the viewpoint of the diurnal variation of tropospheric NO2 VCDs, where satellite observations at different local times (SCIAMACHY/ENVISAT, OMI/Aura, and GOME-2/Metop-A) are utilized considering literature validation results. As a case study, we concentrate on June and December 2007 for a detailed evaluation based on various sensitivity simulations, for example with different spatial resolutions (80, 40, 20, and 10 km) for CMAQ. For June, CMAQ generally reproduces absolute values of satellite NO2 VCDs and their diurnal variations over all 12 selected diagnostic regions in East Asia. In contrast, a difficulty arises in interpreting the significant disagreement between satellite and CMAQ values over most of the diagnostic regions in December. The disagreement cannot be explained by any of the sensitivity simulations performed in this study. To address this, more investigations, including further efforts for satellite validations in wintertime, are needed.

メソスケール気象モデルとラグランジェ型粒子モデルを用いて桜島からの火山プリュームの輸送・拡散過程を解析した. 気象モデルにはナッジングによる4次元データ同化手法を利用し, 1987年5月7日から10日までの気流をシミュレートし, 火山プリュームの3次元的な輸送・拡散過程が捕えられた. 火山ガスプリュームは高度500～2000m付近を輸送され, 長崎県北部 (風下移流距離200km) で水平方向に50kmの広がりを取っていた. 上空を輸送される火山プリュームの地上への輸送には, 大気境界層の発達によるエントレイメントが重要な役割を示した. モデルの結果は同期間に行われた航空機観測結果と長崎県下の地上測定局のSO2濃度の時間空間変化をよく説明できた.

Atmospheric aerosols were collected from October 1990 to February 1992 in northern Kyushu (Tsushima and Ogori), Japan and Seoul, Korea, simultaneously using identical sampling system and chemical analysis methods. Observed data were analyzed with meteorological data to clarify the seasonal variations in aerosol concentration and composition. Dominant ion components of aerosol were SO42− in anion and NH4+ in cation. The concentrations of ion components were higher in winter than those in summer. Equivalent concentration ratio of particulate nitrate and sulfate ( NO 3 − SO 4 2− ) showed high value in Ogori having a peak in winter season. Equivalent concentration ratio of Ca2+ and sulfate ( Ca 2+ SO 4 2− ) is highest in Seoul and shows no seasonal variation. On the contrary, Tsushima and Ogori showed low value in summer season. In summer, this area is affected by the atmospheric high-pressure system which developed at the southern Kyushu sea area and southerly monsoon wind predominate. As the result of this, supply of Ca2+ from soil should be diminished in summer. Equivalent concentration ratio of particulate Cl− and Na+ ( Cl − Na + ) in August was half compared with the ratio observed in February. Episode analysis of June 1991 and February 1992 indicated the transportation of pollutants from the outside of Japan. Air masses from the Chinese continent have been concluded to bring the greatest amount of anthropogenic pollutants to Korea and Japan.

The high concentration of NO2 in the Tokyo Metropolitan area was investigated by means of air quality monitoring station data analysis and two numerical models: a photochemical box model and a photochemical grid model. Based on monitoring data, the typical variation with time of NO, NO2 and O3 for days with high NO2 concentrations is presented. The application of the photochemical box and photochemical grid models successfully reproduced these variations when using typical emission intensities for NOx and NMHC from the Tokyo downtown area. Model results revealed that the high concentrations of NO2 in winter (exceeding the Japan environmental quality standard) mainly result from photochemical oxidation of NO to NO2.

Photochemical air pollution is still a serious environmental issue in Tokyo and Osaka areas. To clarify the past trend and present status of photochemical air pollution, the annual trends of daily maximum oxidant concentration covering Kanto (Tokyo and surrounding prefectures) and Kansai (Osaka and surrounding prefectures) areas were analyzed. Trends in the photochemical air pollution and NOx and VOC precursors showed identical characteristics both in Tokyo and Osaka areas. Trends in volatile organic hydrocarbons and NOx were analyzed; NOx is incresing and NMHC/NOx ratio is decreasing in the long term over both Kanto and Kansai areas, indicating an increase in ozone forming potential and a decrease in photochemical reactivity, which may be responsible for the air pollution patterns observed in the Tokyo and Osaka areas. The location of the daily maximum oxidant concentration has moved further from the emission areas.

The surface flux calculation method proposed by Louis (1979) is extended by allowing momentum and heat to have different roughness lengths (z 0 andz T respectively). Our approach is to extend the traditional analysis by a more careful consideration of potential temperature structure near the surface. This consideration leads to a redefinition of the bulk Richardson number. For bulk transfer coefficients, our method shows a significant improvement over the original Louis method when compared with the theoretical surface-layer model applied to rough surfaces. Numerical experiments simulating sea breezes in 2D show that our extension is crucially important in simulating light wind and low humidity conditions.

[1] We expanded the variational assimilation system of a regional dust model by using size-resolved inversion. Dust emissions and particle-size distributions of a severe dust and sandstorm (DSS) in April 2005 were inversely optimized with optical measurements by the National Institute for Environmental Studies lidar network. The inversion results successfully compensated underestimates by the original model and increased the Angstrom exponent around the DSS core by 13–17%, shifting the particle-size distribution to finer. The a posteriori size distribution was distinctly different between eastern and western source regions. In the western regions, dust emissions in the 3.19 and 5.06μm size bins increased considerably, and the peak size shifted from 5.06 to 3.19 μm, whereas in the eastern regions, emissions of finer particles (bins 0.82–2.01 μm) increased. Differences in vegetation and soil type and moisture between eastern and western regions might explain the characteristics of the inverted size distribution.

In this study we developed an exploratory method to investigate the potential effect of VOC reduction from specific source categories on maximum ozone. The method is based on measurement of speciated organic compounds in air and application of chemical mass balance receptor modeling (CMB) to allocate ambient concentrations to specific source categories. This evaluation results in a sample-specific emission inventory, an estimate of the VOC emissions by source in an air mass which includes variations in source discharge not reflected in the conventional emission inventory. In addition, the CMB model in conjunction with the chemical profiles for each source, provides a basis for allocating very reactive organic components not measured in the atmosphere but contributing to O3 formation. The carbon bond reaction kinetics model (CBM-IV) is used with observed meterological conditions and the specific source contributions to predict precursor conversion to ozone. Predictions of maximum O3 using the technique for 9 days in Chicago in the summer of 1987 compared favorably with measured ground-level concentrations determined to be downwind by trajectory analysis. Source categories modeled included vehicle tailpipe exhaust, gasoline vapor, petroleum refinery emissions, architectural coatings, graphicarts, vapor degreasing, dry cleaning, and waste water treatment. The end-product is a family of control response curves which show the relationship between changes in VOC precursor emissions from each source and potential maximum ozone. The control functions for vehicle exhaust indicated that control of VOC from automobiles will be effective on some high O3 days but not on others. The method complements grid-based photochemical models in that it will allow many more control options to be investigated than would be possible due to computational constraints.

Anthropogenic SO2 emissions increased alongside economic development in China at a rate of 12.7 % yr−1 from 2000 to 2005. However, under new Chinese government policy, SO2 emissions declined by 3.9 % yr−1 between 2005 and 2009. Between 2000 and 2010, we found that the variability in the fine-mode (submicron) aerosol optical depth (AOD) over the oceans adjacent to East Asia increased by 4–8 % yr−1 to a peak around 2005–2006 and subsequently decreased by 4–7 % yr−1, based on observations by the Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA's Terra satellite and simulations by a chemical transport model. This trend is consistent with ground-based observations of the number-size distribution of aerosol particles at a mountainous background observation site in central Japan. These fluctuations in SO2 emission intensity and AOD are thought to reflect the widespread installation of fuel-gas desulfurization (FGD) devices in power plants in China because aerosol sulfate is a major determinant of the AOD in East Asia. Using a chemical transport model, we confirmed that the above-mentioned fluctuation in AOD is mainly caused by changes in SO2 emission rather than by varying meteorological conditions in East Asia. High correlation was also found between satellite-retrieved SO2 vertical column density and bottom-up SO2 emissions, both of which were also consistent with observed AOD trends. We proposed a simplified approach for evaluating changes in SO2 emissions in China, combining the use of modeled sensitivity coefficients that describe the variation of AOD with changes in SO2 emissions and satellite retrieval. Satellite measurements of the AOD above Sea of Japan marked the 4.1 % yr−1 declining between 2007 and 2010, and this correspond to the SO2 emissions from China decreased by ~9 % yr−1 between the same period.

[1] To evaluate temporal variations in nitrogen wet deposition across Japan during 1989–2008, we analyzed results of a chemical transport model (the Models-3 Community Multiscale Air Quality) and observational data. The model successfully reproduced the general patterns of spatial and temporal variations of observed NO3− wet deposition rates. Wet deposition rates of NO3− across Japan increased during 1989–2008, with rates of increase of 2–5%/yr. Sensitivity simulations indicated that the increase of NO3− wet deposition rates was mostly (61%–94%) explained by the increased emissions of atmospheric pollutants in China. Contributions of China's emissions increased from 29%–35% during 1989–1993 to 43%–61% during 2004–2008, suggesting that transboundary pollution had a large impact on NO3− wet deposition in Japan. The contribution of observed NO3− to total nitrogen wet deposition (i.e., NO3− + NH4+) increased in southwestern Japan, and currently, NO3− and NH4+ make similar contributions to nitrogen wet deposition across Japan. Interannual variation of NO3− wet deposition was further evaluated using a meteorological index, area-weighted surface pressure anomaly (ASPA). When ASPA was negative, air masses from the Asian continent were more directly transported to Japan, and NO3− concentrations across Japan became high. Thus, anomalies of NO3− concentrations were negatively correlated with ASPA. Anomalies of NO3− wet deposition rates, however, showed a weak positive correlation with ASPA, reflecting a positive correlation between anomalies in precipitation rates and ASPA. This result strongly suggests that precipitation patterns have a large impact on the interannual variation of NO3− wet deposition across Japan.

This paper presents the results of recent studies on tropospheric aerosols, including Asian dust and forest fire smoke using the NIES Lidar Network, CALIPSO/CALIOP and chemical transport models. The NIES Lidar Network is a network of two-wavelength (532nm, 1064nm) polarization (532nm) lidars in East Asia. Currently the lidars are continuously operated at about 20 locations in Japan, Korea, China, Mongolia, and Thailand, in cooperation with various research institutes and universities. The network is a part of the Asian Dust Network (ADNet), SKYNET, and the GAW Aerosol Lidar Observation Network (GALION). The data from most of the lidar stations are transferred to NIES in realtime and automatically processed to derive the attenuated backscattering coefficients at 532nm and 1064nm, the volume depolarization ratio at 532nm, and the estimated dust and spherical aerosol extinction coefficients at 532nm. The data from the network are used in various research activities on Asian dust, regional air pollution, and the effects of aerosols on climate and the environment. The data are also used for real-time monitoring (for early warning assessment) of Asian dust. The results of recent studies on long-range transport of Asian dust, optical characteristics of forest fire plumes, aerosol climatology, etc. will be described.

[1] Springtime outflow of Asian dust and air pollutants was investigated by a synergetic analysis of ground-based/space-borne Lidar observations and numerical models. We identified two prominent outflow patterns, and its occurrence frequency. Pattern I was induced within a typical warm-sector which lifted up dust particles into the free troposphere, and the existence of two sequential low-pressure systems played an important role. Pattern II was a ‘behind cold front’ outbreak. Atmospheric stratification was significantly different; Pattern I had weak stratification within the troposphere (potential temperature gradient of ∼2–3.4 K/km), and most of elevated dust layer (typically horizontally 1500–2000 km, vertically 2.5–4 km AGL) remained unmixed with pollutants. Pattern II was characterized by a strong stratification of ∼5 K/km; dust and pollutants were trapped and well mixed within the PBL, forming ‘polluted’ dust. Among the six cases of large-scale dust/pollutants outbreaks, only two cases are belonged to Pattern I.

[1] In mid-August 2009, ground-based lidar networks on both sides of the Pacific Basin detected an elevated dust layer. A combined analysis by ground-based lidars, space-borne lidar CALIOP, and numerical models revealed that dust particles emitted in the Taklimakan Desert were transported across the Pacific Ocean in 12 to 13 days. This was the first evidence of summertime trans-Pacific transport of Asian dust from the Taklimakan Desert. A large-scale dust storm occurred in the Taklimakan Desert during 12–16 August due to a strong surface wind accompanied by a cold front. Many dust particles were lifted up into the free atmosphere by the upslope wind formed by the steep slope of the surrounding mountains. This dust injection process was analogous to that for springtime cases. The Taklimakan dust was then transported eastward at 6–8 km altitude. This high transport altitude allowed the Taklimakan Dust to be transported beyond the Pacific Ocean without the effect of the southeasterly outflow of the summertime Pacific high. The wind field anomaly at 500 hPa in mid-August 2009 shows increases of northwesterly winds driven by SE–NW pressure gradients around 110–140°E and 180–140°W, indicating that the pressure pattern during the dust event favored the trans-Pacific transport.

The acidity of precipitation has been observed at stations of the Acid Rain Monitoring Network run by the China Meteorological Administration (CMA-ARMN) since 1992. Previous studies have shown that different long-term trends exist in different regions but detailed analysis of the causes of these is lacking. In this paper, we analyze summertime precipitation acidity data from the CMA-ARMN during 1992–2006 using EOFs and show that the summertime pH in China had different trends before and after 2000. The most significant decrease of pH is found in Central China. To investigate the causes of this decrease of pH in summer, we explore the relationship between changes in the pH value, the East Asian summer monsoon index, rainfall data, and pollutants emissions. We find that the East Asian summer monsoon can significantly affect the acidity of summer precipitation in Central China. In strong monsoon years, the pH in Central China is about 0.33 lower than that in weak monsoon years. Chemical transport model simulations using fixed emissions indicate that about 65% of the pH value difference (i.e., 0.22) is related to the summer monsoon, and constitutes 18–36% of the observed pH change (0.6–1.2) in Central China during 1992–2006. Further studies reveal a teleconnection between the pH in Central China and the rainfall in the middle and lower reaches of the Yangtze River (MLYR), which can explain about 24% of the variance of pH in Central China. Simulations using an annually varying emission inventory show that at least 60% of the variation in precipitation acidity in Central China can be attributed to changes in pollutant emissions. Therefore, the increase in emissions of acidic species is the most important cause for the observed decrease of pH in Central China, and changes in meteorological factors, such as rainfall and other parameters related to the East Asian summer monsoon, play a less important but still significant role.

The turbulence properties of the nocturnal urban boundary layer (UBL) and its transition to the convective mixed layer have been observed over the urban center of Sapporo, Japan. The nocturnal UBL was characterized by an elevated inversion layer and a near-neutral mixed layer below it. The inversion layer varied with time and showed a wavy pattern. Kelvin-Helmholtz instability (billow) was observed within the elevated inversion layer, the horizontal and vertical scales of this billow being evaluated to be of the order of the vertical scale of the elevated inversion layer. The transition from the nocturnal UBL to the convective mixed layer occured rapidly, within 1–1.5 h over the center of the urban area. At this time, the downward transport of sensible heat below the inversion base became important. The normalized turbulence intensities in the convective mixed layer were also examined.

[1] The current debate about the role of anthropogenic pollutants in a unique broad summer maximum pattern at a remote site (Waliguan, 3810 asl) on the northern edge of the Tibetan Plateau is continuing. This study quantifies the impacts of anthropogenic emissions and stratosphere-to-troposphere exchange (STE) on surface ozone on the Tibetan Plateau using a regional chemical transport model with an on-line tracer tagging module. The model is shown to be well suited for simulating the unique seasonal variation at Waliguan. Model results clearly show that the regional transport of photochemically produced ozone in China is responsible for the summer maximum on the northern Tibetan Plateau with a contribution of ∼10–25 parts per billion by volume (ppbv) in summer, which is more than ∼5 ppbv of the contribution to STE. The weak local ozone photochemical production (−0.5–0.1 ppbv/day) suggests that this transport to the Tibetan Plateau mostly concentrates on photochemical products. The unique strong near-surface convergence and upper layer divergence driven by elevated surface heating and low air density over the Tibetan Plateau in summer is its dynamic cause. These transported anthropogenic pollutants are likely to rise to the upper troposphere and circulate globally. This study also demonstrates that the effect of convection on surface ozone over the northern Tibetan Plateau is compensated by the advective updrafts in summer.

Weighted least-squares fitting of 17 hydrocarbons was used to estimate ambient contributions from four source categories. The data set consisted of 192 samples collected from 300 to 1500 m over Tokyo, July 16-17, 1981. Six runs (flights), 1-1.5 h long, spaced throughout each day, constituted chemical snapshots of the urban air. Vehicles contributed 7.0%, gasoline vapor 10.5%, petroleum refinery 26.0%, paint solvents 27.2%, and unexplained sources 29.3% of the total hydrocarbon concentration (based on the 17 components measured and all samples). These coefficients are only representative of the days and conditions sampled and should not be interpreted as annual emission fractions. On a run-averaged basis the correlation between refinery emissions per hour, adjusted for dispersions, and ambient concentrations of total hydrocarbon attributable to petroleum refineries was r/sup 2/ = 0.899, indicating that the refinery profile was sufficiently unique to be sensed up to 70 km. The fractions for paint solvents, gasoline vapor, and unidentified sources were also consistent with wind trajectory observations. 20 references, 4 figures, 8 tables.

[1] We examine springtime ozone trends at nine remote locations in Japan during the last decade. The observed decadal ozone trends are relatively small at surface sites but are substantially larger at a mountainous site. We use a regional chemistry-transport model to explore the observed changes and how changes in Asian anthropogenic emissions have contributed to the observed increasing trends. The model with yearly-dependent regional emissions successfully reproduces the levels, variability, and interannual variations of ozone at all the surface sites. It predicts increasing trends at the mountainous site, suggesting that increasing Asian anthropogenic emissions account for about half the observed increase. However, the discrepancy between the observation and model results after 2003 (the time of largest emission increase) suggests significant underestimation of the actual growth of the Asian anthropogenic emissions and/or incompleteness in the modeling of pollution export from continental Asia.

An intense dust storm occurred during 19–20 May 2007 over the Taklimakan Desert in northwestern China. In the following days, the space-borne lidar CALIOP tracked an optically thin, highly elevated, horizontally extensive dust veil that was transported intercontinentally over the eastern Asia, Pacific Ocean, North America, and Atlantic Ocean. A global aerosol transport model (SPRINTARS) also simulated the dust veil quite well and provided a 3-D view of the dust intercontinental transport. The SPRINTARS simulation revealed that the dust veil travels at 4–10 km altitudes with a thickness of 1–4 km along the isentropic surface between 310 K and 340 K. The transport speed is about 1500 km/d. The estimated dust amounts exported to the Pacific is 30.8 Gg, of which 65% is deposited in the Pacific and 18% is transported to the North Atlantic. These results imply that the dust veil can fertilize the open oceans, provide background dust to the atmosphere remote from the sources. The entrainment mechanism that injects dust particles into the free atmosphere is important for understanding the formation of the dust veil and the subsequent long-range transport. We used a regional dust transport model (RC4) to analyze the dust emission and entrainment over the source region. The RC4 analysis revealed that strong northeasterly surface winds associated with a low pressure invade into the Taklimakan Desert through the east side corridor and form a strong up-slope wind along the high and steep mountainside of the Tibetan Plateau, blowing up large amounts of dust into the air. The updraft further brings the lofted dust particles up to the free troposphere (about 9 km MSL) where the westerly generally blows. The peculiar terrain surrounding the Taklimakan Desert plays the key role in the entrainment of dust to the free troposphere to form the dust veil.

Detailed 3-D structures of Trans-Pacific Asian dust transport occurring during 5–15 May 2007 were investigated using the NASA/CALIOP vertical-resolved measurements and a three-dimensional aerosol model (SPRINTARS). Both CALIOP and SPRINTARS dust extinctions showed a good agreement along the way of the transport from the dust source regions across North Pacific into North America. A vertically two-layered dust distribution was observed over the northeastern Pacific and North America. The lower dust layer originated from a dust storm generated in the Gobi Desert on 5 May. It was transported at an altitude of around 4 km MSL and has mixed with Asian anthropogenic air pollutants during the course of transport. The upper dust layer mainly originated from a dust storm that occurred in the Taklimakan Desert 2–3 days after the Gobi dust storm generation. The upper dust cloud was transported in higher altitudes above the major clouds layer during the Trans-Pacific transport. It therefore has remained unmixed with the Asian air pollutants and almost unaffected by wet removal. The decay of its concentration level was small (only one-half after its long-distance transport crossing the Pacific). Our dust budget analysis revealed that the Asian dust flux passing through the longitude plane of 140° E was 2.1 Tg, and one third of that arrived North America. The cases analyzed in this study revealed that, while the Gobi Desert is an important source that can contribute to the long-range dust transport, the Taklimakan Desert appears to be another important source that can contribute to the dust transport occurring particularly at high altitudes.

Observations of tropospheric aerosols (mineral dust, air-pollution aerosols, etc.) and clouds are being conducted using a network of two-wavelength (1064nm, 532nm) polarization (532nm) lidars in the East Asian region. Currently, the lidars are operated continuously at 23 locations in Japan, Korea, China, Mongolia and Thailand. A real-time data processing system was developed for the network, and the data products such as the attenuated backscatter coefficients and the estimated extinction coefficients for non-spherical and spherical aerosols are generated automatically for online network stations. The data are used in the real-time monitoring of Asian dust as well as in the studies of regional air pollution and climate change.

[1] Vertical dust structures and meteorological conditions over the Taklimakan Desert during the summertime periods (July–September) in 2006 and 2007 were investigated using satellite data including the CALIPSO lidar (CALIOP) measurements and the Weather Research and Forecasting (WRF) model simulation. Summertime convective velocity simulated by WRF was greater than 3 m/s, and the convective time scale was about 1000 s (ca. 15 min). We examined 42 CALIPSO paths (24 daytime and 18 nighttime paths) of data acquired under convective dusty conditions. The dust layer thickness derived from the CALIOP measurements reaches 3000–4000 m, which is approximately equal to the Tarim Basin depth. This thickness shows a good correlation with the WRF simulated depth of the convective boundary layer (BL). The dust remains suspended during both daytime and nighttime; the CALIOP average dust extinction coefficients in the BL are respectively 0.151 ± 0.102 km−1 and 0.128 ± 0.079 km−1 for daytime and nighttime. Finally, we estimated the dust amount transported from the BL to the free atmosphere. Typically, 10–20 Gg/day of dust (assuming area of 600 km × 300 km as a main part of the Taklimakan Desert) is transported from the Taklimakan Desert by vertical mixing. The daily horizontal dust flux above the BL was estimated to be 40–50 Gg/day over the Taklimakan Desert.

Long-term simulations of surface ozone (O3) over East Asia during 1980–2020 were conducted using the regional scale chemical transport model (CMAQ) and the newly developed year-by-year emission inventory in Asia (REAS). The CMAQ with the REAS could reproduce the spatial and seasonal variations of the observed surface O3 concentrations in 2000 and 2001. The historical simulation from 1980 to 2003 demonstrates that an annually-averaged concentration of surface O3 over the Central East China (CEC) and Japan increases about 12 ppbv (1% year−1) and 5 ppbv (0.4% year−1) during a quarter century, respectively. This simulated trend in Japan generally agrees with the observed trend measured at monitoring stations and is correlated with the trend of Chinese NOx and NMVOC emissions. The future emissions up to 2020 were projected based on three emission scenarios (PSC, REF, and PFC). In 2020, the Chinese NOx emissions in each scenario are expected to increase by −1% (PSC), +40% (REF), and +128% (PFC) from 2000, respectively. The worst scenario (PFC) shows that the East Asian NOx emissions almost double between 2000 and 2020. We find that the surface O3 concentrations in East Asia will increase significantly in the near future due to projected increases in NOx emissions.