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In this study, we developed a data assimilation (DA) system for chemical transport model (CTM) simulations using an ensemble Kalman filter (EnKF) technique. This DA technique is easy to implement in an existing system without seriously modifying the original CTM and can provide flow-dependent corrections based on error covariance by short-term ensemble propagations. First, the PM 2.5 observations at ground stations were assimilated in this DA system every 6 h over South Korea for the period of the KORUS–AQ campaign from 1 May to 12 June 2016. The DA performances with the EnKF were then compared to a control run (CTR) without DA and a run with three-dimensional variational (3D-Var) DA. Consistent improvements owing to the initial conditions (ICs) assimilated with the EnKF were found in the DA experiments at a 6 h interval compared to the CTR run and to the run with 3D-Var. In addition, we attempted to assimilate the ground observations from China to examine the impacts of improved boundary conditions (BCs) on the PM 2.5 predictability over South Korea. The contributions of the ICs and BCs to improvements in the PM 2.5 predictability were also quantified. For example, the relative reductions in terms of the normalized mean bias (NMB) were found to be approximately 27.2 % for the 6 h reanalysis run. A series of 24 h PM 2.5 predictions were additionally conducted each day at 00:00 UTC with the optimized ICs. The relative reduction of the NMB was 17.3 % for the 24 h prediction run when the updated ICs were applied at 00:00 UTC. This means that after the application of the updated BCs, an additional 9.0 % reduction in the NMB was achieved for 24 h PM 2.5 predictions in South Korea. [ABSTRACT FROM AUTHOR]

In this study, we developed a data assimilation (DA) system for chemical transport model (CTM) simulations using an ensemble Kalman filter (EnKF) technique. This DA technique is easy to implement to an existing system without seriously modifying the original CTM, and can provide flow-dependent corrections based on error covariance by short-term ensemble propagations. First, the PM2.5 observations at ground stations were assimilated in this DA system every 6 hours over South Korea for the period of the KORUS-AQ campaign, from 1 May to 12 June, 2016. The DA performances with the EnKF were then compared to a control run (CTR) without DA, as well as a run with three-dimensional variational (3DVAR) DA. Consistent improvements due to the ICs assimilated with the EnKF were found in the DA experiments with 6 h interval, compared to the CTR run, and to the run with 3DVAR. In addition, we attempted to assimilate the ground observations from China to examine the impacts of improved boundary concentrations (BCs) on the PM2.5 predictability over South Korea. The contributions of the ICs and BCs to improvements in the PM2.5 predictability were also quantified. For example, the relative reductions in terms of the normalized mean bias (NMB) were found to be about 27.2 % for the 6 h reanalysis run. A series of 24 hour PM2.5 predictions were additionally conducted each day at 00 UTC with the optimized initial concentrations (ICs). The relative reduction of the NMB was 17.3 % for the 24 h prediction run, when the updated ICs were applied at 00 UTC. This means that after the application of the updated BCs, an additional 9.0 % reduction in the NMB was achieved for 24 h PM2.5 predictions in South Korea. [ABSTRACT FROM AUTHOR]

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 PM 2.5 and PM 10 concentrations, as well as the nitrate and sulfate concentrations in fine (aerodynamic diameter ≤ 2.5 μm) and coarse mode (2.5 μm < aerodynamic diameter ≤ 10 μm). This episode originated from two dust events that occurred in the inland desert areas of Mongolia and China, and then the long-range transported dust and anthropogenic pollutants were trapped over the downwind region of East Asia for more than one week due to the blocked north Pacific subtropical high-pressure system over the east of Japan. The model results showed that mineral dust accounted for 53–83% of PM 10 , and 39–67% of PM 2.5 over five cities in East Asia during this episode. Sensitivity analysis indicated that the Qingdao and Seoul regions experienced dust and pollution twice, by direct transport from the dust source region and from dust detoured over the Shanghai area. The results of the NAQPMS model confirmed the importance of dust heterogeneous reactions (HRs) over East Asia. Simulated dust NO 3 − concentrations accounted for 75% and 84% of total NO 3 − in fine and coarse mode, respectively, in Fukuoka, Japan. The horizontal distribution of model results revealed that the ratio of dust NO 3 − /dust concentration increased from about 1% over the Chinese land mass to a maximum of 8% and 6% respectively in fine and coarse mode over the ocean to the southeast of Japan, indicating that dust NO 3 − was mainly formed over the Yellow Sea and the East China Sea before reaching Japan. [ABSTRACT FROM AUTHOR]

Appropriate policies to improve air quality by reducing anthropogenic emissions are urgently needed. This is typified by the particulate matter (PM) problem and it is well known that one type of PM, sulfate aerosol (SO 4 2− ), has a large-scale impact due to long range transport. In this study we evaluate the source–receptor relationships of SO 4 2− over East Asia for 2005, when anthropogenic sulfur dioxide (SO 2 ) emissions from China peaked. SO 2 emissions from China have been declining since 2005–2006, so the possible maximum impact of Chinese contributions of SO 4 2− is evaluated. This kind of information provides a foundation for policy making and the estimation of control effects. The tagged tracer method was applied to estimate the source apportionment of SO 4 2− for 31 Chinese province-scale regions. In addition, overall one-year source apportionments were evaluated to clarify the seasonal dependency. Model performance was confirmed by comparing with ground-based observations over mainland China, Taiwan, Korea, and Japan, and the model results fully satisfied the performance goal for PM. We found the following results. Shandong and Hebei provinces, which were the largest and second largest SO 2 sources in China, had the greatest impact over the whole of East Asia with apportionments of around 10–30% locally and around 5–15% in downwind receptor regions during the year. Despite large SO 2 emissions, the impact of south China (e.g., Guizhou, Guangdong, and Sichuan provinces) was limited to local impact. These results suggest that the reduction policy in south China contributes to improving the local air quality, whereas policies in north and central China are beneficial for both the whole of China and downwind regions. Over Taiwan, Korea, and Japan, the impact of China was dominant; however, local contributions were important during summer. [ABSTRACT FROM AUTHOR]

To improve the predictability of concentrations of atmospheric particulate matter, a data assimilation (DA) system using ensemble square root filter (EnSRF) has been developed for the Community Multiscale Air Quality (CMAQ) model. The EnSRF DA method is a deterministic variant of the ensemble Kalman filter (EnKF) method, which means that unlike the EnKF method, it does not add random noise to the observations. To compare the performances of the EnSRF with those of other DA methods, such as EnKF and 3DVAR (three-dimensional variational), these three methods were applied to the same CMAQ model simulations with identical experimental settings. This is the first attempt in the field of chemical DA to compare the EnKF and EnSRF methods. An identical set of surface fine particulate matter (PM 2.5) were assimilated every 6 h by all the DA methods over a CMAQ domain of East Asia, during the period from 01 May to 11 June 2016. In parallel with 'reanalysis experiments', we also carried out '48 h prediction experiments' using the optimized initial conditions produced by the three DA methods. Detailed analyses among the three DA methods were then carried out by comparing both the reanalysis and the prediction outputs with the observed surface PM 2.5 over four regions (i.e., South Korea, the Beijing–Tianjin–Hebei (BTH) region, Shandong province, and Liaoning province). The comparison results revealed that the EnSRF produced the best reanalysis and prediction fields in terms of several statistical metrics. For example, when the 3DVAR, EnKF, and EnSRF methods were used, averaged normalized mean biases (NMBs) decreased by (57.6, 85.6, and 91.8) % in reanalyses and (39.7, 87.6, and 91.5) % in first-day predictions, compared to the CMAQ control experiment (i.e., without DA) over South Korea, respectively. Also, over the three Chinese regions, the EnSRF method outperformed the EnKF and 3DVAR methods. [Display omitted] • The EnSRF method produced the best reanalysis and prediction fields for PM 2.5. • The impacts of the EnSRF method remained throughout the 48 h of prediction range. • The EnSRF-CMAQ DA system can be applied in the operational aerosol forecasting in future. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: To illuminate the issue of trans-boundary O3 pollution and regional O3 reduction policies in East Asia, we have investigated the East Asian ozone (O3) response to perturbations caused by Chinese anthropogenic emissions using the Community Multiscale Air Quality (CMAQ) model, a regional chemical transport model. The O3 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 O3 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 O3 formation in a model experiment to investigate East Asian scale O3 source-receptor relationships. On the other hand, the O3 response is strongly nonlinear in April at Hong Kong, where the current NMVOCs/NOx ratio is low and the O3 production regime is easily moved to the NMVOCs sensitive region. The O3 responses to the NOx emission changes have been investigated using surface O3 concentrations at remote Japanese sites and tropospheric NO2 vertical column density (NO2 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 NO2 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 O3 concentration in the downwind region during 2003–2009 responds linearly to a change of the NO2 VCD over central east China both in the model and in the observation. The corresponding O3 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 NO2 VCD from 2004, leads to O3 increments of 5ppbv and 8ppbv in the model and in the observation, respectively. The modeled O3 increase due to changes in NOx emission explains approximately 60% of the observed O3 trend at remote Japanese sites. Thus, approximately 40% of the observed O3 increase is unaccounted for by the NOx emissions growth. [Copyright &y& Elsevier]

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 SO2 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 SO2 emissions from China produce significant quantities of summertime sulfate aerosols downwind of source areas. We used a parametric scaling method for estimating anthropogenic SO2 emissions in China. Using column amounts of SO2 derived from satellite data, and relationships between the column amounts of SO2 and anthropogenic emissions, 2009 emissions were diagnosed. The results showed that 2009 emissions of SO2 from China were equivalent to 2004 levels. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Dust aerosol has important climate and environmental effects, which could be changed by internally mixing with anthropogenic aerosol as a result of heterogeneous reactions; however, the importance of these reactions is not fully understood yet. In this study, synergetic observations and an air quality model were used to analyze the transport of a severe dust storm and its impacts on nitrate and sulfate levels over East Asia between 3 and 11 May 2017. The model successfully reproduced the occurrence and transport of the dust storm compared to dust RGB imageries of the Himawari-8 satellite and dust extinction coefficients observed by LIDAR. The model also reasonably simulated the variations of observed nitrate and sulfate concentrations, and the results indicated that the dust heterogeneous reactions were dominant pathways for nitrate formation, but they had limited contribution for sulfate in both fine and coarse mode in Fukuoka, Japan. Dust nitrate formed rapidly after leaving China, and the highest period-averaged concentration of dust nitrate (>5 μg m−3) was shown over the Yellow Sea. Based on model results; we found that the mass ratio of dust nitrate to dust aerosol could reach 10% over the Pacific Ocean. Our results confirmed the importance of heterogeneous reactions on compositions of dust particles. [ABSTRACT FROM AUTHOR]

The impact of heterogeneous reactions on the chemical components and mixing state of dust particles are investigated by observations and an air quality model over northern China between March 27, 2015 and April 2, 2015. Synergetic observations were conducted using a polarization optical particle counter (POPC), a depolarized two-wavelength Lidar and filter samples in Beijing. During this period, dust plume passed through Beijing on March 28, and flew back on March 29 because of synoptic weather changes. Mineral dust mixed with anthropogenic pollutants was simulated using the Nested Air Quality Prediction Modeling System (NAQPMS) to examine the role of heterogeneous processes on the dust. A comparison of observations shows that the NAQPMS successfully reproduces the time series of the vertical profile, particulate matter concentration, and chemical components of fine mode (diameter ≤ 2.5 μm) and coarse mode (2.5 μm < diameter ≤ 10 μm) particles. After considering the heterogeneous reactions, the simulated nitrate, ammonium, and sulfate are in better agreement with the observed values during this period. The modeling results with observations show that heterogeneous reactions are the major mechanisms producing nitrate reaching 19 μg/m 3 , and sulfate reaching 7 μg/m 3 , on coarse mode dust particles, which were almost 100% of the coarse mode nitrate and sulfate. The heterogeneous reactions are also important for fine mode secondary aerosols, for producing 17% of nitrate and 11% of sulfate on fine mode dust particles, with maximum mass concentrations of 6 μg/m 3 and 4 μg/m 3 . In contrast, due to uptake of acid gases (e.g. HNO 3 and SO 2 ) by dust particles, the fine mode anthropogenic ammonium nitrate and ammonium sulfate decreased. As a result, the total fine mode nitrate decreased with a maximum of 14 μg/m 3 , while the total fine mode sulfate increased with a maximum of 2 μg/m 3 . Because of heterogeneous reactions, 15% of fine mode secondary inorganic aerosols and the entire coarse mode nitrate and sulfate were internally mixed with dust particles. The significant alterations of the chemical composition and mixing state of particles due to heterogeneous reactions are important for the direct and indirect climate effects of dust and anthropogenic aerosols. [ABSTRACT FROM AUTHOR]

Abstract: Ozone (O3) 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 O3 over Japan. In particular, for the southern parts of Japan, simulated surface O3 concentrations are strongly correlated with observations. Surface O3 distribution over East Asia varies dynamically from season to season according to the meteorological condition. In May and June, 2-month average O3 concentrations in the boundary layer are highest, 55–70ppbv over East China and Japan at 35–40°N. We estimated the seasonal variation of the contribution of chemically produced O3 by east Asian regional emissions. In the summertime, the contribution of the regional Asian emissions to O3 concentrations is around 40–70% over most of China, and the highest is 60–70% (<35ppbv) at the mouth area of Yantze River. This suggests that O3 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 O3 concentration over East Asia and its contribution is predominant in winter and early spring. The seasonal change of O3 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 O3 by regional emissions. During the summer season, O3 concentrations are the lowest over year because of the weak Asian outflow and northward penetration of the marine air mass. [Copyright &y& Elsevier]

In this study, we developed a data assimilation (DA) system for chemical transport model (CTM) simulations using an ensemble Kalman filter (EnKF) technique. This DA technique is easy to implement to an existing system without seriously modifying the original CTM, and can provide flow-dependent corrections based on error covariance by short-term ensemble propagations. First, the PM2.5 observations at ground stations were assimilated in this DA system every 6 hours over South Korea for the period of the KORUS-AQ campaign, from 1 May to 12 June, 2016. The DA performances with the EnKF were then compared to a control run (CTR) without DA, as well as a run with three-dimensional variational (3DVAR) DA. Consistent improvements due to the ICs assimilated with the EnKF were found in the DA experiments with 6 h interval, compared to the CTR run, and to the run with 3DVAR. In addition, we attempted to assimilate the ground observations from China to examine the impacts of improved boundary concentrations (BCs) on the PM2.5 predictability over South Korea. The contributions of the ICs and BCs to improvements in the PM2.5 predictability were also quantified. For example, the relative reductions in terms of the normalized mean bias (NMB) were found to be about 27.2 % for the 6 h reanalysis run. A series of 24 hour PM2.5 predictions were additionally conducted each day at 00 UTC with the optimized initial concentrations (ICs). The relative reduction of the NMB was 17.3 % for the 24 h prediction run, when the updated ICs were applied at 00 UTC. This means that after the application of the updated BCs, an additional 9.0 % reduction in the NMB was achieved for 24 h PM2.5 predictions in South Korea. [ABSTRACT FROM AUTHOR]

We reviewed the data on the atmospheric SO2 and SO4 2− 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 SO4 2− 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 SO4 2− concentration (annual mean in 1999: 35.0nmolm−3) was scarcely affected by the eruption episode. The SO4 2− concentration level was within or slightly higher than the level of the European Monitoring Evaluation Program (EMEP) (lower than 30nmolm−3) and that of mid-latitude North America. The particularity of the site would be potentially clarified by the relationship of the SO4 2−/(SO2+SO4 2−) 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. [Copyright &y& Elsevier]

East Asia is suffering from both severe air pollution problem due to intensive anthropogenicemissions and natural mineral dust aerosols. During transport, the aerosol particles undergocomplex mixing processes, resulting in great impacts on regional air quality, human healthand climate. In this study, we conducted a long-term observation using an Optical ParticleCounter equipped with a Polarization detection module (POPC) at an urban sitein Beijing. Mass concentrations of both PM2.5 and PM10 estimated from POPCcompared well with ground-based measurements. The results revealed that theobserved depolarization ratio (DR, termed as the ratio of the intensity of the s-polarizedsignal to the intensity of the 120 degree backward scattering signal [s/(s + p)])for aerosol particles in the fine mode was generally much lower in summer thanthat in spring as a result of predominance of different aerosol types. Mineral dustparticles in the coarse mode normally had a large DR value (0.3 ± 0.05) owing to theirnon-spherical shape; however, particles in the fine mode consisted of large proportionwater-soluble compositions, which lead to apparent decrease of their DR values inparticular high relative humidity (RH) condition. Because the observation site wassubject to frequent impact of dust event in spring, DR value of particle at 1 μm wasalmost twice as high as that (0.07 ± 0.01) in summer. Based on size-resolved DRvalues, anthropogenic pollutants, mineral dust and polluted mineral dust particles,and their contribution to local air quality were well distinguished. About 26.7%of substandard days (daily averaged PM2.5 concentration larger than 75 μg/m3)in Beijing was featured by high atmospheric loading of coarse-mode particles inwinter-spring time. In particular during severe pollution episode in winter, the DRvalues of coarse mode particles decreased by 13%, implies the high possibility ofdust-related heterogeneous processes on pollution formation. During dust event, DRvalues of particle at Dp = 5 μm decreased evidently with increase of PM2.5/PM10ratio as well as RH, indicating of the morphological changes of mineral dust. Thisstudy confirmed that high RH tends to promote water absorption processes on thedust surface as well as coating of soluble compounds, and suggested that complexmixing of dust and anthropogenic particles may lead to underestimate impact ofdust particles in urban area based on remote sensing technique, and interactionbetween dust particle and pollutants should be well considered by the optical model. [ABSTRACT FROM AUTHOR]