Search

Occupational exposure to welding fumes constitutes a serious health concern. Although the effects of fumes on the respiratory tract have been investigated, few apparent reports were published on their effects on the skin. The purpose of this study was to investigate the effects of exposure to welding fumes on skin cells, focusing on interleukin-24 (IL-24), a cytokine involved in the pathophysiology of skin conditions, such as atopic dermatitis and psoriasis. Treatment with welding fumes increased IL-24 expression and production levels in human dermal microvascular endothelial cells (HDMEC) which were higher than that in normal human epidermal keratinocytes. IL-24 levels in Trolox and deferoxamine markedly suppressed welding fume-induced IL-24 expression in HDMEC, indicating that oxidative stress may be involved in this cytokine expression. IL-24 released from HDMEC protected keratinocytes from welding fume-induced damage and enhanced keratinocyte migration. Serum IL-24 was higher in welding workers than in general subjects and was positively correlated with elevated serum levels of 8-hydroxy-2'-deoxyguanosine, an oxidative stress marker. In summary, welding fumes enhanced IL-24 expression in HDMEC, stimulating keratinocyte survival and migration. IL-24 expression in endothelial cells may act as an adaptive response to welding-fume exposure in the skin. [ABSTRACT FROM AUTHOR]

Microplastic pollution is occurring in most ecosystem, yet their presence in high altitude clouds and their influence on cloud formation and climate change are poorly known. Here we analyzed microplastics in cloud water sampled at the summits of Japan mountains at 1300–3776 m altitude by attenuated total reflection imaging and micro-Fourier transform infrared spectroscopy. We observed nine microplastics including polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyamide 6, polycarbonate, ethylene–propylene copolymer or polyethylene–polypropylene alloy, polyurethane, and epoxy resin. Microplastic were fragmented, with mean concentrations ranging from 6.7 to 13.9 pieces per liter, and with Feret diameters ranging from 7.1 to 94.6 μm. Microplastics bearing hydrophilic groups such as carbonyl and/or hydroxyl groups were abundant, suggesting that they might have acted as condensation nuclei of cloud ice and water. Overall, our finding suggest that high-altitude microplastics cloud influence cloud formation and, in turn, might modify the climate. [ABSTRACT FROM AUTHOR]

Exposure to particulate matter less than 2.5 µm in diameter (PM2.5) is a cause of concern in cities and major emission regions of northern India. An intensive field campaign involving the states of Punjab, Haryana and Delhi national capital region (NCR) was conducted in 2022 using 29 Compact and Useful PM2.5 Instrument with Gas sensors (CUPI-Gs). Continuous observations show that the PM2.5 in the region increased gradually from < 60 µg m−3 in 6–10 October to up to 500 µg m−3 on 5–9 November, which subsequently decreased to about 100 µg m−3 in 20–30 November. Two distinct plumes of PM2.5 over 500 µg m−3 are tracked from crop residue burning in Punjab to Delhi NCR on 2–3 November and 10–11 November with delays of 1 and 3 days, respectively. Experimental campaign demonstrates the advantages of source region observations to link agricultural waste burning and air pollution at local to regional scales. [ABSTRACT FROM AUTHOR]

The impacts of renewable energy shifting, passenger car electrification, and lightweighting through 2050 on the atmospheric concentrations of PM2.5 total mass and oxidative stress‐inducing metals (PM2.5‐Fe, Cu, and Zn) in Japan were evaluated using a regional meteorology–chemistry model. The surface concentrations of PM2.5 total mass, Fe, Cu, and Zn in the urban area decreased by 8%, 13%, 18%, and 5%, respectively. Battery electric vehicles (BEVs) have been considered to have no advantage in terms of non‐exhaust PM emissions by previous studies. This is because the disadvantages (heavier weight increases tire wear, road wear, and resuspention) offset the advantages (regenerative braking system (RBS) reduces brake wear). However, the future lightweighting of drive battery and body frame were estimated to reduce all non‐exhaust PM. Passenger car electrification only reduced PM2.5 concentration by 2%. However, Fe and Cu concentrations were more reduced (−8% and −13%, respectively) because they have high brake wear‐derived and significantly reflects the benefits of BEV's RBS. The water‐soluble fraction concentration of metals (induces oxidative stress in the body) was estimated based on aerosol acidity. The reduction of SOx, NOx, and NH3 emissions from on‐road and thermal power plants slightly changed the aerosol acidity (pH ± 0.2). However, it had a negligible effect on water‐soluble metal concentrations (maximum +2% for Fe and +0.5% for Cu and Zn). Therefore, the metal emissions reduction was more important than gaseous pollutants in decreasing the water‐soluble metals that induces respiratory oxidative stress and passenger car electrification and lightweighting were effective means of achieving this. Plain Language Summary: Water‐soluble metals in PM2.5 induce respiratory oxidative stress. Gaseous pollutants increase the aerosol acidity and contribute to metal dissolution. In this study, the effects of renewable energy shifting, passenger car electrification, and lightweighting by 2050 on the atmospheric concentrations of PM2.5 total mass, Fe, Cu, and Zn and aerosol acidity in Japan were evaluated using atmospheric simulation. Since the regenerative braking system (RBS) of battery electric vehicles (BEVs) have lower brake wear emissions than those of conventional vehicles, the penetration of BEVs was effective in reducing the concentrations of Fe and Cu, which have high brake wear dependence (−13% and −18%, respectively, in urban area). Current BEVs increase tire and road wear and resuspension‐derived PM emissions due to their heavy weight, which can be avoided by lightweighting technologies through 2050. The reduction of gaseous pollutants from thermal power plants and on‐road slightly changed aerosol acidity, but the effect on water‐soluble metal concentrations was small. Therefore, it was suggested that reducing primary metal emissions is more important than gaseous pollutants in decreasing concentration of water‐soluble metals that are harmful to the respiratory system, and that vehicle electrification and lightweighting are effective means for that. Key Points: Vehicle electrification effectively reduced the concentrations of PM2.5‐Fe and Cu, which are toxic to respiratory oxidative stressThe lightweighting of battery electric vehicles reduced all non‐exhaust PM from tire, brake, road wear, and resuspensionChanges in aerosol acidity due to gaseous pollutants reduction had little effect on the water‐solubility of metals [ABSTRACT FROM AUTHOR]

Exposure to particulate matter less than 2.5 µm in diameter (PM2.5) is a cause of concern in cities and major emission regions of northern India. An intensive field campaign involving the states of Punjab, Haryana and Delhi national capital region (NCR) was conducted in 2022 using 29 Compact and Useful PM2.5 Instrument with Gas sensors (CUPI-Gs). Continuous observations show that the PM2.5 in the region increased gradually from < 60 µg m−3 in 6–10 October to up to 500 µg m−3 on 5–9 November, which subsequently decreased to about 100 µg m−3 in 20–30 November. Two distinct plumes of PM2.5 over 500 µg m−3 are tracked from crop residue burning in Punjab to Delhi NCR on 2–3 November and 10–11 November with delays of 1 and 3 days, respectively. Experimental campaign demonstrates the advantages of source region observations to link agricultural waste burning and air pollution at local to regional scales. [ABSTRACT FROM AUTHOR]

A regional meteorology–chemistry model was used to evaluate the impact of battery electric vehicles (BEV) penetration on summer O3 concentrations in Kanto (Japan's most populous region). When all passenger cars shifted to BEVs, daytime ozone (O3) concentrations decreased over a wide area. The reduction of vehicle exhaust reduced O3 in inland suburban areas (NOx‐limited) and the reduction of gasoline fuel evaporation from vehicles and gas stations reduced O3 in urban areas (volatile organic compound (VOC)‐limited). The maximum location of maximum daily 8‐hr average O3 (MDA8hO3) sensitivity (−5%; −5 ppb) was at midway between urban and suburban areas, to which the reduction of exhaust and fuel evaporation contributed equally, respectively. The additional emissions from thermal power plants due to BEV's night‐charging could cause up to ±5% sensitivity to next‐day surface O3 concentrations topically. Depending on the O3 sensitivity regime (NOx‐ or VOC‐limited), additional NOx‐rich plumes from rural (urban) power plants tended to increase (decrease) the next day's O3. However, the spatial distribution of the regime varies temporally depending on such as NOx/VOC emission ratios and meteorological conditions. This study indicated that the distribution of negative (positive) O3 sensitivity by NOx‐rich plume is consistent with that of small (large) H2O2/HNO3 concentration ratios, indicating that H2O2/HNO3 works well as an indicator to discriminate O3 sensitivity regimes. Utilization of the H2O2/HNO3 indicator would enable regime distribution predictions without sensitivity simulations with varying NOx and VOC emissions, which would contribute to reducing computational costs. Plain Language Summary: Ozone (O3), which causes respiratory health effects, is formed in the atmosphere by its precursors NOx and volatile organic compound (VOC). Conventional gasoline vehicle exhaust is a major source of NOx and VOC, gasoline fuel VOC evaporate from vehicles and gas stations and thermal power plants emit mainly NOx. This study evaluated the impact of BEV penetration on summer O3 concentrations in Kanto using numerical simulation. When all passenger cars shifted to BEVs, daytime O3 concentrations decreased over a wide area in Kanto (up to −5%). The additional emissions from thermal power plants due to BEV night‐charging had a ±5% impact on next‐day O3 concentration topically. O3 has a NOx‐ or VOC‐sensitive region (called O3 sensitivity regime), and different effective NOx‐VOC emission measure. The above sensitivity was explained by the emission change by BEV shifting and the O3 sensitivity regime distribution. The spatial distribution of the regime varies temporally depending on NOx/VOC emission ratios and meteorological conditions. This study also indicated that H2O2/HNO3 is a useful indicator for its discrimination. Utilization of the H2O2/HNO3 indicator would enable regime distribution predictions without sensitivity simulations with varying NOx and VOC emissions, which is originally required, and would contribute to reducing computational costs. Key Points: The impact of battery electric vehicle (BEV) penetration on summer O3 concentrations in the Kanto region of Japan was evaluatedDaytime O3 decreased in both urban and inland suburban areasAdditional NOx emission from power plants due to night‐charging for BEV affected next day daytime O3 depending on meteorological conditions [ABSTRACT FROM AUTHOR]

Identifying the change of city‐scale extreme precipitation (EP) under the "new normal" of global climate is critical for various urban risk assessments. Here, we investigate the change of hourly EP caused by warmer climate regimes in a large urban agglomeration in midlatitude, Tokyo, Japan. We use pseudo‐global warming dynamical downscaling approach with a convection‐permitting regional climate model considering two Representative Concentration Pathways scenarios 8.5 and 4.5 to simulate the August climate for the present (2005–2014) and the future time (up to 2100). The results show a substantial enhancement of local hourly precipitation regarding both frequency and intensity. Framing the change with Clausius‐Clapeyron (CC) scaling relation, which is of approximately 7% per K warming, we confirmed the paradigm of "extreme gets more extreme" in the future local hourly precipitation. The 0.99 quantile precipitation is intensified at the super CC scaling rate (3 CC); whereas the intensification of lower‐quantile precipitation is at the sub‐CC rate. The EP intensification is much stronger than that reported for a tropical city, highlighting geographical diversity in precipitation response to the global warming effect. The EP intensification is attributed to the global‐warming caused convective inhibition (CIN) enhancement. Enhanced CIN temporarily delays weak convections to initiate, allowing it to build up further, and when the convection does trigger, it becomes intense. Plain Language Summary: Limited knowledge exists over how extreme precipitation (EP) in cities will change under the global warming effect. Here taking Tokyo, Japan, as a case study, we investigate the response of local precipitation to warmer climates using a fine‐resolution regional climate model, which can explicitly represent convection processes and urban effects. We found that precipitation will substantially enhance in both frequency and intensity, but the enhancement is not uniform among precipitation types. Heavy precipitation is found to intensify more than moderate and light rainfall. This result highlights a new normal of "extreme gets more extreme." The EP intensification is found much stronger than that reported for a tropical city, highlighting the geographical diversity in global warming effect on localized precipitation. The EP intensification is attributed to the global warming caused convective inhibition (CIN) enhancement. Enhanced CIN temporarily delays weak convections to initiate, allowing it to build up further, and when the convection does trigger, it becomes intense. Key Points: A paradigm of "extreme gets more extreme" in city‐scale hourly precipitation under warming climates is confirmedExtreme precipitation is more intensified in midlatitude than that reported for a tropical cityConvective inhibition temporarily suppresses weak convection to initiate, and when the convection does trigger, it becomes intense [ABSTRACT FROM AUTHOR]

A fleet of thirteen in-service global container ships continuously measured the air dose rates over the North Pacific after the Fukushima Daiichi Nuclear Power Station (FDNPS) accident. The results showed that the elevated air dose rates over the Port of Tokyo and the FDNPS emissions are significantly correlated (log(emission fluxes) = 54.98 x (air dose rates) (R = 0.95, P-value<0.01), and they are also significantly correlated with the Tsukuba deposition fluxes (log(deposition fluxes) = 0.47 + 30.98 (air dose rates) (R = 0.91, P-value<0.01). These results demonstrate the direct impact of the FDNPS emissions on the depositions of radionuclides and the air dose rates over the Port of Tokyo. Over the North Pacific, the correlation equations are log(emission fluxes) = -2.72 + 202.36 x (air dose rates over the northwestern Pacific) (R = 0.40, P-value<0.01), and log(emission fluxes) = -0.55 + 80.19 x (air dose rates over the northeastern Pacific) (R = 0.29, P-value = 0.0424). These results indicate that the resuspension of the deposited radionuclides have become a dominant source in the transport of radionuclides across the North Pacific. Model simulations show underestimated air dose rates during the periods of 22-25 March 2011 and 27-30 March 2011 indicating the lack of mechanisms, such as the resuspension of radionuclides, in the model. [ABSTRACT FROM AUTHOR]

Biomass burning (BB) events are occurring globally with increasing frequency, and their emissions are having more impacts on human health and climate. Large ash particles are recognized as a BB product with major influences on soil and water environments. However, fine‐ash particles, which have diameters smaller than several microns and characteristic morphologies and compositions (mainly Ca and Mg carbonates), have not yet been explicitly considered as a major BB aerosol component either in field observations or climate models. This study measured BB aerosol samples using transmission electron microscopy (TEM) and ion chromatography during the Fire Influence on Regional to Global Environments and Air Quality (FIREX‐AQ) campaign. We show that significant amounts of fine ash‐bearing particles are transported >100 km from their fire sources. Our environmental chamber experiments suggest that they can act as cloud condensation and ice nuclei. We also found considerable amounts of fine ash‐bearing particles in the TEM samples collected during previous campaigns (Biomass Burning Observation Project and Megacity Initiative: Local and Global Research Observations). These ash particles are commonly mixed with organic matter and make up ∼8% and 5% of BB smoke by number and mass, respectively, in samples collected during the FIREX‐AQ campaign. The measured ash‐mass concentrations are approximately five times and six times greater than those of BB black carbon and potassium, respectively, scaling to an estimated global emission of 11.6 Tg yr−1 with a range of 8.8–16.3 Tg yr−1. Better characterization and constraints on these fine ash‐bearing particles will improve BB aerosol measurements and strengthen assessments of BB impacts on human health and climate. Plain Language Summary: Biomass burning (BB) events occur globally and impact climate and human health. Ash particles larger than ∼10 μm are well known as the main products of BB that contaminate the soil and water near the source regions. On the other hand, ash particles having diameters smaller than several microns, which are inhalable and can be transported long distances, are not yet recognized as a major aerosol component of BB smoke. This study reveals that such fine ash‐bearing particles are abundant in number (∼8%) and mass (∼5%) within BB smoke. The global emission of fine ash particles is estimated to be 11.6 Tg yr−1 with a range of 8.8–16.3 Tg yr−1. By considering their abundance and properties, we will strengthen assessments of BB impacts on human health and climate. Key Points: Ash‐bearing particles with diameters smaller than several microns can be one of the major aerosol components in biomass burning (BB) smokeFine ash‐bearing particles can act as cloud condensation or ice nuclei and influence cloud propertiesThe global emission of fine ash aerosol mass from BB is estimated to be ∼11.6 Tg yr−1 [ABSTRACT FROM AUTHOR]

Resuspension of 137 Cs from the contaminated ground surface to the atmosphere is essential for understanding the environmental behaviors of 137 Cs and estimating external and inhalation exposure of residents. Kajino et al. (2016) assessed the 137 Cs resuspension flux from bare soil and forest ecosystems in eastern Japan in 2013 using a numerical simulation constrained by surface air concentration measurements. However, the simulation was found to underestimate the observed deposition amounts by 2 orders of magnitude. The reason for this underestimation is that the simulation assumed that resuspended 137 Cs is carried by submicron aerosols, which have low deposition rates. Based on the observational indications that soil dust and bioaerosols are the major carriers of resuspended 137 Cs, a new simulation is performed with higher deposition rates constrained by both surface concentrations and deposition amounts. In the new estimation, the total areal annual resuspension of 137 Cs in 2013 is 25.7 TBq, which is equivalent to 0.96 % of the initial deposition (2.68 PBq). Due to the rapid deposition rates, the annual redeposition amount is also large at 10.6 TBq, approximately 40 % of the resuspended 137 Cs. The resuspension rate through the atmosphere (0.96 % yr -1) seems slow, but it (2.6 × 10 -5 d -1) may not be negligibly small compared to the actual decreasing trend of the ambient gamma dose rate obtained in Fukushima Prefecture after the radioactive decay of 137 Cs plus 134 Cs in 2013 is subtracted (1.0–7.9 × 10 -4 d -1): resuspension can account for 1 %–10 % of the decreasing rate due to decontamination and natural decay through land surface processes. The current simulation underestimated the 137 Cs deposition in Fukushima city in winter by more than an order of magnitude, indicating the presence of additional resuspension sources. The site of Fukushima city is surrounded by major roads. Heavy traffic on wet and muddy roads after snow removal operations could generate superlarge (approximately 100 µ m in diameter) road dust or road salt particles, which are not included in the model but might contribute to the observed 137 Cs at the site. [ABSTRACT FROM AUTHOR]

After the Fukushima nuclear accident, atmospheric 134 Cs and 137 Cs measurements were taken in Fukushima city for 8 years, from March 2011 to March 2019. The airborne surface concentrations and deposition of radiocesium (radio-Cs) were high in winter and low in summer; these trends are the opposite of those observed in a contaminated forest area. The effective half-lives of 137 Cs in the concentrations and deposition before 2015 (0.754 and 1.30 years, respectively) were significantly shorter than those after 2015 (2.07 and 4.69 years, respectively), which was likely because the dissolved radio-Cs was discharged from the local terrestrial ecosystems more rapidly than the particulate radio-Cs. In fact, the dissolved fractions of precipitation were larger than the particulate fractions before 2015, but the particulate fractions were larger after 2016. X-ray fluorescence analysis suggested that biotite may have played a key role in the environmental behavior of particulate forms of radio-Cs after 2014. However, the causal relationship between the seasonal variations in particle size distributions and the possible sources of particles is not yet fully understood. The current study also proposes an evaluation method of the consistency of a numerical model for radio-Cs resuspension and suggests that improvements to the model are necessary. [ABSTRACT FROM AUTHOR]

The NASA/AErosol RObotic NETwork field campaign Distributed Regional Aerosol Gridded Observation Networks/Joint work to the AerosoL Properties and Process Simulations was conducted from March 2020 to May 2021 in Nagano, Japan. Twelve sun photometers were installed around Nagano prefecture. The effects of topography on aerosols were studied using observations and simulations. In this study, a regional chemical transport model (SCALE‐Chem) was employed. Three numerical experiments were conducted: E1 (control experiment), E2 (E1 without topography), and E3 (E1 with removal of all anthropogenic emissions over Nagano prefecture). In E2, the terrain effect was not considered; the difference between E1 and E2 indicated the influence of mountains. The differences between E1 and E3 evaluate the local emission effect. In some cases, the mountainous terrain seemed to have suppressed aerosol inflow (i.e., reduced aerosol concentration), while in other cases, the mountains contributed to aerosol retention on days when aerosols tended to accumulate in mountain basins due to local emissions. Thus, while mountains prevent the inflow of aerosols from outside, they also contribute to increased aerosol concentration in the basin. Naturally, more significant effects are produced by meteorological conditions and the presence or absence of transboundary pollution from the outside. From observations and model simulations, we found that the aerosol concentration was not high around the J‐ALPS site because of the mountain effect that prevents advection from the outside, even when transboundary pollution was observed in Japan in March 2020. Plain Language Summary: Aerosol observations by the NASA/AErosol RObotic NETwork field campaign were conducted in the mountainous regions of Japan from March 2020 to May 2021. This field campaign is called Distributed Regional Aerosol Gridded Observation Network/Joint work to the AerosoL Properties and Process Simulation because the target area includes the mountains known as the Japanese Alps. In this study, we investigated how mountains affect aerosol distribution by using simulations with the regional chemical transport model SCALE‐Chem in conjunction with observational data in mountainous regions. To investigate the effect of mountains, simulations were conducted with and without mountains. In addition, to investigate the effect of local sources, we compared simulations with and without anthropogenic emissions in the target area. The simulation results showed that the mountains blocked aerosols and created a basin effect by increasing the aerosol concentration near the surface. Furthermore, averaged throughout March 2020, the effect of the mountains blocking aerosols was greater than the effect of the mountains increasing aerosol concentrations near the surface. This finding suggests that the blocking effect of the surrounding mountains prevented an increase in aerosol concentrations at the J‐ALPS site even on days when transboundary pollution from mainland China arrived in Japan. Key Points: To investigate the effect of mountains on aerosols, a regional model was implemented for field campaign over a Japanese mountain regionThis study found that, mountains have a blocking effect on advection aerosols, but also increase aerosol concentrations in basinsThe J‐ALPS sites showed that, the mountain effect prevented external advection, even on days with widespread transboundary pollution [ABSTRACT FROM AUTHOR]

Resuspension of 137Cs from the contaminated ground surface to the atmosphere is essential for understanding the environmental behaviors of 137Cs and estimating external and inhalation exposure of residents. Kajino et al. (2016) assessed the 137Cs resuspension flux from bare soil and forest ecosystems in East Japan in 2013 using a numerical simulation constrained by surface air concentration measurements. However, the simulation was found to underestimate the observed deposition amounts by two orders of magnitude. The reason for this underestimation is that the simulation assumed that resuspended 137Cs is carried by submicron aerosols, which have low deposition rates. Based on the observational indications that soil dust and bioaerosols are the major carriers of resuspended 137Cs, a new simulation is performed with higher deposition rates constrained by both surface concentrations and deposition amounts. In the new estimation, the areal total annual resuspension of 137Cs in 2013 is 25.7 TBq, which is equivalent to 0.96 % of the initial deposition (2.68 PBq). Due to the rapid deposition rates, the annual redeposition amount is also large at 10.6 TBq, approximately 40 % of the resuspended 137Cs. The resuspension rate through the atmosphere (0.96 % y-1) seems slow, but it (2.6 × 10-5 d-1) may not be negligibly small compared to the actual decreasing trend of the ambient gamma dose rate obtained in Fukushima Prefecture after the radioactive decay of 137Cs plus 134Cs in 2013 is subtracted (1.0-7.9 × 10-4 d-1): Resuspension can account for 1-10 % of the decreasing rate due to decontamination and natural decay through land surface processes. The current simulation underestimated the 137Cs deposition in Fukushima city in winter by more than an order of magnitude, indicating the presence of additional resuspension sources. The site of Fukushima city is surrounded by major roads. Heavy traffic on wet and muddy roads after snow removal operations could generate superlarge (approximately 100 µm in diameter) road dust or road salt particles, which is not included in the model but might contribute to the observed 137Cs at the site. [ABSTRACT FROM AUTHOR]

After the Fukushima nuclear accident, atmospheric 134Cs and 137Cs measurements were taken in Fukushima city for eight years, from March 2011 to March 2019. The surface air concentrations and deposition of radio-Cs were high in winter and low in summer; these trends are the opposite of those observed in a contaminated forest area. The half-lives of 137Cs in the concentrations and deposition before 2015 (275 d and 1.11 y) were significantly shorter than those after 2015 (756 d and 4.69 y). The dissolved fractions of precipitation were larger than the particulate fractions before 2015, but the particulate fractions were larger after 2016. The half-lives of 137Cs in the concentrations and deposition were shorter before 2015, probably because the dissolved radio-Cs was discharged from the local terrestrial ecosystems more rapidly than the particulate radio-Cs. X-ray fluorescence analysis suggested that biotite may have played a key role in the environmental behavior of particulate forms of radio-Cs after 2014. However, the causal relationship between the seasonal variations in particle size distributions and the possible sources of particles is not yet fully understood. The current study also proposes a method of evaluating the consistency of a numerical model for radio-Cs resuspension and suggests that improvements to the model are necessary. [ABSTRACT FROM AUTHOR]

Asia has attracted research attention because it has the highest anthropogenic emissions in the world, and the Model Inter-Comparison Study for Asia (MICS-Asia) phase III was carried out to foster our understanding of the status of air quality over Asia. This study analyzed wet deposition in southeast Asian countries (Myanmar, Thailand, Lao People's Democratic Republic (PDR), Cambodia, Vietnam, the Philippines, Malaysia, and Indonesia) with the aim of providing insights into the seasonal variation of wet deposition. Southeast Asia was not fully considered in MICS-Asia phase II due to a lack of observational data; however, the analysis period of MICS-Asia III, namely the year 2010, is covered by ground observations of the Acid Deposition Monitoring Network in East Asia (EANET), and the coordinated simulation domain was extended to cover these observation sites. The analyzed species are wet depositions of S (sulfate aerosol, sulfur dioxide (SO 2), and sulfuric acid (H 2 SO 4)), N (nitrate aerosol, nitrogen monoxide (NO), nitrogen dioxide (NO 2), and nitric acid (HNO 3)), and A (ammonium aerosol and ammonia (NH 3)). The wet deposition simulated with seven models driven by a unified meteorological model in MICS-Asia III was used with the ensemble approach, which effectively modulates the differences in performance among models. By comparison with EANET observations, although the seven models generally captured the wet depositions of S, N, and A, there were difficulties capturing these in some cases. Considering the model performance for ambient aerosol concentrations over southeast Asia, this failure of models is considered to be related to the difficulty in capturing the precipitation in southeast Asia, especially during the dry and wet seasons. Generally, meteorological fields overestimate the precipitation during the dry season, which leads to the overestimation of wet deposition during this season. To overcome this, a precipitation-adjusted approach that scaled the modeled precipitation to the observed value was applied, and it was demonstrated that the model performance was improved. Satellite measurements were also used to adjust for precipitation data, which adequately accounted for the spatiotemporal precipitation patterns, especially in the dry season. As the statistical scores were mostly improved by this adjustment, the estimation of wet deposition with precipitation adjustment was considered to be superior. To utilize satellite measurements, the spatial distribution of wet deposition was revised. Based on this revision, it was found that Vietnam, Malaysia, and Indonesia were upward corrected, and Myanmar, Thailand, Lao PDR, Cambodia, and the Philippines were downward-corrected; these corrections were up to ±40 %. The improved accuracy of precipitation amount was key to estimating wet deposition in this study. These results suggest that the precipitation-adjusted approach has the potential to obtain accurate estimates of wet deposition through the fusion of models and observations. [ABSTRACT FROM AUTHOR]

COVID-19 related restrictions lowered particulate matter and trace gas concentrations across cities around the world, providing a natural opportunity to study effects of anthropogenic activities on emissions of air pollutants. In this paper, the impact of sudden suspension of human activities on air pollution was analyzed by studying the change in satellite retrieved NO2 concentrations and top-down NOx emission over the urban and rural areas around Delhi. NO2 was chosen for being the most indicative of emission intensity due to its short lifetime of the order of a few hours in the planetary boundary layer. We present a robust temporal comparison of Ozone Monitoring Instrument (OMI) retrieved NO2 column density during the lockdown with the counterfactual baseline concentrations, extrapolated from the long-term trend and seasonal cycle components of NO2 using observations during 2015 to 2019. NO2 concentration in the urban area of Delhi experienced an anomalous relative change ranging from 60.0% decline during the Phase 1 of lockdown (March 25–April 13, 2020) to 3.4% during the post-lockdown Phase 5. In contrast, we find no substantial reduction in NO2 concentrations over the rural areas. To segregate the impact of the lockdown from the meteorology, weekly top-down NOx emissions were estimated from high-resolution TROPOspheric Monitoring Instrument (TROPOMI) retrieved NO2 by accounting for horizontal advection derived from the steady state continuity equation. NOx emissions from urban Delhi and power plants exhibited a mean decline of 72.2% and 53.4% respectively in Phase 1 compared to the pre-lockdown business-as-usual phase. Emission estimates over urban areas and power-plants showed a good correlation with activity reports, suggesting the applicability of this approach for studying emission changes. A higher anomaly in emission estimates suggests that comparison of only concentration change, without accounting for the dynamical and photochemical conditions, may mislead evaluation of lockdown impact. Our results shall also have a broader impact for optimizing bottom-up emission inventories. [ABSTRACT FROM AUTHOR]

This study provides comparisons of aerosol representation methods incorporated into a regional-scale nonhydrostatic meteorology–chemistry model (NHM-Chem). Three options for aerosol representations are currently available: the five-category non-equilibrium (Aitken, soot-free accumulation, soot-containing accumulation, dust, and sea salt), three-category non-equilibrium (Aitken, accumulation, and coarse), and bulk equilibrium (submicron, dust, and sea salt) methods. The three-category method is widely used in three-dimensional air quality models. The five-category method, the standard method of NHM-Chem, is an extensional development of the three-category method and provides improved predictions of variables relating to aerosol–cloud–radiation interaction processes by implementing separate treatments of light absorber and ice nuclei particles, namely, soot and dust, from the accumulation- and coarse-mode categories (implementation of aerosol feedback processes to NHM-Chem is still ongoing, though). The bulk equilibrium method was developed for operational air quality forecasting with simple aerosol dynamics representations. The total CPU times of the five-category and three-category methods were 91 % and 44 % greater than that of the bulk method, respectively. The bulk equilibrium method was shown to be eligible for operational forecast purposes, namely, the surface mass concentrations of air pollutants such as O3 , mineral dust, and PM2.5. The simulated surface concentrations and depositions of bulk chemical species of the three-category method were not significantly different from those of the five-category method. However, the internal mixture assumption of soot/soot-free and dust/sea salt particles in the three-category method resulted in significant differences in the size distribution and hygroscopicity of the particles. The unrealistic dust/sea salt complete mixture of the three-category method induced significant errors in the prediction of the mineral dust-containing cloud condensation nuclei (CCN), which alters heterogeneous ice nucleation in cold rain processes. The overestimation of soot hygroscopicity by the three-category method induced errors in the BC-containing CCN, BC deposition, and light-absorbing aerosol optical thickness (AAOT). Nevertheless, the difference in AAOT was less pronounced with the three-category method because the overestimation of the absorption enhancement was compensated by the overestimation of hygroscopic growth and the consequent loss due to in-cloud scavenging. In terms of total properties, such as aerosol optical thickness (AOT) and CCN, the results of the three-category method were acceptable. [ABSTRACT FROM AUTHOR]

The aerosol oxidative potential (OP) is considered to better represent the acute health hazards of aerosols than the mass concentration of fine particulate matter (PM2.5). The proposed major contributors to OP are water soluble transition metals and organic compounds, but the relative magnitudes of these compounds to the total OP are not yet fully understood. In this study, as the first step toward the numerical prediction of OP, the cumulative OP (OPtm*) based on the top five key transition metals, namely, Cu, Mn, Fe, V, and Ni, was defined. The solubilities of metals were assumed constant over time and space based on measurements. Then, the feasibility of its prediction was verified by comparing OPtm* values based on simulated metals to that based on observed metals in East Asia. PM2.5 typically consists of primary and secondary species, while OPtm* only represents primary species. This disparity caused differences in the domestic contributions of PM2.5 and OPtm*, especially in large cities in western Japan. The annual mean domestic contributions of PM2.5 were 40%, while those of OPtm* ranged from 50 to 55%. Sector contributions to the OPtm* emissions in Japan were also assessed. The main important sectors were the road brake and iron–steel industry sectors, followed by power plants, road exhaust, and railways. [ABSTRACT FROM AUTHOR]

The dispersion and deposition of radio‐cesium (137Cs) carried by two types (type A and type B) of water‐insoluble Cs‐bearing solid microparticles (CsMPs) released due to the Fukushima nuclear accident were simulated for the first time. The presence of type B CsMPs (70–400 μm found in soil and 1–5 μm found in air), associated with the hydrogen explosion of Unit 1 in the afternoon of March 12, could partly explain the simulated underestimation of total deposition over land by assuming that 100% of the Cs carriers were water‐soluble submicron particles (WSPs). Type A CsMPs (0.1–10 μm), released from Units 2 or 3 in the midnight between March 14 and 15, traveled over the Kanto Plain, the most populated plain in Japan. Differences in the size distribution of type A CsMPs altered the surface air concentration over Kanto substantially, by up to more than one order of magnitude. The major deposition mechanisms varied among dry, wet, and fog (and/or cloud) depositions depending on the size distribution and locations. The simulated activity fractions due to the CsMPs in the total deposition were compared to those observed in surface soil for the first time. The observations could be explained by the simulations for the locations under the influence of type B CsMPs. However, the simulations were substantially underestimated for the locations influenced by type A CsMPs. There could be more fractions of type A CsMPs emission in the source term and/or the simulated deposition rates of type A CsMPs were underestimated. Key Points: The regional impacts of two types (A and B) of Cs‐bearing solid microparticles (CsMPs) were numerically examined for the first timeType B CsMPs could partly explain the underestimation of simulated total deposition over landThe environmental behaviors of type A CsMPs could vary substantially depending on size [ABSTRACT FROM AUTHOR]

Asia has attracted research attention because it has the highest anthropogenic emissions in the world, and the Model Inter-Comparison Study for Asia (MICS-Asia) Phase III was carried out to foster our understanding on the status of air quality over Asia. This study analyzed wet deposition in Southeast Asian countries (Myanmar, Thailand, Lao People's Democratic Republic (PDR), Cambodia, Vietnam, the Philippines, Malaysia, and Indonesia) with the aim of providing insights into the seasonal variation of wet deposition. Southeast Asia was not fully considered in MICS-Asia Phase II due to a lack of observational data; however, the analysis period of MICS-Asia III, namely, the year 2010, is covered by ground observations of the Acid Deposition Monitoring Network in East Asia (EANET), and the coordinated simulation domain was extended to cover these observation sites. The analyzed species are wet depositions of S (sulfate aerosol, sulfur dioxide (SO2), and sulfuric acid (H2SO4)), N (nitrate aerosol, nitrogen monoxide (NO), nitrogen dioxide (NO2), and nitric acid (HNO3)), and A (ammonium aerosol and ammonia (NH3)). The wet deposition simulated with seven models driven by unified meteorological model in MICS-Asia III was used with the ensemble approach, which effectively modulates the differences in performance among models. By comparison with EANET observations, although the seven models generally captured the wet depositions of S, N, and A, there were difficulties capturing these in some cases. This failure of models is considered to be related to the difficulty in capturing the precipitation in Southeast Asia, especially during the dry and wet seasons. To overcome this, a precipitation-adjusted approach which scaling the modeled precipitation to the observed value was applied, and it was demonstrated that the model performance was improved. Satellite measurements were also used to adjust for precipitation data, which worked well to account for spatio-and-temporal precipitation patterns, especially in the dry season. As the statistical scores were mostly improved by this adjustment, the estimation of wet deposition with precipitation adjustment was considered to be superior. To utilize satellite measurements, the spatial distribution of wet deposition was revised. Based on this revision, it was found that Vietnam, Malaysia, and Indonesia were upward-corrected and Myanmar, Thailand, Lao PDR, Cambodia, and the Philippines were downward-corrected; these corrections were up to ±40%. The improved accuracy of precipitation amount was key to estimating wet deposition in this study. These results suggest that the precipitation-adjusted approach has the potential to obtain accurate estimates of wet deposition through the fusion of models and observations. [ABSTRACT FROM AUTHOR]

We have measured artificial radionuclides, such as 90Sr and 137Cs, in atmospheric depositions since 1957 in Japan. We observed the variations in 90Sr and 137Cs, which were emitted from atmospheric nuclear tests and nuclear power plant accidents, due to their diffusion, deposition, and resuspension. In March 2011, the Fukushima Daiichi Nuclear Power Plant accident occurred in Japan, and significant increases in 90Sr and 137Cs were detected at our main site in Tsukuba, Ibaraki. Our continual observations revealed that the 137Cs monthly deposition rate in 2018 declined to ~ 1/8100 of the peak level, but it remained more than ~ 400 times higher than that before the accident. Chemical analysis suggested that dust particles were the major carriers of 90Sr and 137Cs during the resuspension period at our main site. Presently, the effective half-life for 137Cs deposition due to radioactive decay and other environmental factors is 4.7 years. The estimation suggests that approximately 42 years from 2011 are required to reduce the atmospheric 137Cs deposition to a state similar to that before the accident. The current 90Sr deposition, on the other hand, shows the preaccident seasonal variation, and it has returned to the same radioactive level as that before the accident. [ABSTRACT FROM AUTHOR]

Emission inventories of anthropogenic transition metals, which contribute to aerosol oxidative potential (OP), in Asia (Δx = 0.25°, monthly, 2000–2008) and Japan (Δx = 2 km, hourly, mainly 2012) were developed, based on bottom‐up inventories of particulate matters and metal profiles in a speciation database for particulate matters. The new inventories are named Transition Metal Inventory (TMI)‐Asia v1.0 and TMI‐Japan v1.0, respectively. It includes 10 transition metals in PM2.5 and PM10, which contributed to OP based on reagent experiments, namely, Cu, Mn, Co, V, Ni, Pb, Fe, Zn, Cd, and Cr. The contributions of sectors in the transition metals emission in Japan were also investigated. Road brakes and iron‐steel industry are primary sources, followed by other metal industry, navigation, incineration, power plants, and railway. In order to validate the emission inventory, eight elements such as Cu, Mn, V, Ni, Pb, Fe, Zn, and Cr in anthropogenic dust and those in mineral dust were simulated over East Asia and Japan with Δx = 30 km and Δx = 5 km domains, respectively, and compared against the nation‐wide seasonal observations of PM2.5 elements in Japan and the long‐term continuous observations of total suspended particles (TSPs) at Yonago, Japan in 2013. Most of the simulated elements generally agreed with the observations, while Cu and Pb were significantly overestimated. This is the first comprehensive study on the development and evaluation of emission inventory of OP active elements, but further improvement is needed. Plain Language Summary: Aerosol oxidative potential (OP) has been focused on as a better health hazard of aerosols than PM2.5. OP is quantified by in vitro assays to mimic the in vivo generation of superoxide radicals to cause oxidative stress on human cells. OP has been reported to be more strongly associated with cardiorespiratory outcomes than PM2.5. Transition metals ions, organics, and elementary carbon, together with their interactions, have been reported as important compounds, but the relative magnitudes of contributions to total OP have not yet been fully understood. In this study, as a first step, we developed emission inventories and a numerical model to predict OP active transition metals in Asia and Japan and compared them with observations. We also quantitatively derived the major emission sources for the important metals such as Cu, Mn, Fe, V, and Ni in Japan. The current study is the first step toward better predicting the health hazard of aerosols. As the next step in the future, water solubility of metals and OP active organics, together with their interactions, should be considered. Key Points: Emission inventories of transition metals, which contribute to aerosol oxidative potential (OP), in Asia and Japan were developedMost of simulated elements (Mn, V, Ni, Fe, Zn, and Cr) agreed with observation, while Cu and Pb were significantly overestimatedRoad brakes and iron‐steel industry are primary sources, followed by metal industry, navigation, incineration, power plants, and railway [ABSTRACT FROM AUTHOR]

Atmospheric nitrogen deposition in China has attracted public attention in recent years due to the increasing anthropogenic emission of reactive nitrogen (Nr) and its impacts on the terrestrial and aquatic ecosystems. However, limited long-term and multisite measurements have restrained the understanding of the mechanism of the Nr deposition and the chemical transport model (CTM) improvement. In this study, the performance of the simulated wet and dry deposition for different Nr species, i.e., particulate NO3- and NH4+ , gaseous NOx , HNO3 and NH3 have been conducted using the framework of Model Inter-Comparison Study for Asia (MICS-Asia) phase III. A total of nine models, including five Weather Research and Forecasting models coupled with the Community Multiscale Air Quality (WRF-CMAQ) models, two self-developed regional models, a global model and a Regional Atmospheric Modeling System coupled with the Community Multiscale Air Quality (RAMS-CMAQ) model have been selected for the comparison. For wet deposition, observation data from 83 measurement sites from the East Asia Acid Deposition Monitoring Network (EANET), Chinese Ecosystem Research Network (CERN), China Agricultural University Deposition Network (CAUDN), National Acid Deposition Monitoring Network (NADMN) and Department of Ecological Environment (DEE) of China have been collected and normalized for comparison with model results. In general, most models show the consistent spatial and temporal variation of both oxidized N (Nox) and reduced N (Nrd) wet deposition in China, with the normalized mean error (NME) at around 50 %, which is lower than the value of 70 % based on EANET observation over Asia. Both the ratio of wet or dry deposition to the total inorganic N (TIN) deposition and the ratios of TIN to their emissions have shown consistent results with the Nationwide Nitrogen Deposition Monitoring Network (NNDMN) estimates. The performance of ensemble results (ENMs) was further assessed with satellite measurements. In different regions of China, the results show that the simulated Nox wet deposition was overestimated in northeastern China (NE) but underestimated in the south of China, namely southeastern (SE) and southwestern (SW) China, while the Nrd wet deposition was underestimated in all regions by all models. The deposition of Nox has larger uncertainties than the Nrd , especially in northern China (NC), indicating the chemical reaction process is one of the most important factors affecting the model performance. Compared to the critical load (CL) value, the Nr deposition in NC, SE and SW reached or exceeded reported CL values and resulted in serious ecological impacts. The control of Nrd in NC and SW and Nox in SE would be an effective mitigation measure for TIN deposition in these regions. The Nr deposition in the Tibetan Plateau (TP) with a high ratio of TIN / emission (∼3.0), indicates a significant transmission from outside. Efforts to reduce these transmissions ought to be paramount due the climatic importance of the Tibetan region to the sensitive ecosystems throughout China. [ABSTRACT FROM AUTHOR]

Delhi, a tropical Indian megacity, experiences one of the most severe air pollution in the world, linked with diverse anthropogenic and biomass burning emissions. First phase of COVID-19 lockdown in India, implemented during 25 March to 14 April 2020 resulted in a dramatic near-zeroing of various activities (e.g. traffic, industries, constructions), except the "essential services". Here, we analysed variations in the fine particulate matter (PM2.5) over the Delhi-National Capital Region. Measurements revealed large reductions (by 40–70%) in PM2.5 during the first week of lockdown (25–31 March 2020) as compared to the pre-lockdown conditions. However, O3 pollution remained high during the lockdown due to non-linear chemistry and dynamics under low aerosol loading. Notably, events of enhanced PM2.5 levels (300–400 µg m−3) were observed during night and early morning hours in the first week of April after air temperatures fell close to the dew-point (~ 15–17 °C). A haze formation mechanism is suggested through uplifting of fine particles, which is reinforced by condensation of moisture following the sunrise. The study highlights a highly complex interplay between the baseline pollution and meteorology leading to counter intuitive enhancements in pollution, besides an overall improvement in air quality during the COVID-19 lockdown in this part of the world. [ABSTRACT FROM AUTHOR]

This study compares the performance of 12 regional chemical transport models (CTMs) from the third phase of the Model Inter-Comparison Study for Asia (MICS-Asia III) on simulating the particulate matter (PM) over East Asia (EA) in 2010. The participating models include the Weather Research and Forecasting model coupled with Community Multiscale Air Quality (WRF-CMAQ; v4.7.1 and v5.0.2), the Regional Atmospheric Modeling System coupled with CMAQ (RAMS-CMAQ; v4.7.1 and v5.0.2), the Weather Research and Forecasting model coupled with chemistry (WRF-Chem; v3.6.1 and v3.7.1), Goddard Earth Observing System coupled with chemistry (GEOS-Chem), a non-hydrostatic model coupled with chemistry (NHM-Chem), the Nested Air Quality Prediction Modeling System (NAQPMS) and the NASA-Unified WRF (NU-WRF). This study investigates three model processes as the possible reasons for different model performances on PM. (1) Models perform very differently in the gas–particle conversion of sulfur (S) and oxidized nitrogen (N). The model differences in sulfur oxidation ratio (50 %) are of the same magnitude as that in SO42- concentrations. The gas–particle conversion is one of the main reasons for different model performances on fine mode PM. (2) Models without dust emission modules can perform well on PM 10 at non-dust-affected sites but largely underestimate (up to 50 %) the PM 10 concentrations at dust sites. The implementation of dust emission modules in the models has largely improved the model accuracies at dust sites (reduce model bias to -20 %). However, both the magnitude and distribution of dust pollution are not fully captured. (3) The amounts of modeled depositions vary among models by 75 %, 39 %, 21 % and 38 % for S wet, S dry, N wet and N dry depositions, respectively. Large inter-model differences are found in the washout ratios of wet deposition (at most 170 % in India) and dry deposition velocities (generally 0.3–2 cm s -1 differences over inland regions). [ABSTRACT FROM AUTHOR]

The reproducibility of surface wind and tracer transport simulations from high-resolution weather and transport models was studied over complex terrain in wintertime in Japan. The horizontal grid spacing was varied (5-, 3-, and 1-km grids), and radioactive cesium (Cs-137) from the Fukushima nuclear power plant was used as a tracer. Fukushima has complex terrain, such as mountains and valleys. The model results were validated by observations collected from the national networks of the automated meteorological data acquisition system and the hourly air pollution sampling system. The reproducibility depended on the model resolution, topographic complexity, and synoptic weather conditions. Higher model resolution led to higher reproducibility of surface winds, especially in mountainous areas when the Siberian winter monsoon was disturbed. In contrast, the model improvement was negligible or nonexistent over plain/coastal areas when the synoptic field was steady. The statistical scores of the tracer transport simulations often deteriorated as a result of small errors in the plume locations. However, the higher-resolution models advantageously performed better transport simulations in the mountainous areas because of the lower numerical diffusion and higher reproducibility of the mass flux. The reproducibility of the tracer distribution in the valley of the Fukushima mountainous region was dramatically improved with increasing model resolution. In the range of mesoscale model resolutions (commonly 1–10 km), it was concluded that a higher-resolution model is definitely recommended for tracer transport simulations over mountainous terrain. [ABSTRACT FROM AUTHOR]

Dry deposition has an impact on nitrogen status in forest environments. However, the mechanism for the high dry-deposition rates of fine nitrate particles (NO3-) observed in forests remains unknown and is thus a potential source of error in chemical transport models (CTMs). Here, we modified and applied a multilayer land surface model coupled with dry-deposition and aerosol dynamic processes for a temperate mixed forest in Japan. This represents the first application of such a model to ammonium nitrate (NH4NO3) gas–particle conversion (gpc) and the aerosol water uptake of reactive nitrogen compounds. Thermodynamics, kinetics, and dry deposition for mixed inorganic particles are modeled by a triple-moment modal method. Data for inorganic mass and size-resolved total number concentrations measured by a filter pack and electrical low-pressure impactor in autumn were used for model inputs and subsequent numerical analysis. The model successfully reproduces turbulent fluxes observed above the canopy and vertical micrometeorological profiles noted in our previous studies. The sensitivity tests with and without gpc demonstrated clear changes in the inorganic mass and size-resolved total number concentrations within the canopy. The results also revealed that within-canopy evaporation of NH4NO3 under dry conditions significantly enhances the deposition flux of fine- NO3- and fine- NH4+ particles, while reducing the deposition flux of nitric acid gas (HNO3). As a result of the evaporation of particulate NH4NO3 , the calculated daytime mass flux of fine NO3- over the canopy was 15 times higher in the scenario of "gpc" than in the scenario of "no gpc". This increase caused high contributions from particle deposition flux (NO3- and NH4+) to total nitrogen flux over the forest ecosystem (∼39 %), although the contribution of NH3 was still considerable. A dry-deposition scheme coupled with aerosol dynamics may be required to improve the predictive accuracy of chemical transport models for the surface concentration of inorganic reactive nitrogen. [ABSTRACT FROM AUTHOR]

The Model Inter-Comparison Study for Asia (MICS-Asia) phase III was conducted to promote understanding of regional air quality and climate change in Asia, which have received growing attention due to the huge amount of anthropogenic emissions worldwide. This study provides an overview of acid deposition. Specifically, dry and wet deposition of the following species was analyzed: S (sulfate aerosol, sulfur dioxide (SO2), and sulfuric acid (H2SO4)), N (nitrate aerosol, nitrogen monoxide (NO), nitrogen dioxide (NO2), and nitric acid (HNO3)), and A (ammonium aerosol and ammonia (NH3)). The wet deposition simulated by a total of nine models was analyzed and evaluated using ground observation data from the Acid Deposition Monitoring Network in East Asia (EANET). In the phase III study, the number of observation sites was increased from 37 in the phase II study to 54, and southeast Asian countries were newly added. Additionally, whereas the analysis period was limited to representative months of each season in MICS-Asia phase II, the phase III study analyzed the full year of 2010. The scope of this overview mainly focuses on the annual accumulated deposition. In general, models can capture the observed wet deposition over Asia but underestimate the wet deposition of S and A, and show large differences in the wet deposition of N. Furthermore, the ratio of wet deposition to the total deposition (the sum of dry and wet deposition) was investigated in order to understand the role of important processes in the total deposition. The general dominance of wet deposition over Asia and attributions from dry deposition over land were consistently found in all models. Then, total deposition maps over 13 countries participating in EANET were produced, and the balance between deposition and anthropogenic emissions was calculated. Excesses of deposition, rather than of anthropogenic emissions, were found over Japan, northern Asia, and southeast Asia, indicating the possibility of long-range transport within and outside of Asia, as well as other emission sources. To improve the ability of models to capture the observed wet deposition, two approaches were attempted, namely, ensemble and precipitation adjustment. The ensemble approach was effective at modulating the differences in performance among models, and the precipitation-adjusted approach demonstrated that the model performance for precipitation played a key role in better simulating wet deposition. Finally, the lessons learned from the phase III study and future perspectives for phase IV are summarized. [ABSTRACT FROM AUTHOR]

Despite the significant progress in improving chemical transport models (CTMs), applications of these modeling endeavors are still subject to large and complex model uncertainty. The Model Inter-Comparison Study for Asia III (MICS-Asia III) has provided the opportunity to assess the capability and uncertainty of current CTMs in East Asian applications. In this study, we have evaluated the multi-model simulations of nitrogen dioxide (NO2), carbon monoxide (CO) and ammonia (NH3) over China under the framework of MICS-Asia III. A total of 13 modeling results, provided by several independent groups from different countries and regions, were used in this study. Most of these models used the same modeling domain with a horizontal resolution of 45 km and were driven by common emission inventories and meteorological inputs. New observations over the North China Plain (NCP) and Pearl River Delta (PRD) regions were also available in MICS-Asia III, allowing the model evaluations over highly industrialized regions. The evaluation results show that most models captured the monthly and spatial patterns of NO2 concentrations in the NCP region well, though NO2 levels were slightly underestimated. Relatively poor performance in NO2 simulations was found in the PRD region, with larger root-mean-square error and lower spatial correlation coefficients, which may be related to the coarse resolution or inappropriate spatial allocations of the emission inventories in the PRD region. All models significantly underpredicted CO concentrations in both the NCP and PRD regions, with annual mean concentrations that were 65.4 % and 61.4 % underestimated by the ensemble mean. Such large underestimations suggest that CO emissions might be underestimated in the current emission inventory. In contrast to the good skills for simulating the monthly variations in NO2 and CO concentrations, all models failed to reproduce the observed monthly variations in NH3 concentrations in the NCP region. Most models mismatched the observed peak in July and showed negative correlation coefficients with the observations, which may be closely related to the uncertainty in the monthly variations in NH3 emissions and the NH3 gas–aerosol partitioning. Finally, model intercomparisons have been conducted to quantify the impacts of model uncertainty on the simulations of these gases, which are shown to increase with the reactivity of species. Models contained more uncertainty in the NH3 simulations. This suggests that for some highly active and/or short-lived primary pollutants, like NH3 , model uncertainty can also take a great part in the forecast uncertainty in addition to the emission uncertainty. Based on these results, some recommendations are made for future studies. [ABSTRACT FROM AUTHOR]

Satellite sensors are powerful tools to monitor the spatiotemporal variations of air pollutants in large scales, but it has been challenging to detect surface O3 due to the presence of abundant stratospheric and upper tropospheric O3. East Asia is one of the most polluted regions in the world, but anthropogenic emissions such as NOx and SO2 began to decrease in 2010s. This trend was well observed by satellites, but the spatiotemporal impacts of these emission trends on O3 have not been well understood. Recent advancement in a retrieval method for the Ozone Monitoring Instrument (OMI) sensor enabled detection of lower tropospheric O3 and its legitimacy has been validated. In this study, we investigated the statistical significance for the OMI sensor to detect the lower tropospheric O3 responses to the future emission reduction of the O3 precursor gases over East Asia in summer, by utilizing a regional chemistry model. The emission reduction of 10, 25, 50, and 90% resulted in 4.4, 11, 23, and 53% decrease of the areal and monthly mean daytime simulated satellite-detectable O3 (ΔO3), respectively. The fractions of significant areas are 55, 84, 93, and 96% at a one-sided 95% confidence interval. Because of the recent advancement of satellite sensor technologies (e.g., TROPOMI), study on tropospheric photochemistry will be rapidly advanced in the near future. The current study proved the usefulness of such satellite analyses on the lower tropospheric O3 and its perturbations due to the precursor gas emission controls. [ABSTRACT FROM AUTHOR]

Spatiotemporal variations of ozone (O3) and nitrogen oxide (NOx) mixing ratios from 14 state-of-the-art chemical transport models (CTMs) are intercompared and evaluated with O3 observations in East Asia, within the framework of the Model Inter-Comparison Study for Asia Phase III (MICS-Asia III). This study was designed to evaluate the capabilities and uncertainties of current CTMs simulations for Asia and to provide multi-model estimates of pollutant distributions. These models were run by 14 independent groups working in China, Japan, South Korea, the United States and other countries/regions. Compared with the previous phase of MICS-Asia (MICS-Asia II), the evaluation with observations was extended from 4 months to 1 full year across China and the western Pacific Rim. In general, model performance levels for O3 varied widely by region and season. Most models captured the key patterns of monthly and diurnal variation of surface O3 and its precursors in the North China Plain and western Pacific Rim but failed to do so for the Pearl River Delta. A significant overestimation of surface O3 was evident from May to September/October and from January to May over the North China Plain, the western Pacific Rim and the Pearl River Delta. Comparisons drawn from observations show that the considerable diversity in O3 photochemical production partly contributed to this overestimation and to high levels of inter-model variability in O3 for North China. In terms of O3 soundings, the ensemble average of models reproduced the vertical structure for the western Pacific, but overestimated O3 levels to below 800 hPa in the summer. In the industrialized Pearl River Delta, the ensemble average presented an overestimation for the lower troposphere and an underestimation for the middle troposphere. The ensemble average of 13 models for O3 did not always exhibit superior performance compared with certain individual models in contrast with its superior value for Europe. This finding suggests that the spread of ensemble-model values does not represent all of the uncertainties of O3 or that most MICS-Asia III models missed key processes. This study improved the performance of modeling O3 in March at Japanese sites compared with MICS-Asia II. However, it overpredicted surface O3 concentrations for western Japan in July, which was not found by MICS-Asia II. Major challenges still remain with regard to identifying the sources of bias in surface O3 over East Asia in CTMs. [ABSTRACT FROM AUTHOR]

A total of 14 chemical transport models (CTMs) participated in the first topic of the Model Inter-Comparison Study for Asia (MICS-Asia) phase III. These model results are compared with each other and an extensive set of measurements, aiming to evaluate the current CTMs' ability in simulating aerosol concentrations, to document the similarities and differences among model performance, and to reveal the characteristics of aerosol components in large cities over East Asia. In general, these CTMs can well reproduce the spatial–temporal distributions of aerosols in East Asia during the year 2010. The multi-model ensemble mean (MMEM) shows better performance than most single-model predictions, with correlation coefficients (between MMEM and measurements) ranging from 0.65 (nitrate, NO3-) to 0.83 (PM 2.5). The concentrations of black carbon (BC), sulfate (SO42-), and PM 10 are underestimated by MMEM, with normalized mean biases (NMBs) of -17.0 %, - 19.1 %, and - 32.6 %, respectively. Positive biases are simulated for NO3- (NMB = 4.9 %), ammonium (NH4+) (NMB = 14.0 %), and PM 2.5 (NMB = 4.4 %). In comparison with the statistics calculated from MICS-Asia phase II, frequent updates of chemical mechanisms in CTMs during recent years make the intermodel variability of simulated aerosol concentrations smaller, and better performance can be found in reproducing the temporal variations of observations. However, a large variation (about a factor of 2) in the ratios of SNA (sulfate, nitrate, and ammonium) to PM 2.5 is calculated among participant models. A more intense secondary formation of SO42- is simulated by Community Multi-scale Air Quality (CMAQ) models, because of the higher SOR (sulfur oxidation ratio) than other models (0.51 versus 0.39). The NOR (nitric oxidation ratio) calculated by all CTMs has larger values (∼0.20) than the observations, indicating that overmuch NO3- is simulated by current models. NH3 -limited condition (the mole ratio of ammonium to sulfate and nitrate is smaller than 1) can be successfully reproduced by all participant models, which indicates that a small reduction in ammonia may improve the air quality. A large coefficient of variation (CV > 1.0) is calculated for simulated coarse particles, especially over arid and semi-arid regions, which means that current CTMs have difficulty producing similar dust emissions by using different dust schemes. According to the simulation results of MMEM in six large Asian cities, different air-pollution control plans should be taken due to their different major air pollutants in different seasons. The MICS-Asia project gives an opportunity to discuss the similarities and differences of simulation results among CTMs in East Asian applications. In order to acquire a better understanding of aerosol properties and their impacts, more experiments should be designed to reduce the diversities among air quality models. [ABSTRACT FROM AUTHOR]

To assess the uncertainty of meteorological simulations in the transport and deposition of radio‐Cs release associated with the Fukushima Daiichi Nuclear Power Station accident in Japan, a multiple meteorological model and module ensemble analysis with a single chemical transport model (CTM) was conducted. Although several multimodel ensemble studies have previously been performed, the current type (i.e., one CTM with several meteorological fields) was applied for the first time and represents a useful way to evaluate the uncertainty of each component of CTM. The current analysis concluded that the underestimation of the deposition efficiency of CTM was the reason for the underestimation of simulated radio‐Cs deposition, whereas the simulated dispersion and precipitation and estimated source term were all reasonable: all of the simulations underestimated the deposition amount, whereas some underestimated but others overestimated the simulated precipitation and radio‐Cs concentrations. The CTM simulation performed using the meteorological ensemble mean field was successful in reducing variance, and they gave reasonable results. The simulated deposition using the meteorological ensemble was better than others because the ensemble mean enlarged the light precipitation areas and because the land contamination was mainly caused by light precipitation. The current ensemble study indicated that in‐cloud scavenging was the most dominant mechanism of radio‐Cs deposition, followed by dry deposition and fog deposition over the entire land area. In some deposition regions, fog deposition was dominant, exceeding 80%, depending on the simulations. The simulated concentrations and depositions varied by more than twofold, depending on the selection of the meteorological field. Key Points: Sensitivity to meteorological models was assessed for the first time for the Fukushima nuclear accident studyModeled deposition rates were underestimated, while precipitation values and source term were reasonableIn‐cloud scavenging was the most dominant mechanism for radio‐Cs deposition, followed by dry and fog depositions [ABSTRACT FROM AUTHOR]

The present study investigates the impact of tropical cyclone (TC) Nilam on the vertical distribution of carbon monoxide (CO) over Chennai in southern India. Measurements of OZone and water vapour by Airbus In‐service airCraft (MOZAIC) profiles of CO measured during October–November 2012 were analysed. The vertical profiles of CO on 15 October and 2 November were influenced by convective motions with a significant decrease in outgoing long‐wave radiation (OLR) compared to that on normal days of observations. The near‐surface mixing ratios of CO (185 ± 24 ppbv) in convectively influenced conditions were much lower than those measured during normal days (>210 ppbv). The occurrence of minimum CO values at altitudes of 4–6 km coincided with the lowest lapse rate (LR) value of 4–5 °C/km. The uplift of surface air masses led to a large increase in the CO mixing ratio in the free troposphere. The differences in CO between the lower and free troposphere were relatively small (40–50 ppbv) and large (90–100 ppbv) during convective and normal days, respectively. In the lower troposphere, elevated values of CO (>250 ppbv) were measured for lighter wind speeds from the north, while lower values (<150 ppbv) were measured for strong winds from the western sectors. The Model for OZone And Related chemical Tracers (MOZART‐4) and Chemistry Climate Model 2 (CCM2) simulations did not capture the detailed features of the CO profiles. For cyclone‐influenced measurements in the lower troposphere, MOZART‐4 underestimated the CO values by approximately 13%, but CCM2 overestimated the CO values by 70%. In the upper troposphere, MOZART‐4 and CCM2 underestimated the observations by 6–8% and 12–22%, respectively. The mixing scheme of the model and simulated concentrations seem to be the key causes of disagreements. However, the performances of both the MOZART‐4 and CCM2 simulations were better for convection‐free normal days. [ABSTRACT FROM AUTHOR]

The concentrations of atmospheric gases and aerosols were measured using the four-stage filter-pack method to study the atmospheric chemistry and the representativeness of a site established near an expressway and a national road with heavy traffic in a coastal as well as an urbanized area. The clear seasonal difference in the concentrations of nitrate species (HNO and NO ) between the two sites was observed, and the difference was correlated with, but not quantitative, the atmospheric oxidation reaction from NO to HNO. The concentrations of ammoniacal nitrogen (NH and NH ) were determined on a regional scale; in other words, their concentrations were not determined by specific emission sources, differently from the case of nitrate species. The temporal variation of the concentration of total sulfur (SO + SO ) was largely controlled by the concentration of SO, which, in turn, would be controlled by emission sources other than roads, differently from the cases of nitrate species and ammoniacal nitrogen. It was strongly suggested that there was an existence of the important sulfur emission sources: one candidate is sea traffic lane. [ABSTRACT FROM AUTHOR]

We estimated the inventories of radiocaesium released by the Tokyo Electric Power Company Fukushima Dai-ichi Nuclear Power Plant (FNPP1) accident to the North Pacific Ocean by using compiled data and model simulations. By comparing the observed inventories with model-simulated results, we obtained 12-15 PBq of Cs for the atmospheric deposition released by the FNPP1 accident in the North Pacific Ocean. Before the Fukushima accident, Cs activity in the North Pacific Ocean was about 69 PBq. Therefore, the 12-15 PBq of Cs newly added by atmospheric deposition together with the 3.5 ± 0.7 PBq added by direct discharge increased the total Cs inventory in the North Pacific Ocean by 22-27 %. We also estimated the total amount of Cs released to the atmosphere to be 15-20 PBq, and the total amount of Cs released to the environment to be 19-24 PBq, respectively. Observed Cs to Cs activity ratio at the time of accident was close to 1 and extremely uniform, therefore, the total amount of Cs deposition in the North Pacific Ocean, that of released to the atmosphere, that of direct discharge to the ocean and that of released to the environment were the same amounts as those of Cs. [ABSTRACT FROM AUTHOR]

In response to increasing trends in sulfur deposition in Northeast Asia, three countries in the region (China, Japan, and Korea) agreed to devise abatement strategies. The concepts of critical loads and source-receptor (S-R) relationships provide guidance for formulating such strategies. Based on the Long-range Transboundary Air Pollutants in Northeast Asia (LTP) project, this study analyzes sulfur deposition data in order to optimize acidic loads over the three countries. The three groups involved in this study carried out a full year (2002) of sulfur deposition modeling over the geographic region spanning the three countries, using three air quality models: MM5-CMAQ, MM5-RAQM, and RAMS-CADM, employed by Chinese, Japanese, and Korean modeling groups, respectively. Each model employed its own meteorological numerical model and model parameters. Only the emission rates for SO and NO obtained from the LTP project were the common parameter used in the three models. Three models revealed some bias from dry to wet deposition, particularly the latter because of the bias in annual precipitation. This finding points to the need for further sensitivity tests of the wet removal rates in association with underlying cloud-precipitation physics and parameterizations. Despite this bias, the annual total (dry plus wet) sulfur deposition predicted by the models were surprisingly very similar. The ensemble average annual total deposition was 7,203.6 ± 370 kt S with a minimal mean fractional error (MFE) of 8.95 ± 5.24 % and a pattern correlation (PC) of 0.89-0.93 between the models. This exercise revealed that despite rather poor error scores in comparison with observations, these consistent total deposition values across the three models, based on LTP group's input data assumptions, suggest a plausible S-R relationship that can be applied to the next task of designing cost-effective emission abatement strategies. [ABSTRACT FROM AUTHOR]

Recently, middle- and upper-atmosphere Doppler radar (MU radar) has enabled the measurement of middle-atmosphere turbulence from radar backscatter Doppler spectra. In this work, eddy diffusivities for momentum Km in the upper troposphere and lower stratosphere during clear-air conditions were derived from direct measurements of the Reynolds stress and vertical gradient of mean wind velocity measured by MU radar. Eddy diffusivity for heat Kh below 8 km was determined from measurements of temperature fluctuations by the Radio Acoustic Sounding System (RASS) attached to the MU radar. The eddy diffusivity for momentum was on the order of 10 m2 s−1 in the upper troposphere and decreased gradually in the stratosphere by an order of magnitude or more. The eddy diffusivity for heat was almost of the same order of magnitude as Km. Estimates of eddy diffusivity from the radar echo power spectral width give fairly good values compared with the direct measurement of Km. Applicability of three turbulence models-the spectral width method, the k-ℇε model modified for stratified flows, and the algebraic stress model-were also examined, using radar observation values of turbulent kinetic energy k and turbulent energy dissipation rate ℇε together with atmospheric stability observations from rawinsonde data. It is concluded that the algebraic stress model shows the best fit with the direct measurement of Km, even in the free atmosphere above the atmospheric boundary layer once k and ℇε values are obtained from observations or a model. [ABSTRACT FROM AUTHOR]

Three comprehensive acid deposition models were used to simulate the sulfur concentrations over northeast Asia over the period covering entire year of 2002, and discussed the aggregated uncertainties and discrepancies of the three models. The participating models are from the countries participating in the project of Longrange Transboundary Air Pollutants in Northeast Asia (LTP): China, Japan and Korea. The Eulerian Model-3/CMAQ (by China), Regional Air Quality Model (RAQM, by Japan), and Comprehensive Acid Deposition Model (CADM, by Korea) were employed by each country with common emissions data established by the administrative agencies of China, Japan and Korea. The episodic simulation results between 1 to 15, March 2002 are also presented, during which aircraft measurements were carried out over the Yellow sea. The episodic results show both a wide short-term variability in simulations against measurements, and maximum concentration differences of 3∼5 times among the three models, requiring that further attention before confidence among the three models can be claimed for short-term simulations. However, the year-long cumulative simulations showed almost the same general features, with lower aggregated uncertainties between the three models, produced by the long term integration over northeast Asia. [ABSTRACT FROM AUTHOR]

The algorithm used to retrieve the cloud effective particle radius from the 3.7 μm band was adapted to the corresponding channel of the Japanese Advanced Meteorological Imager (JAMI) flown on board the Multi-functional Transport Satellite (MTSAT) geostationary platform. Snapshot comparisons with spatially well-resolved retrievals from the MODerate resolution Imaging Spectrometer (MODIS) instruments flown on the Terra polar platforms show qualitative agreement with MTSAT retrievals. The results of analysing daytime variation from eastern Asia to the northwest Pacific Ocean show that, not only is the effective particle radius smaller in continental clouds than in maritime clouds, but the daytime amplitude of the effective particle radius is also greater in continental clouds than in maritime clouds, where the effective particle radius value is approximately constant. [ABSTRACT FROM AUTHOR]