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Observation of the ambient aerosol surface area concentrations is important to understand the aerosol toxicity because an increased surface area may be able to act as an enhanced reaction interface for certain reactions between aerosol particles and biological cells, as well as an extended surface for adsorbing and carrying co-pollutants that are originally in gas phase. In this study, the concentration of aerosol surface area was measured from April 2015 to March 2016 in Fukuoka, Japan. We investigated the monthly and diurnal variations in the correlations between the aerosol surface area and black carbon (BC) and sulfate concentrations. Throughout the year, aerosol surface area concentration was strongly correlated with the concentrations of BC, which has a relatively large surface area since BC particles are usually submicron agglomerates consisting of much smaller (tens of nanometers) sized primary soot particles. The slopes of the regression between the aerosol surface area and BC concentrations was highest in August and September 2015. We presented evidence that this was caused by an increase in the proportion of airmasses that originated on the main islands of Japan. This may enhance the introduction of the BC to Fukuoka from the main islands of Japan which we hypothesize to be relatively fresh or “uncoated”, thereby maintaining its larger surface area.

The emission characteristics of refractory black carbon (rBC) from biomass burning are essential information for numerical simulations of regional pollution and climate effects. We conducted combustion experiments in the laboratory to investigate the emission ratio and mixing state of rBC from the open burning of wheat straw and rape plants, which are the main crops cultivated in the Yangtze River Delta region of China. A single particle soot photometer (SP2) was adopted to measure rBC-containing particles at high temporal resolution and with high accuracy. The combustion state of each burning case was indicated by the modified combustion efficiency (MCE), which is calculated using the integrated enhancement of carbon dioxide and carbon monoxide concentrations relative to their background values. The mass size distribution of the rBC particles showed a perfect Gaussian shape with an average mass equivalent diameter (MED) of 189 nm (the measured MED values varied between 152 nm and 215 nm), assuming an rBC density of 1.8 g/cm3. rBC particles less than 80 nm in size (the lower detection limit of the SP2) accounted for only ~ 5 % of the total rBC mass, on average. The emission ratios, which are expressed as ∆rBC/∆CO (∆ indicates the difference between the observed and background values), displayed a significant positive correlation with the MCE values and varied between 1.8–34 ng/m3/ppbv. Multi-peak fitting analysis of the delay time (∆t, or the time of occurrence of the scattering peak minus that of the incandescence peak) distribution showed that rBC-containing particles with rBC MED = 200 ± 10 nm displayed two peaks at ∆t = 1.7 μs and ∆t = 3.2 μs, which could be attributed to the contributions from both flaming and smoldering combustion in each burning case. Both the ∆t values and the shell/core ratios of the rBC-containing particles clearly increased as the MCE decreased from 0.98 (smoldering-dominant combustion) to 0.86 (flaming-dominant combustion), implying the great importance of the rapid condensation of semi-volatile organics. This study highlights that open biomass burning produces the majority of coated rBC particles, which have considerable ability to affect cloud processes and influence regional climate.

Mass concentrations of chemical compounds in both PM2.5 (particle aerodynamic diameter, Dp

A long-lasting high particulate matter (PM) concentration episode persisted over East Asia from May 24 to June 3, 2014. The Nested Air Quality Prediction Model System (NAQPMS) was used to investigate the mixing of dust and anthropogenic pollutants during this episode. Comparison of observations revealed that the NAQPMS successfully reproduced the time series PM2.5 and PM10 concentrations, as well as the nitrate and sulfate concentrations in fine (aerodynamic diameter ≤ 2.5 μm) and coarse mode (2.5 μm

Satellite observations of the tropospheric NO2 vertical column density (VCD) are closely correlated to, and thus can be used to estimate, surface NOx emissions. In this study, the NO2 VCD simulated by a regional chemical transport model with emissions data from the updated Regional Emission inventory in ASia (REAS) version 2.1 were validated through comparison with multisatellite observations during the period 2000–2010. Rapid growth in NO2 VCD (~11% year−1) driven by the expansion of anthropogenic NOx emissions was identified above the central eastern China (CEC) region, except for the period during the economic downturn. In contrast, slightly decreasing trends (~2% year−1) were identified above Japan accompanied by a decline in anthropogenic emissions. To systematically compare the modeled NO2 VCD, we estimated sampling bias and the effect of applying the averaging kernel information, with particular focus on the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) data. Using the updated REAS, the modeled NO2 VCD reasonably reproduced annual trends observed by multisatellites, suggesting that the rate of increase of NOx emissions estimated by the updated REAS inventory would be robust. Province-scale revision of emissions above CEC is needed to further refine emission inventories. Based on the close linear relationship between modeled and observed NO2 VCD and anthropogenic NOx emissions, NOx emissions in 2009 and 2010, which were not covered by the updated REAS inventory, were estimated. NOx emissions from anthropogenic sources in China in 2009 and 2010 were determined to be 26.4 and 28.5 Tg year−1, respectively, indicating that NOx emissions increased more than twofold between 2000 and 2010. This increase reflected the strong growth of anthropogenic emissions in China following the rapid recovery from the economic downturn from late 2008 until mid-2009. Our method consists of simple estimations from satellite observations and provides results that are consistent with the most recent inventory of emissions data for China.

Determining the source contributions of tropospheric ozone concentration is an important issue for East Asia, due to the dramatic and rapid increase in emissions of atmospheric pollutants. To achieve this, the higher-order decoupled direct method (HDDM), a technique for efficient calculation of sensitivities, was applied in this study. Tropospheric ozone concentrations at observation sites located in remote areas of Japan were well-reproduced by Community Multi-scale Air Quality (CMAQ) model simulations, and exhibited a maximum peak in spring, a relatively small peak in autumn and a summer minimum. This seasonal pattern is a reflection of long-range transport and chemical processes, coupled with continental-oceanic air mass exchanges forced by the East Asian monsoon. For the HDDM simulation, we focused on episodic pollution events during each season of 2007 to clarify the seasonal characteristics, and then assessed source contributions paying attention to both precursor emissions (NOx and VOC) and source regions (China, central eastern China, Korea, and Japan). An ozone-sensitive regime (NOx- or VOC-sensitive regime) was also determined based on the HDDM results. This suggested a regime over East Asia that was NOx sensitive in summer, VOC sensitive in winter, and either NOx or VOC sensitive during spring and autumn. At observation sites in remote areas of Japan, by separating the precursor contribution into NOx and VOC components of ozone production, it was found that the contribution of NOx emissions was larger than that of VOC emissions in spring, autumn, and especially summer, therefore, a reduction in NOx emissions could reduce the severity of episodes of tropospheric ozone pollution in downwind areas. Due to the strong VOC-sensitive conditions in winter, NOx emissions enabled a reduction in surface ozone concentrations. In terms of the contributions attributed to source regions, the source contribution of China was relatively high during spring, but local-scale photochemical build-up was dominant during summer and autumn. It was also revealed that central eastern China (CEC), characterized by densely populated and industrialized regions, was the most significant source of Chinese source contributions in summer.

Five years of CALIPSO lidar layer products are used to study transpacific transport of Asian dust. We focus on possible changes to dust intrinsic optical properties during the course of transport, with specific emphasis on changes to particulate depolarization ratio (PDR). PDR distributions for Asian dust transported across the Pacific are compared to previously reported PDR distributions for African dust transported across the Atlantic. African dust shows a slight decreasing trend in PDR during westward transport across the Atlantic during its most active long-range transport season in summer. Asian dust, on the other hand, shows some spatial variability in PDR over the Pacific during its most active long-range transport season in spring. The dust PDR is generally smaller over the ocean than over the Tarim basin and nearby downwind regions. PDR also shows a decreasing trend with latitude moving northward toward the Arctic, together with an increasing trend in the dust aerosol optical depth (AOD) when passing over polluted Asian regions. Possible explanations include (i) the mixing of dust externally or internally with other types of aerosol over the heavily developed industrial regions in East Asia, and (ii) the downstream mixing of dust plumes from different source regions (i.e., Tarim and Gobi). Dust from different source regions exhibits relatively large differences in PDR, with mean values of 0.34±0.07, 0.28±0.06, and 0.30±0.08, respectively, over the Tarim basin, Gobi Desert and Northwest African source regions. Different transport mechanisms are seen for African dust and Asian dust. Asian dust transport is originated by cold fronts and driven by westerly jets. In contrast, summer African transatlantic dust transport is driven by trade winds and is generally well confined in altitude in the free troposphere throughout the tropics and subtropics.

Long-term (2009–2015) observations of atmospheric black carbon (BC) mass concentrations were performed using a continuous soot-monitoring system (COSMOS) at Fukue Island, western Japan, to provide information on wet removal rate constraints and the emission strengths of important source regions in East Asia (China and others). The annual average mass concentration was 0.36 µg m−3, with distinct seasonality; high concentrations were recorded during autumn, winter, and spring, and were caused by Asian continental outflows, which reached Fukue Island in 6–46 hours. The observed data were categorized into two classes, i.e., with and without a wet removal effect, using the accumulated precipitation along a backward trajectory (APT) for the last 3 days as an index. Statistical analysis of the observed ΔBC/ΔCO ratios was performed to obtain information on the emission ratios (from data with zero APT only) and wet removal rates (including data with non-zero APTs). The estimated emission ratios (5.2–6.9 ng m−3 ppb−1) varied over the six air mass origin areas; the higher ratios for South Central East China (30–35° N), South China (< 30° N), and Korea than for the other areas, i.e., Northeast China (> 40° N), North Central East China (35–40° N), and Japan, indicated the relative importance of domestic emissions and/or biomass burning sectors. The significantly higher BC/CO emission ratios adopted in the bottom-up Regional Emission inventory in Asia (REAS) version 2 (8.3–23 ng m−3 ppb−1) over Central East China and Korea needed to be reduced at least by factors of 1.3 and 2.8 for Central East China and Korea, respectively, but the ratio for Japan was reasonable. The wintertime enhancement of the BC emission from China, predicted by REAS2, was verified for air masses from South Central East China, but not for those from North Central East China. Wet removal of BC was clearly identified as a decrease in the ΔBC/ΔCO ratio against APT. The transmission efficiency (TE), defined as the ratio of the ΔBC/ΔCO ratio with precipitation to that without precipitation, was fitted reasonably well by a stretched exponential decay curve against APT; a single set of fitting parameters was sufficient to represent the results for air masses originating from different areas. An accumulated precipitation of 15.0 ± 3.2 mm halved the BC mass concentration. BC-containing particles traveling to Fukue must have already been converted from hydrophobic to hydrophilic particles, because the behavior of TE against APT was similar to that of PM2.5, the major components of which are hydrophilic. After correcting for the wet removal effect, trends in the BC mass concentrations were almost flat for the air masses from CEC and Korea and decreasing for those from Japan during 2009–2015. This long-term data set will provide a benchmark for testing chemical transport/climate model simulations covering East Asia.

We used a chemical transport model to investigate the long-term trends of sulfur deposition in East Asia during 1981–2005. The model reproduced the observed spatial distributions in East Asia of the rate of wet deposition of non-seasalt sulfate (nss-SO42−), volume-weighted mean concentrations of nss-SO42− in precipitation, precipitation, and concentrations in air of gaseous sulfur dioxide and particulate nss-SO42−. The model also reproduced well observed seasonal variations and long-term trends of wet deposition of nss-SO42− in Japan from 1988 to 2005. The increasing rate of wet deposition of nss-SO42− in Japan during 1991–2005 was demonstrated with 99.9% significance for both observed and modeled data. The annual rate of total (wet + dry) sulfur deposition in Japan increased from 15.6 Gmol S y−1 in 1981–1985 to 23.9 Gmol S y−1 in 2001–2005 in response to both increasing contributions from Chinese emissions and the eruption of Miyakejima volcano in 2000. During that 25-year period, approximately 2.1% of the sulfur from Chinese emissions was deposited in Japan. Over the same period, the rate of deposition of sulfur in East Asia increased gradually from 14.2 mmol S m−2 y−1 to 24.0 mmol S m−2 y−1, and the contribution of emissions from China to total sulfur deposition in East Asia increased from 65% to 77%. The contribution of Miyakejima volcano was 3% during 2001–2005. The increase in the sulfur deposition rate was remarkably high on the North China Plain, around Guangzhou, and south of Chongqing. The rate of increase in East Asia was greatest in winter, although the rate of sulfur deposition was highest in summer. Sulfur flux from China to Japan increased by a factor of 2.5 at altitudes of 0–3000 m from 1981 to 2005.

To illuminate the issue of trans-boundary O 3 pollution and regional O 3 reduction policies in East Asia, we have investigated the East Asian ozone (O 3 ) response to perturbations caused by Chinese anthropogenic emissions using the Community Multiscale Air Quality (CMAQ) model, a regional chemical transport model. The O 3 responses have been examined for the range between −100 and +100% changes from the Chinese emissions level in 2004 in 10% intervals. We have found that springtime and summertime O 3 responses both at the source and at the downwind areas can be regarded as linear over the range between −30 and +100% changes from the current emissions level. We therefore suggest that the perturbation between −30 and +100% is sufficiently small to avoid nonlinear chemical influence on O 3 formation in a model experiment to investigate East Asian scale O 3 source-receptor relationships. On the other hand, the O 3 response is strongly nonlinear in April at Hong Kong, where the current NMVOCs/NO x ratio is low and the O 3 production regime is easily moved to the NMVOCs sensitive region. The O 3 responses to the NO x emission changes have been investigated using surface O 3 concentrations at remote Japanese sites and tropospheric NO 2 vertical column density (NO 2 VCD) over central east China both with observations and with model simulations in springtime during 2003–2009. Analysis of satellite data shows that the observed range of NO 2 VCD over central east China in 2003–2009 is the range between −25 and +34% from the 2004 level, which corresponds approximately to an emission variation between −21 and +29%. The O 3 concentration in the downwind region during 2003–2009 responds linearly to a change of the NO 2 VCD over central east China both in the model and in the observation. The corresponding O 3 responses derived from surface observations at remote Japanese sites show linear features consistent with this expectation. The doubling of emissions, i.e., approximately 1.9-fold increase in the NO 2 VCD from 2004, leads to O 3 increments of 5 ppbv and 8 ppbv in the model and in the observation, respectively. The modeled O 3 increase due to changes in NO x emission explains approximately 60% of the observed O 3 trend at remote Japanese sites. Thus, approximately 40% of the observed O 3 increase is unaccounted for by the NO x emissions growth.

We applied the decoupled direct method (DDM), a sensitivity analysis technique for computing sensitivities accurately and efficiently, to determine the source-receptor relationships of anthropogenic SO(2) emissions to sulfate aerosol over East Asia. We assessed source contributions from East Asia being transported to Oki Island downwind from China and Korea during two air pollution episodes that occurred in July 2005. The contribution from China, particularly that from central eastern China (CEC), was found to dominate the sulfate aerosols. To study these contributions in more detail, CEC was divided into three regions, and the contributions from each region were examined. Source contributions exhibited both temporal and vertical variability, largely due to transport patterns imposed by the Asian summer monsoon. Our results are consistent with backward trajectory analyses. We found that anthropogenic SO(2) emissions from China produce significant quantities of summertime sulfate aerosols downwind of source areas. We used a parametric scaling method for estimating anthropogenic SO(2) emissions in China. Using column amounts of SO(2) derived from satellite data, and relationships between the column amounts of SO(2) and anthropogenic emissions, 2009 emissions were diagnosed. The results showed that 2009 emissions of SO(2) from China were equivalent to 2004 levels.

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 3–8% yr−1 to a peak around 2005–2006 and subsequently decreased by 2–7% 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 aerosol particles at a mountainous background observation site in central Japan. These fluctuations in SO2 emission intensity and fine-mode 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 fine-mode AOD in East Asia. Using a chemical transport model, we confirmed that the contribution of particulate sulfate to the fine-mode AOD is more than 70% of the annual mean and that the abovementioned fluctuation in fine-mode AOD is caused mainly by changes in SO2 emission rather than by other factors such as varying meteorological conditions in East Asia. A strong correlation was also found between satellite-retrieved SO2 vertical column density and bottom-up SO2 emissions, both of which were also consistent with observed fine-mode AOD trends. We propose a simplified approach for evaluating changes in SO2 emissions in China, combining the use of modeled sensitivity coefficients that describe the variation of fine-mode AOD with changes in SO2 emissions and satellite retrieval. Satellite measurements of fine-mode AOD above the Sea of Japan marked a 4.1% yr−1 decline between 2007 and 2010, which corresponded to the 9% yr−1 decline in SO2 emissions from China during the same period.

The NASA space-borne Mie-lidar system CALIPSO/CALIOP revealed that multiple large Asian dust layers with a horizontal scale of 2000–3000 km reached North America, occupying the full troposphere, in April 2010. This kind of dust layer transport has not been reported before. Our analysis of CALIOP data and global aerosol model results revealed that frequent dust emissions occurred in northwestern China because of stronger-than-average near-surface winds, and that strong stable westerly winds carried the Asian dust from northwestern China to the central Pacific Ocean. A negative pressure anomaly was located in the eastern Pacific Ocean, and the main dust transport path was split into two branches: a northern path and a southern path over North America. Northern-path dust was trapped and stagnant for a longer time than southern path dust and finally subsided under a high pressure system. Dust along the southern path reached the central US. These complex conditions resulted in a multi-layered structure of dust over North America.

Mount Kilauea in the Hawaiian Islands experienced an active eruption from March until the end of December 2008 and showed a large-scale impact on aerosol, cloud microphysical properties and atmospheric radiation over the North Pacific. We analyzed the atmospheric impact of this eruption based on the satellite retrievals and 3-D global chemistry-radiation coupled transport model. We showed that approximately 1.8 Tg (±1.2 Tg) release of SO2 was estimated from this eruption, which oxidized into sulfate aerosol during transport to the northwest Pacific Ocean. The volcanic sulfate aerosol layer covering a large area (∼6.5 × 106 km2) of the lower troposphere over the North Pacific for several months was confirmed from both satellite and model results. Sulfate aerosols affected the formation of cumulus water clouds by reducing the typical cloud effective radius by ∼23% and increasing the cloud fractional coverage over the ocean from 9.1% to 13.4% (over the region 170°E-160°W, 10°N-20°N). The affected cumulus clouds appeared whiter than normal and thus reflected more solar radiation. Consequently, satellite observations revealed an approximately 1% increase in albedo at the top of the atmosphere in the area along main volcano plume trajectory, which induced an approximately -5 W m-2 change in the shortwave radiation budget.

As one of research activities of the Joint Research on Dust and Sand Storms (DSS) among China, Korea and Japan, intercomparison between two operational dust forecasting models (ADAM and CFORS/Dust) has been conducted using the selected DSS case which occurred in 2007. The results of simulations by both models were compared with various observations such as surface PM10, Aerosol Optical Thickness, and dust extinction coefficient. In general, both models produced similar results and the predicted values matched well with the observations, despite differences in emission treatment, the adoption of data assimilation technique, and meteorological inputs. However, a large difference (up to 4 times) in modeled surface PM10 concentrations between the models was observed at sites located in source or near-source regions. For the selected case, the dust emission amount calculated by ADAM was larger than that by CFORS/Dust. The vertical structure of dust layer from the models was different due to the characteristics of meteorological inputs used for each model. This study suggests that the construction of more accurate dust source allocation scheme, comprehensive dust emission treatment, improved meteorological inputs and the development of dust data assimilation technique with various dust observations are required for building a more accurate early-warning system of DSS in East Asia.

Surface observation data taken in Mongolia, China, Korea and Japan during the Asian dust event of March 29 to April 2, 2007 were compared with a regional dust transport model assimilated with the lidar network data. The assimilated model reproduced the reported dust event in Mongolia and the observed PM10 concentrations in Korea and Japan very well. The mass/extinction conversion factor (MEF) obtained from the lidar dust extinction coefficient and PM10 concentration was also compared with the assimilated model for Seoul and Tsukuba where both the lidar and PM10 data were available. The MEFs for PM10 and PM2.5 (the ratio of dust-only PM10 or PM2.5 to the dust extinction coefficient) were calculated with the assimilated model. The modeled MEF for PM10 reproduced the observed MEF reasonably and exhibited spatial and temporal variations reflecting the variations in the dust particle size distribution. The modeled MEF for PM2.5 had much less variation. This indicates that the dust extinction coefficient has a higher correlation with dust PM2.5 and should be a useful index for studying the effect of dust on human health.

The impact of open crop residual burning (OCRB) on O3, CO, black carbon (BC) and organic carbon (OC) concentrations over Central Eastern China (CEC; 30–40° N, 111–120° E), during the Mount Tai Experiment in 2006 (MTX2006) was evaluated using a regional chemical transport model, the Models–3 Community Multiscale Air Quality Modeling System (CMAQ). To investigate these pollutants during MTX2006 in June 2006, daily gridded OCRB emissions were developed based on a bottom-up methodology using land cover and hotspot information from satellites. This model system involving daily emissions captured monthly–averages of observed concentrations and day-to-day variations in the patterns of O3, CO, BC and OC at the summit of Mount Tai (36° N, 117° E, 1534 m a.s.l., Shandong Province of the People's Republic of China) with high correlation coefficients between the model and observations ranging from 0.55 to 0.69. These results were significantly improved from those using annual biomass burning emissions. For monthly-averaged O3, the simulated concentration of 80.8 ppbv was close to the observed concentration (81.3 ppbv). The MTX2006 period was roughly divided into two parts: 1) polluted days with heavy OCRB in the first half of June; and 2) cleaner days with negligible field burning in the latter half of June. Additionally, the first half of June was characterized by two high-pollution episodes during 5–7 and 12–13 June, separated by a relatively cleaner intermediate period during 8–10 June. In the first high-pollution episode, the model captured the high O3, CO, BC and OC concentrations at the summit of Mount Tai, which were associated with OCRB over southern CEC and subsequent northward transport. For this episode, the impacts of OCRB emissions on pollutant concentrations were 26% (O3), 62% (CO), 79% (BC) and 80% (OC) at the summit of Mount Tai. The daily OCRB emissions were an essential factor in the evaluation of these pollutants during MTX2006. These emissions have a large impact not only on primary pollutants but also on secondary pollutants, such as O3, in the first half of June over northeastern Asia. The model reproduced reasonably well the variation of these pollutants in MTX2006, but underestimated daily averages of both CO and BC by a factor of 2, when using emission data from almost solely anthropogenic fuel sources in the latter half of the observation period when field burning can be neglected.

Dust emission estimated with a 4D-Var data assimilation system using ground-based lidar network data was compared with vegetation growth data based on visual observations in the Gobi desert in Mongolia in the spring of 2007. The dust emission flux estimated with the data assimilation system was less than that estimated without data assimilation in the dust event of May 21-30 and was the opposite in the event of March 25-April 3. The threshold surface friction velocity estimated from the results of the data assimilation was less than 0.3 m s-1 in the dust event of March 25-April 3 and was ∼0.36 m s-1 in the event of May 21-30. The difference between the two events was qualitatively explained by the vegetation growth data. The accumulated precipitation during the period was ∼2 mm. The results show that vegetation growth with slight precipitation in the Gobi desert may significantly reduce dust emission.

Rapid Asian economic development might engender secondary impacts of atmospheric aerosol particles over the western Pacific after conversion of gaseous pollutants such as SO2. To elucidate changes in aerosol concentrations in leeward areas undergoing remarkable industrialization, the number-size distributions of submicrometer (0.3–1.0 μm) aerosols were measured at Murododaira (36.6° N, 137.6° E, 2450 m a.s.l.) on the western flank of Mount Tateyama in central Japan during January 1999–February 2009. Nighttime data obtained from 2400 to 0500 were used to analyze free-tropospheric aerosol concentration. Monthly average volume concentrations were calculated for months with >50% daily data coverage. Volume concentrations of submicrometer aerosols were high in spring to early summer and low in winter. Significant increasing trends at 95% confidence levels were found for volume concentrations in winter–spring. Simulated monthly anthropogenic aerosol concentrations at Mt. Tateyama from results of regional aerosol modeling with emission inventory up to 2005 showed seasonal variation and winter–spring increasing trends similar to those of observed aerosol concentration. According to the model analyses, the contribution of anthropogenic aerosol concentrations derived from China was high during winter–spring (60–80% of total anthropogenic aerosols at Mt. Tateyama). This accords with the increasing trend observed for winter–spring. Because SO42− is the dominant component of total anthropogenic aerosols, these results suggest that increasing anthropogenic emissions, especially for SO2, in China, engender enhancement of submicrometer-diameter aerosols over Japan during winter–spring.

We investigated the influence of meteorological variability on the interannual variation of springtime boundary layer ozone over Japan during 1981–2005 by multiyear simulations with the Models-3 Community Multiscale Air Quality (CMAQ) modeling system and the Regional Emission Inventory in Asia (REAS). CMAQ/REAS generally reproduced the observed interannual variability of springtime ozone over Japan, showing year-to-year variations larger than the annual rate of increase of the long-term trend. We then analyzed the influence of the interannual variation of meteorology in simulated results by using the fixed emissions for 2000 and meteorological fields for each year. As a reference parameter, we calculated the area-weighted surface pressure anomaly over the Pacific Ocean east of Japan. When the anomaly has a large negative value, polluted air masses from continental Asia tend to be transported directly to Japan by westerly winds. In contrast, when the anomaly has a large positive value, influence of the outflow from continental Asia tends to be small because the westerly components of wind fields around Japan are comparatively weak. Instead, southerly winds are relatively strong and transport clean air masses from the Pacific Ocean to Japan. Consequently, springtime ozone over Japan is higher (lower) than in ordinary years when the anomaly has a large negative (positive) value. In general, the interannual variation of springtime ozone over Japan is sensitive to the outflow from continental Asia. We also found some correlation between springtime ozone over Japan and the El Niño-Southern Oscillation, indicating that higher and lower springtime ozone over Japan are related to La Niña and El Niño, respectively. Differences in the meridional displacement and diversity of cyclone tracks near Japan between El Niño and La Niña years may be responsible for interannual variations in the springtime boundary layer ozone over Japan.

Mineral dust is usually transported long distances in the lower troposphere. There are examples of Asian dust being transported across the Pacific Ocean 1‐7 , and traces of Asian dust have also been found in ice and snow cores in Greenland 8 and the French Alps 9 . Here, we use measurements from the Cloud‐Aerosol Lidar with Orthogonal Polarization 10 , an air parcel trajectory model and a three-dimensional aerosol transport model to map the transport of dust clouds generated during a storm in China’s Taklimakan Desert during May 2007. We show that the dust-veiled clouds were lofted to the upper troposphere around 8‐10 km above the Earth’s surface and transported more than one full circuit around the globe in about 13 days. When the dust reached the northwestern Pacific Ocean for the second time, the subsidence of a large-scale high-pressure system caused it to descend into the lower troposphere; some of the dust was then deposited over the ocean. Our analysis also indicates that the dust particles may have acted as ice nuclei in these high-altitude clouds, leading to the formation of cirrus clouds. We suggest that Asian dust can influence the global radiation budget by stimulating cirrus cloud formation and marine ecosystems by supplying nutrients to the open ocean. The polarization-sensitive Mie lidar is a powerful tool for the measurement of dust aerosols 11 . The first long-duration space-borne lidar optimized solely for atmospheric measurements (CloudAerosol

The effects of atmospheric nitrogen input on biological production in the Japan Sea have been investigated using a coupled physical-ecosystem model. Comparison between the cases with and without nitrogen deposition shows a relatively large effect on primary production in the southern Japan Sea during summer to autumn, when nitrogen deposition is high and nutrient is depleted in the surface layer. The atmospheric nitrogen deposition supports > 10% of the annual export production in the nearshore region along the Japanese coast. The importance of atmospheric input as a new nutrient will grow steadily with increasing deposition into the Japan Sea.

Three-dimensional structures of Asian dust transport in the planetary boundary layer (PBL) and free atmosphere occurring successively during the end of May 2007 were clarified using results of space-borne backscatter lidar, Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), and results simulated using a data-assimilated version of a dust transport model (RC4) based on a ground-based NIES lidar network. Assimilated results mitigated overestimation of dust concentration by reducing 17.4% of dust emissions and improved the root mean square difference (RMSD) of dust AOT between the model and NIES lidar by 31.2–66.9%. The dust layer depths, vertical and horizontal structure simulated by RC4 agreed with CALIOP from the dust source region to a long-range downwind region for which 3-D distribution of dust clouds had not been clarified previously. Based on CALIOP and RC4, two significant transport mechanisms of Asian dust in the PBL and free atmosphere were clarified: a low level dust outbreak within the dry slot region of a well developed low-pressure system, and formation of an elevated dust layer within the warm sector of a low-pressure system. Finally, the aging of pure dust particles was investigated using the particle depolarization ratio (PDR) at 532 nm and the color ratio (CR) at 1064 nm and 532 nm for the low-altitude dust transport case. Aerosols with high PDR were observed uniformly over the dust source region. As the dust cloud was transported to the eastern downwind regions, aerosols with low PDR and high CR were found in the layer of less than 1 km height, suggesting changes from the external to internal mixing state of spherical aerosols and dust in the surface layer.

The impact of the East Asia monsoon on the seasonal behavior of O3 in the boundary layer of Eastern China and the west Pacific region was analyzed for 2004–2006 by means of full-year nested chemical transport model simulations and continuous observational data obtained from three inland mountain sites in central and eastern China and three oceanic sites in the west Pacific region. The basic common features of O3 seasonal behaviors over all the monitoring sites are the pre- and post-monsoon peaks with a summer trough. Such bimodal seasonal patterns of O3 are predominant over the region with strong summer monsoon penetration, and become weaker or even disappear outside the monsoon region. The seasonal/geographical distribution of the pre-defined monsoon index indicated that the East Asia summer monsoon is responsible for the bimodal seasonal O3 pattern, and also partly account for the differences in the O3 seasonal variations between the inland mountain and oceanic sites. Over the inland mountain sites, the O3 concentration increased gradually from the beginning of the year, reached a maximum in June, decreased rapidly to the summer valley in July or August, and then peaked in September or October, thereafter decreased gradually again. Over the oceanic sites, O3 abundance showed a similar increasing trend beginning in January, but then decreased gradually from the end of March, followed by a wide trough with the minimum in July and August and a small peak in October or November. A sensitivity analysis performed by setting China-emission to zero revealed that the chemically produced O3 from China-emission contributed substantially to the O3 abundance, particularly the pre- and post-monsoon O3 peaks, over China mainland. We found that China-emission contributed more than 40% to total boundary layer O3 during summertime (60–70% in July) and accounted for about 40 ppb of each peak value over the inland region if without considering the effect of the nonlinear chemical productions. In contrast, over the oceanic region in the high monsoon index zone, the contribution of China-emission to total boundary layer O3 was always less than 20% (

Using an analysis of the first full year of CALIPSO lidar measurements, this paper derives unprecedented, altitude-resolved seasonal distributions of desert dust transported over the Tibetan Plateau (TP) and the surrounding areas. The CALIPSO lidar observations include numerous large dust plumes over the northern slope and eastern part of the TP, with the largest number of dust events occurring in the spring of 2007, and some layers being lofted to altitudes of 11–12 km. Generation of the Tibetan airborne dusts appears to be largely associated with source regions to the north and on the eastern part of the plateau. Examination of the CALIPSO time history reveals an "airborne dust corridor" due to the eastward transport of dusts originating primarily in these source areas. This corridor extends from west to east and shows a seasonality largely modulated by the TP through its dynamical and thermal forcing on the atmospheric flows. On the southern side, desert dust particles originate predominately in Northwest India and Pakistan. The dust transport occurs primarily in dry seasons around the TP western and southern slopes and dust particles become mixed with local polluted aerosols. No significant amount of dust appears to be transported over the Himalayas. Extensive forward trajectory simulations are also conducted to confirm the dust transport pattern from the nearby sources observed by the CALIPSO lidar. Comparisons with the OMI and MODIS measurements show the unique capability of the CALIPSO lidar to provide unambiguous, altitude-resolved dust measurements.

Simultaneous ground-based measurements of ozone (O3) and carbon monoxide (CO) were conducted in March 2005 as part of the East Asian Regional Experiment (EAREX) 2005 under the umbrella of the Atmospheric Brown Clouds (ABC) project. Multiple air quality monitoring networks were integrated by performing intercomparison of individual calibration standards and measurement techniques to ensure comparability of ambient measurements, along with providing consistently high time-resolution measurements of O3 and CO at the surface sites in East Asia. Ambient data collected from eight surface stations were compared with simulation results obtained by a regional chemistry transport model to infer recent changes in CO emissions from East Asia. Our inverse estimates of the CO emissions from China up to 2005 suggested an increase of 16% since 2001, in good agreement with the recent MOPITT satellite observations and the bottom-up estimates up to 2006. The O3 enhancement relative to CO in continental pollution plumes traversed in the boundary layer were examined as a function of transport time from the Asian continent to the western Pacific Ocean. The observed ΔO3/ΔCO ratios show increasing tendency during eastward transport events due likely to en-route photochemical O3 formation, suggesting that East Asia is an important O3 source region during spring.

We reviewed the data on the atmospheric SO2 and SO42− concentrations measured in a survey conducted by the Japan Environmental Laboratories Association (JELA). The data collected in the Tokai–Kinki–Hokuriku branch, which covers a 250-km×250-km region, were reviewed as one of the activities of the Tokai–Kinki–Hokuriku branch. The atmospheric SO2 and SO42− concentrations were measured using the four-stage filter-pack method. The data collected for 3 years (Campaign III by JELA) were reviewed. The SO2 concentration was affected by the eruption episode of the Miyakejima Volcano. In contrast, the SO42− concentration (annual mean in 1999: 35.0 nmol m−3) was scarcely affected by the eruption episode. The SO42− concentration level was within or slightly higher than the level of the European Monitoring Evaluation Program (EMEP) (lower than 30 nmol m−3) and that of mid-latitude North America. The particularity of the site would be potentially clarified by the relationship of the SO42−/(SO2+SO42−) ratio with the SO2 concentration and the correlation with the results of the Community Multi-scale Air Quality (CMAQ). The peculiar pattern of the monthly variation of the SO2 concentration clarified the particularity of the site, which was deeply associated to the spatial relationship with an express highway with heavy traffic and the wind rose.

Inverse modeling of Asian dust was performed using MODIS coarse-mode aerosol optical thickness (AOT) and a regional adjoint dust model. The a posteriori AOT shows better agreement with the MODIS AOT and OMI Aerosol index (AI). Independent validation with the NIES Lidar network shows that the inversion leads to a significant improvement and reduces root mean squares of differences by 29-32% at Seoul, Matsue, and Toyama. The inversion results show considerably greater dust emissions over the Gobi Desert and Mongolia. Especially, optimized emissions are estimated as 8.1 Tg (352% of the a priori) for 29 March and 19.5 Tg (325%) for 30 March. Comparison with inversion results using NIES Lidar (Yumimoto et al. 2008) shows consistency with our a posteriori dust emissions which underscores the feasibility of dust inversion with satellite optical observations, and encourages combined inversion that assimilates the Lidar extinction coefficient (vertical profiles) and MODIS AOT (horizontal distribution) concurrently. However, the a posteriori results might reflect effects of air pollutants from highly industrialized regions, which might contaminate the assimilated results. Further quality control of the input for the data assimilation is necessary in future studies.

A numerical analysis using a regional chemical transport model (CTM) is presented in comparison with Global Ozone Monitoring Experiment (GOME) and SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) satellite NO 2 measurements over East Asia from 1996 to 2005 from a climatological perspective. Modeling results agree well with satellite retrievals in geographical distribution patterns, with systematic underestimation of the absolute values. The sharp increase in NO 2 vertical column densities (VCDs) over central east China (CEC) after the year 2000 (14.1–20.5% yr −1 for the satellite observations and 10.8% yr −1 for model simulations) is analyzed quantitatively over different megacity clusters. The distinct emission increase patterns are responsible for the different increase trends observed over the Beijing megacity cluster (BJ), the Yangtze Delta (YD) and other CEC regions. The growth rate of satellite measured and CMAQ-modeled NO 2 VCDs for the YD is much higher than that in other regions, with no clear seasonal variation. Apart from BJ and YD, NO 2 emissions from other regions in CEC also expand considerably.

We studied trends in Asian air pollution in recent decades using air-quality monitoring station data, satellite retrieval data (GOME NO2), and regional-scale chemical transport model (CTM) simulation. A newly developed annual Asian-scale emission inventory (REAS) from 1980-2003 was used in observation data analysis and CTM. Analyses of recent trends in annual emissions in China by REAS and satellite GOME NO2 show an 8-10% increase after 2000 suggesting the impact of long-range transport of secondary air pollutants in regions and countries downwind. Detailed analyses of O3 observation data in Japan suggest an annual averaged O3 concentration increase of 2% yr-1 due to this long-range transport. We extended our regional air quality study targeting 2020. REAS provides three emission scenarios for China: the reference case (REF), the policy success case (PSC), and the policy failure case (PFC). Projected REF emissions for 2020 show O3 concentrations rising to 75 to 90 ppbv in June and 75 to 85 ppbv in August over the North China Plain. Projected PFC emissions bring an increase of monthly averaged O3 with greater than 20 ppbv (1 ppbv yr-1 growth) in the North China Plain. Surface O3 under the PFC scenario is enhanced by 6 to 8 ppbv over the Korean Peninsula and by 2 to 6 ppbv in Japan from 2000 to 2020 despite the reduction of NOx in Japan. This may become a critical level in air quality in Asia.

The relationship between long-term variation of Asian dust and climate indices was studied using a regional scale dust-transport model. Simulation results were examined using visibility-based observations by Chinese and Japanese Meteorological Agencies. Those results showed that the model reasonably captured interannual variations of Asian dust during 1972–2004. The long-term trend of dust days in the Gobi desert region showed a remarkable declining trend from the early 1980s–1997; the increasing trend of recent years (2000–02) was more conspicuous in Japan. Analyses of time variation of meteorological parameters in the Gobi region showed that the decreasing trend of dust days in this region is explained by the decreased frequency of strong winds. Additionally, anomaly analyses for dust and meteorological parameters in the Gobi region indicated that invasion of polar cold air played an important role in increasing dust phenomena. To clarify climate factors that affect dust emission and transport, regional climate indices that are appropriate for the scale of Asian dust storms were newly introduced. Correlation analyses between climate indices and simulated dust emissions showed that the dominant climate indices, which are closely correlated with dust emissions, were different in March and April. In March, the climate indices related to divergence of cold air from the polar region to mid-latitudes displayed a strong correlation with dust emissions, but during April, the climate index related to the south-north pressure gradient over the Gobi region exhibited a strong correlation with dust emission. Analyses of correlation between simulated surface dust concentrations and the Southern Oscillation Index (SOI) suggest that the El Nino/Southern Oscillation (ENSO) affects the dust transport path. Analyses of average dust transport flux at 130°E clarified variation of the transport path between La Nina years and El Nino years.

We developed a four-dimensional variational (4DVAR) data assimilation system for a regional chemical transport model (CTM). In this study, we applied it to inverse modeling of CO emissions in the eastern Asia during April 2001 and demonstrated the feasibility of our assimilation system. Three ground-based observations were used for data assimilation. Assimilated results showed better agreement with observations; they reduced the RMS difference by 16–27%. Observations obtained on board the R/V Ronald H. Brown were used for independent validation of the assimilated results. The CO emissions over industrialized east central China between Shanghai and Beijing were increased markedly by the assimilation. The results show that the annual anthropogenic (fossil and biofuel combustion) CO emissions over China are 147 Tg. Sensitivity analyses using the adjoint model indicate that the high CO concentration measured on 17 April at Rishiri, Japan (which the assimilation was unable to reproduce) originated in Russia or had traveled from outside the Asian region (e.g. Europe).

The Models-3 Community Multi-scale Air Quality (CMAQ) modeling system with meteorological fields calculated by the Regional Atmospheric Modeling System (RAMS) was applied to East Asia to investigate the transport and photochemical transformation of tropospheric ozone during the Transport and Chemical Evolution over the Pacific (TRACE-P) field campaign. Modeled concentrations of hydroxyl radical, hydroperoxyl radical, nitric oxide, nitrogen dioxide, ethene, ethane, carbon monoxide, and ozone were compared with observations obtained onboard of two aircrafts in order to evaluate the model performance. Comparison indicates that the model reproduced the tempo-spatial distributions of ozone and its related chemical species reasonably well, and most model results were within a factor of 2 of the observations.

The Models-3 Community Multi-scale Air Quality modeling system (CMAQ) coupled with the Regional Atmospheric Modeling System (RAMS) is used to simulate three-dimensional concentration distributions of hydroxyl (OH) and hydroperoxyl (HO2) radicals over the western Pacific Ocean during the NASA Transport and Chemical Evolution over the Pacific (TRACE-P) field campaign. Modeled values of OH and HO2 and their closely related chemical species and photolysis rates are compared with observational data collected onboard the DC-8 aircraft. Comparison shows that the model reasonably reproduced these observed values over a broad range of conditions with an overall tendency to overestimate the measured OH and HO2 by a factor of 1.56 and 1.24, respectively. A case study of OH, HO2 and their closely related chemical species and photolysis rates along the DC-8 flights 11 and 12 conducted on 17–18 March 2001 shows that the model reproduces the temporal and spatial variations reasonable well, and produces more reliable OH and HO2 concentrations in the polluted environment than in the clean marine boundary layer.

ACE-Asia was a multi-national collaboration organized to investigate and understand the chemistry, radiative properties, and climatic effects of mineral dust and other aerosol particles in the East Asia/Northwest Pacific region. Studies conducted at the Gosan and Zhenbeitai surface supersites show striking variations in aerosol concentrations and properties that were affected by the occurrence and origins of the Asian dust storms, air mass pathways, and mixing during the transport. Investigations conducted on the R/V Ronald H. Brown (RHB) showed that dust had a pervasive influence on the chemical composition, size distribution, and optical properties of the aerosol. Analyses using an aerosol time-of-flight mass spectrometer on the RHB showed that most of the coarse-particle nitrate and sulfate in post-frontal air was associated with dust, and more remarkably, that competitive or exclusionary processes evidently are involved in the uptake or production of these substances. Studies conducted onboard the NCAR C-130 aircraft showed that coarse-mode dust was less absorbing and less hygroscopic than pollution aerosol and that there was little correlation in light scattering and absorption by the sub- vs. super-micrometer aerosol. Below ∼2 km, dust was commonly mixed with pollutants, and this had a stronger influence on the optical properties of the submicrometer particles than the coarse-mode dust; at higher altitudes, the dust was less affected by pollution. Single particle analyses of C-130 samples showed that the mixing of black carbon (BC) with dust was common, but only certain types of BC particles were aggregated. Models were used in the planning, execution and interpretative phases of ACE-Asia; and summaries of modeling results are presented to illustrate the progress being made in identifying new dust sources; in depicting the time-varying, three-dimensional structure of dust plumes; and in quantifying the production, transport, and deposition of Asian dust.

An intensive field survey, with 6-h measurement intervals, of concentrations of chemical species in particulate matter and gaseous compounds was carried out at coastal sites on the Sea of Japan during winter. The concentration variation of SO2(g) and HNO3(g) were well correlated, whereas the NH3(g) concentration variation had no correlation with those of SO2(g) and HNO3(g). The NH4 + (p)/non-sea-salt- (nss-)SO4 2 −(p) ratio in particulate matter was mainly affected by the location of the sampling site. One or more concentration peaks of nss-Ca2 + for survey period were observed. Backward trajectories analyses for the highest nss-Ca2 + concentration peaks showed some inconsistency in pathways. We consider that insufficient mixing of the atmosphere and/or insufficient time for the transported air pollutants to react with those discharged locally are the most likely explanations for the discrepancies between the measured products [HNO3][NH3] and the calculated values.

Ozone (O 3 ) concentrations in East Asia were simulated using the Community Multi-scale Air Quality model and their reproducibility was confirmed by comparing with observation data at Japanese monitoring sites. The model can reproduce the seasonal variation of surface O 3 over Japan. In particular, for the southern parts of Japan, simulated surface O 3 concentrations are strongly correlated with observations. Surface O 3 distribution over East Asia varies dynamically from season to season according to the meteorological condition. In May and June, 2-month average O 3 concentrations in the boundary layer are highest, 55–70 ppbv over East China and Japan at 35–40°N. We estimated the seasonal variation of the contribution of chemically produced O 3 by east Asian regional emissions. In the summertime, the contribution of the regional Asian emissions to O 3 concentrations is around 40–70% over most of China, and the highest is 60–70% ( 3 concentrations over East Asia are strongly influenced by the chemical production by regional emissions during summer season. However, the inflow from outside of this model domain also contributes substantial O 3 concentration over East Asia and its contribution is predominant in winter and early spring. The seasonal change of O 3 concentrations over Japan is characterized by two peaks in spring and autumn and summer minimum. The spring peak event in 2002 consists of split peaks: the first peak in Mar–Apr is mainly influenced by the inflow from outside of this model domain, the second spring peak between May and June is mainly influenced by chemically produced O 3 by regional emissions. During the summer season, O 3 concentrations are the lowest over year because of the weak Asian outflow and northward penetration of the marine air mass.

The Aeolian Dust Experiment on Climate Impact (ADEC) was initiated in April 2000 as a joint five-year Japan–China project. The goal was to understand the impact of aeolian dust on climate via radiative forcing (RF). Field experiments and numerical simulations were conducted from the source regions in northwestern China to the downwind region in Japan in order to understand wind erosion processes temporal and spatial distribution of dust during their long-range transportation chemical, physical, and optical properties of dust and the direct effect of radiative forcing due to dust. For this, three intensive observation periods (IOP) were conducted from April 2002 to April 2004. The in situ and network observation results are summarized as follows: (1) In situ observations of the wind erosion process revealed that the vertical profile of moving sand has a clear size dependency with height and saltation flux and that threshold wind velocity is dependent on soil moisture. Results also demonstrated that saltation flux is strongly dependent on the parent soil size distribution of the desert surface. (2) Both lidar observations and model simulations revealed a multiple dust layer in East Asia. A numerical simulation of a chemical transport model, CFORS, illustrated the elevated dust layer from the Taklimakan Desert and the lower dust layer from the Gobi Desert. The global-scale dust model, MASINGAR, also simulated the dust layer in the middle to upper free troposphere in East Asia, which originated from North Africa and the Middle East during a dust storm in March 2003. Raman lidar observations at Tsukuba, Japan, found the ice cloud associated with the dust layer at an altitude of 6 to 9 km. Analysis from lidar and the radio-sonde observation suggested that the Asian dust acted as ice nuclei at the ice-saturated region. These results suggest the importance of dust's climate impact via the indirect effect of radiative forcing due to the activation of dust into ice nuclei. (3) Studies on the aerosol concentration indicated that size distributions of aerosols in downwind regions have bimodal peaks. One peak was in the submicron range and the other in the supermicron range. The main soluble components of the supermicron peak were Na+, Ca2+, NO3−, and Cl−. In the downwind region in Japan, the dust, sea salt, and a mixture of the two were found to be dominant in coarse particles in the mixed boundary layer. (4) Observation of the optical properties of dust by sky-radiometer, particle shoot absorption photometer (PSAP), and Nephelometer indicated that unpolluted dust at source region has a weaker absorption than originally believed. A sensitivity experiment of direct RF by dust indicated that single scattering albedo is the most important of the optical properties of dust and that the sensitivity of instantaneous RF in the shortwave region at the top of the atmosphere to the refractive index strongly depends on surface albedo. A global scale dust model, MASINGAR, was used for evaluation of direct RF due to dust. The results indicated the global mean RF at the top and the bottom of the atmosphere were − 0.46 and − 2.13 W m− 2 with cloud and were almost half of the RF with cloud-free condition.

We assessed the spectral imaginary part of refractive index (n i) of Asian dust aerosol in the visible wavelengths (0.412-0.865 µm) by comparing simulated and satellite-observed top of the atmosphere (TOA) reflectances. The approach employed in this study combines the results obtained from SeaWiFS ocean color sensor, the vertical profiles provided by CFORS mesoscale transport model, and the size distribution observed concurrently by Aerosol Robotic Network (AERONET) sites. Analyses for four dust instances over the Sea of Japan during 2001 and 2002 showed that the n i values of Asian dust are significantly lower than previously published, as low as about 0.001 at 0.5 µm. Although the backward trajectories suggest that the four events have different sources, all events show very similar n i values. The corresponding averaged coarse-mode dust single-scattering albedo (SSA) is found to be 0.98 ± 0.002 at 0.555 µm, which is consistent with the results of several contemporaneous observations conducted during Asian Aerosol Characterization Experiment (ACE-Asia). These results indicate that Asian dust particles itself may cool the climate system more strongly than is generally considered and a weakly absorbing model of Asian dust is more appropriate for use in climate modeling than the already used dust model.

We have conducted dust observations at a number of locations including Beijing, Hefei, Suwon, Fukue, Nagasaki, Tsukuba, and Sapporo using automated two-wavelength polarization lidars o study Asian dust phenomena, including generation, transport, and change during transport. We developed a method using the depolarization ratio for estimating the contributions of Asian dust and spherical air-pollution aerosols in observed aerosol mixtures. We analyzed the dust profiles statistically to derive climatological characteristics and year-on-year variations. We also studied dust source and transport path for each dust event using the regional chemical transport model CFORS. The statistical analysis clearly demonstrated the year-on-year variation of dust phenomena and the characteristics depending on the locations of the observational sites. Most major dust events in 2001 and 2002 originated in Inner Mongolia and/or Mongolia at the southern edge of a low-pressure area located in Siberia and were transported by strong westerlies. In 2003, the typical meteorological pattern for heavy dust cases accompanying a strong low in Siberia was not seen, except for one case in April. Furthermore, the lidar observation in Beijing suggests that less dust was generated in the source regions in Inner Mongolia and/or Mongolia, probably due to higher precipitation in 2003.

A 1-year record of hourly atmospheric radon-222 concentration observations at three ACE-Asia network sites—Hok Tsui (Hong Kong), Gosan (Jeju Island) and Mauna Loa Observatory (Hawaii)—is presented and discussed. The observations include the spring 2001 ACE-Asia intensive operation period. Site locations were chosen for the experimental characterization of both boundary layer (Hok Tsui, Gosan) and free tropospheric (Mauna Loa) continental outflow to the Pacific. A significant seasonal variability in background radon concentration is quantified at each site with the ratios of winter maximum to summer minimum background of 96, 15 and 3 for Hok Tsui, Gosan and Mauna Loa, respectively. Only during summer were background radon concentrations directly comparable with unperturbed marine values (∼20 mBq m −3 ). The variability in radon signal was characterized at each site on diurnal to seasonal timescales. The seasonal variability in fetch regions for air masses experiencing the greatest and smallest terrestrial influence was characterized using 10-day back trajectories of air masses corresponding to radon concentrations higher (lower) than the 90th (10th) percentile value. The trajectory analyses for Hok Tsui and Gosan, as well as a direct analysis of the experimental results, further supports the previously postulated existence of a strong spatial heterogeneity in the radon source strength in East Asia. Back trajectories of free tropospheric air masses reaching Mauna Loa indicated source regions deep within the Asian continent primarily between 20 and 40°N. This fetch region is different from that influencing the Hok Tsui and Gosan sites. The radon concentration of air masses reaching Mauna Loa was shown to vary seasonally as well as with latitude of the predominant fetch region. Possible mechanisms of this phenomenon have been identified and include (a) seasonal variation in the radon source, (b) seasonal variation in the strength, frequency and/or efficiency of mechanisms that lift boundary layer air to the mid troposphere and (c) seasonal variation in the latitudinal axis of convection. DOI: 10.1111/j.1600-0889.2005.00133.x

A nested regional meteorology/dust-transport model was applied to an Asian region including the Taklimakan Desert. A three-grid system with a resolution of 81 km, 27 km and 9 km was designed and model calculation was conducted over the whole period of Apri1 2001 to examine the typical springtime meteorology and some dust episodes over the Taklimakan Desert region. The performance model was examined based on meteorological observation at WMO SYNOP station surrounding the Taklimakan Desert and ADEC special observation site at Qira. The model results reproduced complicated airflows within the Tarim Basin, strong down slope winds from the Tianshan Mountains when meteorological disturbances crosses over the Taklimakan region, and a strong easterly flow from the Hexi Corridor side. Composite analysis when the Tazhong site simulated an easterly wind was conducted and showed that the percentage of the occurrence of this condition was approximately 50% of the full simulation period. The scale of the easterly wind zone is 400 km in the Y direction, 1000 km in the X direction and 2-3 km vertically. Simulated high dust concentration shows a good correlation with this easterly wind zone. The model’s averaged dust concentration fields showed that the surface concentration ratio was approximately 0.6 between the eastern and western side of the Tarim Basin. However, the modeled ratio showed an opposite relation with the SYNOP visibility, thereby indicating that the current high wind type dust emission scheme may be insuflicient to simulate the suspended dust phenomena in the western part of the Tarim Basin.

Dust layers in the free troposphere were observed with the lidars in Suwon, Gosan, and Tsukuba in March 7-9, 2005. The observed dust distributions were compared with the results of the regional and global dust transport models (CFORS, NRL NAAPS, and SPRINTARS). The results with the global models reproduced the dust layer qualitatively, but the regional model did not. This suggests the source of the dust layers is located outside of the modeled region of the regional model that includes Taklimakan Desert and Gobi Desert. The global models showed the plumes were from the Sahara Desert, and the both models showed there was no major dust emission in Taklimakan and Gobi Deserts during the observation period. The trajectory analysis using NOAA HYSPLIT showed that the dust originated in the Sahara Desert 5-10 days before.