Increase in tropospheric nitrogen dioxide over China observed from space

SO2-Induced Alkali Resistance of FeVO4/TiO2 Catalysts for NOx Reduction

Selective catalytic reduction of nitrogen oxides with ammonia (NH₃-SCR) is an efficient NO_x abatement strategy, but deNO_x catalysts suffer from serious deactivation due to the coexistence of multiple poisoning substances such as K, SO₂, etc. in the flue gas. It is essential to understand the interaction among various poisons and their effects on NO_x abatement. Here, we unexpectedly identified the K migration behavior induced by SO₂ over K-poisoned FeVO₄/TiO₂ catalysts, which led to alkali-poisoning buffering and activity recovery. It has been demonstrated that the K would occupy both redox and acidic sites, which severely reduced the reactivity of FeVO₄/TiO₂ catalysts. After the sulfuration of the K-poisoned catalyst, SO₂ preferred to be combined with the surface K₂O, lengthened the K-O_Fe and K-O_V, and thus released the active sites poisoned by K₂O, thereby preserving an increase in the activity. As a result, for the K-poisoned catalyst, the conversion of NO_x increased from 21 to 97% at 270 °C after the sulfuration process. This work contributes to the understanding of the specific interaction between alkali metals and SO₂ on deNO_x catalysts and provides a novel strategy for the adaptive use of one poisoning substance to counter another for practical NO_x reduction.

Insight on the anti-poisoning mechanism of in situ coupled sulfate over iron oxide catalysts in NOx reduction

In situ coupled sulfate uniquely migrated to the surface of iron oxide catalysts to capture metal poisons and thus maintained efficient adsorption and activation of NH3 and NOx reactants.

Spatio-temporal variations of tropospheric nitrogen dioxide in South Mato Grosso based on remote sensing by satellite

The study evaluates the characteristics of tropospheric nitrogen dioxide (NO2) concentrations from 2005 to 2020 in eight cities in the State of Mato Grosso do Sul (MS), Midwestern Brazil, using data available from the Ozone Monitoring Instrument (OMI). The average concentration varies from 2981 × 1015 molecules/cm2 in Campo Grande, where commercial, industrial and vehicular activities take place, to 2906 × 1015 molecules/cm2 in Corumbá and 3035 × 1015 molecules/cm2 in Porto Murtinho, regions of livestock and biomass burning. The results, based on the Mann–Kendall (MK) test, show a significant increase (p  < 0.05) in the NO2 column levels in the region. For each of the eight cities studied, a significant seasonal cycle of NO2 columns was determined. The maximum value of NO2 concentration was observed in the dry period, from July to September, while the minimum value was registered in the rainy period, from October to March.

Recent Advances in MnOx/CeO2-Based Ternary Composites for Selective Catalytic Reduction of NOx by NH3: A Review

Recently, manganese oxides (MnOx)/cerium(IV) oxide (CeO2) composites have attracted widespread attention for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) with ammonia (NH3), which exhibit outstanding catalytic performance owing to unique features, such as a large oxygen storage capacity, excellent low-temperature activity, and strong mechanical strength. The intimate contact between the components can effectively accelerate the charge transfer to enhance the electron–hole separation efficiency. Nevertheless, MnOx/CeO2 still reveals some deficiencies in the practical application process because of poor thermal stability, and a low reduction efficiency. Constructing MnOx/CeO2 with other semiconductors is the most effective strategy to further improve catalytic performance. In this article, we discuss progress in the field of MnOx/CeO2-based ternary composites with an emphasis on the SCR of NOx by NH3. Recent progress in their fabrication and application, including suitable examples from the relevant literature, are analyzed and summarized. In addition, the interaction mechanisms between MnOx/CeO2 catalysts and NOx pollutants are comprehensively dissected. Finally, the review provides basic insights into prospects and challenges for the advancement of MnOx/CeO2-based ternary catalysts.

Recent Breakthroughs and Advancements in NOx and SOx Reduction Using Nanomaterials-Based Technologies: A State-of-the-Art Review

Nitrogen and sulpher oxides (NO_x, SO_x) have become a global issue in recent years due to the fastest industrialization and urbanization. Numerous techniques are used to treat the harmful exhaust emissions, including dry, traditional wet and hybrid wet-scrubbing techniques. However, several difficulties, including high-energy requirement, limited scrubbing-liquid regeneration, formation of secondary pollutants and low efficiency, limit their industrial utilization. Regardless, the hybrid wet-scrubbing technology is gaining popularity due to low-costs, less-energy consumption and high-efficiency removal of air pollutants. The removal/reduction of NO_x and SO_x from the atmosphere has been the subject of several reviews in recent years. The goal of this review article is to help scientists grasp the fundamental ideas and requirements before using it commercially. This review paper emphasizes the use of green and electron-rich donors, new breakthroughs, reducing GHG emissions, and improved NO_x and SO_x removal catalytic systems, including selective/non-catalytic reduction (SCR/SNCR) and other techniques (functionalization by magnetic nanoparticles; NP, etc.,). It also explains that various wet-scrubbing techniques, synthesis of solid iron-oxide such as magnetic (Fe₃O₄) NP are receiving more interest from researchers due to the wide range of its application in numerous fields. In addition, EDTA coating on Fe₃O₄ NP is widely used due to its high stability over a wide pH range and solid catalytic systems. As a result, the Fe₃O₄@EDTA-Fe catalyst is projected to be an optimal catalyst in terms of stability, synergistic efficiency, and reusability. Finally, this review paper discusses the current of a heterogeneous catalytic system for environmental remedies and sustainable approaches.

A novel CNTs functionalized CeO2/CNTs-GAC catalyst with high NO conversion and SO2 tolerance for low temperature selective catalytic reduction of NO by NH3

Low-temperature selective catalytic reduction of NO_x by NH₃ (NH₃-SCR) for diminishing SO₂ poisoning remains an issue in flue gas denitrification (DeNO_x). Herein, A novel CNTs functionalized low temperature NH₃-SCR catalyst CeO₂/CNTs-GAC was prepared, which showed high NO conversion activity (100% at 150 °C) and SO₂ resistance. The addition of CNTs restrained SO₂ adsorption but improved the selective adsorption of NO, which restricted the deposition of (NH₄)₂SO₄ and/or Ce₂(SO₄)₃, and resulted in high SO₂ resistance. The addition of CNTs facilitated the diffusion and transportation of NH₃ and NO, and the electron transfer on CeO₂/CNTs-GAC, leading to higher content of Ce³⁺ and adsorbed O species on the CeO₂/CNTs-GAC surface and promoted formation of surface-adsorbed oxygen O_A. Therefore, CeO₂/CNTs-GAC provided abundant NO adsorption and activation sites, facilitating "fast SCR" reaction and enhancing the NH₃-SCR reaction. The proposed CeO₂/CNTs-GAC catalyst exhibited higher NH₃-SCR activity, N₂ selectivity, catalytic durability and SO₂ resistance than CeO₂/GAC.

Study on the Mechanism of SO2 Poisoning of MnOx/PG for Lower Temperature SCR by Simple Washing Regeneration

Manganese oxide-supported palygorskite (MnOx/PG) catalysts are considered highly efficient for low-temperature SCR of NOx. However, the MnOx/PG catalyst tends to be poisoned by SO2. The effect of SO2 on activity of the SO2-pretreated poisoning catalysts under ammonia-free conditions was explored. It was determined that the MnOx/PG catalyst tends to be considerably deactivated by SO2 in the absence of ammonia and that water-washed regeneration can completely recover activity of the deactivated catalyst. Based on these results and characterizations of the catalysts, a reasonable mechanism for the deactivation of MnOx/PG catalyst by SO2 was proposed in this study. SO2 easily oxidized to SO3 on the surface of the catalyst, leading to the formation of polysulfuric acid, wrapping of the active component and blocking the micropores. The deactivation of the MnOx/PG catalyst is initially caused by the formation of polysulfuric rather than the deposition of ammonia sulfate, which occurs later.

The Impact of Built and Social Environmental Characteristics on Diagnosed and Estimated Future Risk of Dementia

BACKGROUND

Dementia is a major global health challenge and the impact of built and social environments' characteristics on dementia risk have not yet been fully evaluated.

OBJECTIVE

To investigate associations between built and social environmental characteristics and diagnosed dementia cases and estimated dementia risk.

METHODS

We recruited 25,511 patients aged 65 and older from family physicians' practices. We calculated a dementia risk score based on risk and protective factors for patients not diagnosed with dementia. Our exposure variables were estimated for each statistical area level 1: social fragmentation, nitrogen dioxide, public open spaces, walkability, socio-economic status, and the length of main roads. We performed a multilevel mixed effect linear regression analysis to allow for the hierarchical nature of the data.

RESULTS

We found that a one standard deviation (1-SD) increase in NO2 and walkability score was associated with 10% higher odds of any versus no dementia (95% CI: 1%, 21% for NO2 and 0%, 22% for walkability score). For estimated future risk of dementia, a 1-SD increase in social fragmentation and NO2 was associated with a 1% increase in dementia risk (95% CI: 0, 1%). 1-SD increases in public open space and socioeconomic status were associated with 3% (95% CI: 0.95, 0.98) and 1% decreases (95% CI: 0.98, 0.99) in dementia risk, respectively. There was spatial heterogeneity in the pattern of diagnosed dementia and the estimated future risk of dementia.

CONCLUSION

Associations of neighborhood NO2 level, walkability, public open space, and social fragmentation with diagnosed dementia cases and estimated future risk of dementia were statistically significant, indicating the potential to reduce the risk through changes in built and social environments.

Alkali-Resistant Catalytic Reduction of NOx by Using Ce-O-B Alkali-Capture Sites

Reducing the poisoning effect arising from alkali metals over catalysts for selective catalytic reduction (SCR) of NO_x by NH₃ is still an urgent issue to be solved. Herein, alkali-resistant NO_x reduction over B-doped CeO₂/TiO₂ catalysts (Ce-B/TiO₂) with Ce-O-B alkali-capture sites was originally demonstrated. It was noted that boron was confirmed to be doped into the lattice of CeO₂ to form the Ce-O-B structure. In this way, more active Ce(III) species and oxygen vacancies were generated from B-doped CeO₂, thus accelerating the redox cycle and enhancing the adsorption/activation of NO. Gratifyingly, the created Ce-O-B sites as alkali-capture sites could be effectively combined with K and release the poisoned Ce active sites, which maintained efficient NH₃ and NO adsorption/activation over K poisoned Ce-B/TiO₂. This work paves a way for designing highly efficient and alkali-resistant SCR catalysts in both academic and industrial fields.

Nitrogen dioxide decline and rebound observed by GOME-2 and TROPOMI during COVID-19 pandemic

Since its first confirmed case in December 2019, coronavirus disease 2019 (COVID-19) has become a worldwide pandemic with more than 90 million confirmed cases by January 2021. Countries around the world have enforced lockdown measures to prevent the spread of the virus, introducing a temporal change of air pollutants such as nitrogen dioxide (NO2) that are strongly related to transportation, industry, and energy. In this study, NO2 variations over regions with strong responses to COVID-19 are analysed using datasets from the Global Ozone Monitoring Experiment-2 (GOME-2) sensor aboard the EUMETSAT Metop satellites and TROPOspheric Monitoring Instrument (TROPOMI) aboard the EU/ESA Sentinel-5 Precursor satellite. The global GOME-2 and TROPOMI NO2 datasets are generated at the German Aerospace Center (DLR) using harmonized retrieval algorithms; potential influences of the long-term trend and seasonal cycle, as well as the short-term meteorological variation, are taken into account statistically. We present the application of the GOME-2 data to analyze the lockdown-related NO2 variations for morning conditions. Consistent NO2 variations are observed for the GOME-2 measurements and the early afternoon TROPOMI data: regions with strong social responses to COVID-19 in Asia, Europe, North America, and South America show strong NO2 reductions of ∼ 30-50% on average due to restriction of social and economic activities, followed by a gradual rebound with lifted restriction measures.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11869-021-01046-2.

Alkali-Resistant Catalytic Reduction of NOx via Naturally Coupling Active and Poisoning Sites

Releasing the poisoning effect of alkali metals over catalysts is still an intractable issue for selective catalytic reduction (SCR) of NOx with ammonia. The presence of K in fly ash always dramatically suppressed catalytic activity by impairing acidity and redox properties, leading to severe reduction of lifetime for SCR catalysts. Herein, alkali-resistant NOx reduction over TiO2-supported Fe2(SO4)3 catalysts was originally demonstrated via naturally coupling active and poisoning sites. Notably, TiO2-supported Fe2(SO4)3 catalysts expressed admirable NOx conversion and K resistance within a quite broad temperature window of 200-500 °C. The catalysts with more conserved sulfate species revealed that sulfate groups preferred to migrate from the bulk phase to surface, thus effectively binding with K poisons to release the damage on iron active sites. Because of protection effects of migrated sulfates and closely coupling effects with Fe active sites, NH3 and NO adsorption amounts and rates were well maintained. In this way, Fe metal sites and sulfate species closely coupled together on a self-preserved TiO2-supported Fe2(SO4)3 catalyst played essential roles as highly active sites and unique poisoning sites. This work paves a new way to design SCR catalysts with superior alkali resistance that are more reliable in practical deNOx application.

Nanostructured Gas Sensors: From Air Quality and Environmental Monitoring to Healthcare and Medical Applications

In the last decades, nanomaterials have emerged as multifunctional building blocks for the development of next generation sensing technologies for a wide range of industrial sectors including the food industry, environment monitoring, public security, and agricultural production. The use of advanced nanosensing technologies, particularly nanostructured metal-oxide gas sensors, is a promising technique for monitoring low concentrations of gases in complex gas mixtures. However, their poor conductivity and lack of selectivity at room temperature are key barriers to their practical implementation in real world applications. Here, we provide a review of the fundamental mechanisms that have been successfully implemented for reducing the operating temperature of nanostructured materials for low and room temperature gas sensing. The latest advances in the design of efficient architecture for the fabrication of highly performing nanostructured gas sensing technologies for environmental and health monitoring is reviewed in detail. This review is concluded by summarizing achievements and standing challenges with the aim to provide directions for future research in the design and development of low and room temperature nanostructured gas sensing technologies.

Impacts of high-speed rail on urban smog pollution in China: A spatial difference-in-difference approach

Smog pollution poses a severe threat to residents' health and economic development in China. High-speed rail (HSR) is a new and efficient infrastructure that is expected to provide economic and environmental benefits. Based on the STIRPAT model and the environment Kuznets curve (EKC) hypothesis, this study employs a spatial difference-in-difference approach using 284 prefecture-level cities' panel data from 2007 to 2016 to explore the impacts of HSR on urban smog pollution. The results demonstrate that urban smog pollution shows strong spatial correlations and that HSR can significantly reduce smog pollution. Causal mediation analysis is used to test two mechanisms related to HSR: sector structure upgrading, which can reduce smog pollution, and real estate market development, which tends to increase smog pollution. After controlling for the two opposite mechanisms, HSR is proven to have positive environmental benefits. Besides HSR, the impacts of per capita GDP and population on smog pollution are further discussed. The relationship between per capita GDP and urban smog pollution follows an N-shaped curve, and smog is proved to reduce to a certain extent as per capita GDP increases. The relationship between population and smog pollution shows a U-shaped curve, provided with a new interpretation relating to economies of scale. The findings have implications for policy-making, as they enrich the EKC hypothesis and provide evidence for the environmental benefits of HSR.

Spatio-Temporal Variability of Aerosol Components, Their Optical and Microphysical Properties over North China during Winter Haze in 2012, as Derived from POLDER/PARASOL Satellite Observations

Pollution haze is a frequent phenomenon in the North China Plain (NCP) appearing during winter when the aerosol is affected by various pollutant sources and has complex distribution of the aerosol properties, while different aerosol components may have various critical effects on air quality, human health and radiative balance. Therefore, large-scale and accurate aerosol components characterization is urgently and highly desirable but hardly achievable at the regional scale. In this respect, directional and polarimetric remote sensing observations have great potential for providing information about the aerosol components. In this study, a state-of-the-art GRASP/Component approach was employed for attempting to characterize aerosol components in the NCP using POLDER/PARASOL satellite observations. The analysis was done for January 2012 in Beijing (BJ) and Shanxi (SX). The results indicate a peak of the BC mass concentration in an atmospheric column of 82.8 mg/m2 in the SX region, with a mean of 29.2 mg/m2 that is about four times higher than one in BJ (8.9 mg/m2). The mean BrC mass concentrations are, however, higher in BJ (up to ca. 271 mg/m2) than that in SX, which can be attributed to a higher anthropogenic emission. The mean amount of fine ammonium sulfate-like particles observed in the BJ region was three times lower than in SX (131 mg/m2). The study also analyzes meteorological and air quality data for characterizing the pollution event in BJ. During the haze episode, the results suggest a rapid increase in the fine mode aerosol volume concentration associated with a decrease of a scale height of aerosol down to 1500 m. As expected, the values of aerosol optical depth (AOD), absorbing aerosol optical depth (AAOD) and fine mode aerosol optical depth (AODf) are much higher on hazy days. The mass fraction of ammonium sulfate-like aerosol increases from about 13% to 29% and mass concentration increases from 300 mg/m2 to 500 mg/m2. The daily mean PM2.5 concentration and RH independently measured during these reported pollution episodes reach up to 425 g/m3 and 80% correspondingly. The monthly mean mass concentrations of other aerosol components in the BJ are found to be in agreement with the results of previous research works. Finally, a preliminary comparison of these remote sensing derived results with literature and in situ PM2.5 measurements is also presented.

Improved NOx Reduction over Phosphate-Modified Fe2O3/TiO2 Catalysts Via Tailoring Reaction Paths by In Situ Creating Alkali-Poisoning Sites

The deactivation issue arising from alkali poisoning over catalysts is still a challenge for the selective catalytic reduction of NO_x by NH₃. Herein, improved NO_x reduction in the presence of alkaline metals over phosphate-modified Fe₂O₃/TiO₂ catalysts has been originally demonstrated via tailoring the reaction paths by in situ creating alkali-poisoning sites. The introduction of phosphate results in the partial formation of iron phosphate species and makes the catalyst to mainly exhibit the characteristics of FePO₄, which is responsible for the widened temperature window and enhanced alkali resistance. The tetrahedral [FeO₄]/[PO₄] structures in iron phosphate act as the Brønsted acid sites to increase the catalyst surface acidity. In addition, the formation of an Fe-O-P structure enhances the redox ability and increases surface adsorbed oxygen. Furthermore, the created phosphate groups (PO₄^3-) serving as alkali-poisoning sites preferentially combine with potassium so that iron species on the active sites are protected. Therefore, the enhanced NH₃ species adsorption capacity, improved redox ability, and active nitrate species remaining in the phosphate-modified Fe₂O₃/TiO₂ catalyst ensure the de-NO_x activity after being poisoned by alkali metals through the Langmuir-Hinshelwood reaction pathway. Hopefully, this novel strategy could provide an inspiration to design novel catalysts to control NO_x emission with extraordinary resistance to alkaline metals.

Spatiotemporal changes in global nitrogen dioxide emission due to COVID-19 mitigation policies

This paper investigates spatiotemporal changes of nitrogen dioxide (NO₂) tropospheric vertical column density due to the COVID-19 pandemic using satellite observations before, during and after the lockdown (hereafter referred as the pre-, peri- and post-periods) in six different countries: China, South Africa, Brazil, India, the UK and the US, and compare these periods with 2019 as well as mean climatology from 2010 to 2019. We observe significant declines in relative differences (RDs) from the pre- to peri-period (as compared with the 10-year climatology) in most study countries including China, South Africa, India, and the UK by 15, 17, 8 and 7% respectively. The US does not demonstrate significant decline with RD difference relatively small at just 2%. Meanwhile, although the 2020 RD of Brazil is 7% lower than 2010–2019, this trend is quite similar to that of 2019 (20% vs 23%). In the post-period of 2020, the NO₂ columns rebound in most target countries: China, US, South Africa, Brazil and UK, with similar RDs relative to the corresponding pre-period as compared with 2019 and 2010–2019. In contrast, NO in India continues to be influenced by the ongoing COVID-19 crisis with pre-to-post RD 8% lower than the average of previous 10 years.

Ambient nitrogen dioxide and years of life lost from chronic obstructive pulmonary disease in the elderly: A multicity study in China

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is a leading cause of morbidity and mortality worldwide, and nitrogen dioxide (NO₂) is a potential environmental risk factor for COPD. However, association between ambient NO₂ and COPD risk remains underrecognized, especially in the elderly. This study aimed to explore association between NO₂ and years of life lost (YLL) from COPD in the elderly from 2013 to 2017 in 37 major cities in China.

METHODS

Ambient NO₂ data and COPD morality information were obtained from the National Urban Air Quality Real-time Publishing Platform and the Chinese Centers for Disease Control and Prevention, respectively. City-specific relative changes in YLL were estimated by generalized additive models, and meta-analysis was used to combine city-specific results. Potential modifications were evaluated. Economic loss due to excess YLL from COPD associated with ambient NO₂ was evaluated.

RESULTS

An increase of 10 μg/m³ in NO₂ for 2-day moving average led to 0.94% (95% CI: 0.56%, 1.31%) relative increase in COPD YLL. The associations were significantly higher in South than North China. Higher estimated effects were found in the warm than the cool season in the southern region. The relevant economic loss accounted for 0.04% (95% CI: 0.02%, 0.05%) of the gross domestic product (GDP) in China during the same period.

CONCLUSIONS

The findings provide evidence on the impact of short-term NO₂ exposure on COPD YLL in the elderly, which indicated more stringent control of NO₂ pollution and highlighted the need to protect the elderly during the warm season in South China.

Effects of urban functional fragmentation on nitrogen dioxide (NO2) variation with anthropogenic-emission restriction in China

Urban functional fragmentation plays an important role in assessing Nitrogen Dioxide (NO2) emissions and variations. While the mediated impact of anthropogenic-emission restriction has not been comprehensively discussed, the lockdown response to the novel coronavirus disease 2019 (COVID-19) provides an unprecedented opportunity to meet this goal. This study proposes a new idea to explore the effects of urban functional fragmentation on NO2 variation with anthropogenic-emission restriction in China. First, NO2 variations are quantified by an Autoregressive Integrated Moving Average with external variables-Dynamic Time Warping (SARIMAX-DTW)-based model. Then, urban functional fragmentation indices including industrial/public Edge Density (ED) and Landscape Shape Index (LSI), urban functional Aggregation Index (AI) and Number of Patches (NP) are developed. Finally, the mediated impacts of anthropogenic-emission restriction are assessed by evaluating the fragmentation-NO2 variation association before and during the lockdown during COVID-19. The findings reveal negative effects of industrial ED, public LSI, urban functional AI and NP and positive effects of public ED and industrial LSI on NO2 variation based on the restricted anthropogenic emissions. By comparing the association analysis before and during lockdown, the mediated impact of anthropogenic-emission restriction is revealed to partially increase the effect of industrial ED, industrial LSI, public LSI, urban functional AI and NP and decrease the effect of public ED on NO2 variation. This study provides scientific findings for redesigning the urban environment in related to the urban functional configuration to mitigating the air pollution, ultimately developing sustainable societies.

Superior Oxidative Dehydrogenation Performance toward NH3 Determines the Excellent Low-Temperature NH3-SCR Activity of Mn-Based Catalysts

Mn-based oxides exhibit outstanding low-temperature activity for the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) compared with other catalysts. However, the underlying principle responsible for the excellent low-temperature activity is not yet clear. Here, the atomic-level mechanism and activity-limiting factor in the NH₃-SCR process over Mn-, Fe-, and Ce-based oxide catalysts are elucidated by a combination of first-principles calculations and experimental measurements. We found that the superior oxidative dehydrogenation performance toward NH₃ of Mn-based catalysts reduces the energy barriers for the activation of NH₃ and the formation of the key intermediate NH₂NO, which is the rate-determining step in NH₃-SCR over these oxide catalysts. The findings of this study advance the understanding of the working principle of Mn-based SCR catalysts and provide a fundamental basis for the development of future generation SCR catalysts with excellent low-temperature activity.

The Korea-United States Air Quality (KORUS-AQ) field study

The Korea-United States Air Quality (KORUS-AQ) field study was conducted during May-June 2016. The effort was jointly sponsored by the National Institute of Environmental Research of South Korea and the National Aeronautics and Space Administration of the United States. KORUS-AQ offered an unprecedented, multi-perspective view of air quality conditions in South Korea by employing observations from three aircraft, an extensive ground-based network, and three ships along with an array of air quality forecast models. Information gathered during the study is contributing to an improved understanding of the factors controlling air quality in South Korea. The study also provided a valuable test bed for future air quality-observing strategies involving geostationary satellite instruments being launched by both countries to examine air quality throughout the day over Asia and North America. This article presents details on the KORUS-AQ observational assets, study execution, data products, and air quality conditions observed during the study. High-level findings from companion papers in this special issue are also summarized and discussed in relation to the factors controlling fine particle and ozone pollution, current emissions and source apportionment, and expectations for the role of satellite observations in the future. Resulting policy recommendations and advice regarding plans going forward are summarized. These results provide an important update to early feedback previously provided in a Rapid Science Synthesis Report produced for South Korean policy makers in 2017 and form the basis for the Final Science Synthesis Report delivered in 2020.

Identifying the driving factors of NO2 pollution of One Belt One Road countries: satellite observation technique and dynamic spatial panel data analysis

To recover the global economy, China in 2013 called for a new global strategy, namely, "One Belt and One Road Initiative" (BRI), which aims at reinforcing regional economic cooperation, enhancing regional collaboration of economic policy, and realizing the goal of rapid economic development of member countries. Accelerating industrialization not only has been recognized as an effective way to stimulate economic development, but also lead to the serious issue of environmental pollution, which challenges the environmental sustainability. In this study, we focus on the industrializing region as a study area to investigate the driving factors of environmental pollution. Technically, we utilized satellite observation technique to obtain NO₂ columns data to denote environmental pollution and then applied dynamic spatial panel data models to evaluate what affects NO₂ pollution levels. The findings are the following. (1) NO₂ pollution exhibits significant and positive spatial autocorrelation, indicating spatial spillovers of NO₂ pollution. (2) Lebanon, Bangladesh, Kyrgyzstan, and India experienced the largest increase of NO₂ pollution while NO₂ pollution in Singapore, Hungary, Greece, and Ukraine was substantially reduced. (3) The results of the dynamic spatial panel data models show that both the time dynamics effects and the spatial spillover effects are found to be significant and positive. In other words, both effects should be considered. Population is the foremost contributor to increase NO₂ pollution while urbanization is an effective way to reduce pollution. An EKC relationship between NO₂ pollution and per capita income was verified. Besides, industrialization, foreign direct investment, and trade openness have positive impacts on NO₂ pollution.

Estimation of nitrogen runoff loss from croplands in the Yangtze River Basin: A meta-analysis

Nitrogen (N) runoff loss from croplands due to excessive anthropogenic N additions is a principal cause of non-point source water pollution worldwide. Quantitative knowledge of regional-scale N runoff loss from croplands is essential for developing sustainable agricultural N management and efficient water N pollution control strategies. This meta-analysis quantifies N runoff loss rates and identifies the primary factors regulating N runoff loss from uplands (n = 570) and paddy (n = 434) fields in the Yangtze River Basin (YRB). Results indicated that total N (TN) runoff loss rates from uplands and paddy fields consistently increased from upstream to downstream regions. Runoff depth, soil N content and fertilizer addition rate (chemical fertilizer + manure) were the major factors regulating variability of TN runoff loss from uplands, while runoff depth and fertilizer addition rate were the main controls for paddy fields. Multiple regression models incorporating these influencing factors effectively predicted TN runoff loss rates from uplands (calibration: R² = 0.60, n = 242; validation: R² = 0.55, n = 104) and paddy fields (calibration: R² = 0.70, n = 189; validation: R² = 0.85, n = 82). Models estimated total cropland TN runoff loss load in YRB of 0.54 (95% Cl: 0.23-1.33) Tg, with 0.30 (95% Cl: 0.15-0.56) Tg from uplands and 0.24 (95% Cl: 0.08-0.77) Tg from paddy fields in 2017. Guangxi, Jiangxi, Fujian, Hunan and Henan provinces within the YRB were identified as cropland TN runoff loss hotspots. Models predicted that TN runoff loss loads from croplands in YRB would decrease by 0.8-13.7% for five scenarios, with higher TN load reductions occurring from scenarios with decreased runoff amounts. Reducing upland TN runoff loss should focus primarily on soil N utilization and runoff management, while reducing N fertilizer addition and runoff provided the most sensitive strategies for paddy fields. Integrated management of water, soil and fertilizer is required to effectively reduce cropland N runoff loss.

Derived habitats of indoor microbes are associated with asthma symptoms in Chinese university dormitories

Increasing evidence from the home environment indicates that indoor microbiome exposure is associated with asthma development. However, indoor microbiome composition can be highly diverse and dynamic, and thus current studies fail to produce consistent results. Chinese university dormitories are special high-density dwellings with similar building and occupants characteristics, which facilitate to disentangle the complex interactions between microbes, environmental characteristics and asthma. Settled air dust and floor dust was collected from 87 dormitory rooms in Shanxi University. Bacterial communities were characterized by 16 S rRNA amplicon sequencing. Students (n = 357) were surveyed for asthma symptoms and measured for fractional exhaled nitric oxide (FeNO). Asthma was not associated with the overall bacterial richness but associated with specific phylogenetic classes. Taxa richness and abundance in Clostridia, including Ruminococcus, Blautia, Clostridium and Subdoligranulum, were positively associated with asthma (p < 0.05), and these taxa were mainly derived from the human gut. Taxa richness in Alphaproteobacteria and Actinobacteria were marginally protectively associated with asthma, and these taxa were mainly derived from the outdoor environment. Bacterial richness and abundance were not associated with FeNO levels. Building age was associated with overall bacterial community variation in air and floor dust (p < 0.05), but not associated with the asthma-related microorganisms. Our data shows that taxa from different phylogenetic classes and derived habitats have different health effects, indicating the importance of incorporating phylogenetic and ecological concepts in revealing patterns in the microbiome asthma association analysis.

Reductions in NO2 burden over north equatorial Africa from decline in biomass burning in spite of growing fossil fuel use, 2005 to 2017

Socioeconomic development in low- and middle-income countries has been accompanied by increased emissions of air pollutants, such as nitrogen oxides [NO_x: nitrogen dioxide (NO₂) + nitric oxide (NO)], which affect human health. In sub-Saharan Africa, fossil fuel combustion has nearly doubled since 2000. At the same time, landscape biomass burning-another important NO_x source-has declined in north equatorial Africa, attributed to changes in climate and anthropogenic fire management. Here, we use satellite observations of tropospheric NO₂ vertical column densities (VCDs) and burned area to identify NO₂ trends and drivers over Africa. Across the northern ecosystems where biomass burning occurs-home to hundreds of millions of people-mean annual tropospheric NO₂ VCDs decreased by 4.5% from 2005 through 2017 during the dry season of November through February. Reductions in burned area explained the majority of variation in NO₂ VCDs, though changes in fossil fuel emissions also explained some variation. Over Africa's biomass burning regions, raising mean GDP density (USD⋅km^-2) above its lowest levels is associated with lower NO₂ VCDs during the dry season, suggesting that economic development mitigates net NO₂ emissions during these highly polluted months. In contrast to the traditional notion that socioeconomic development increases air pollutant concentrations in low- and middle-income nations, our results suggest that countries in Africa's northern biomass-burning region are following a different pathway during the fire season, resulting in potential air quality benefits. However, these benefits may be lost with increasing fossil fuel use and are absent during the rainy season.

Impact of the COVID-19 outbreak on air pollution levels in East Asia

This study leverages satellite remote sensing to investigate the impact of the coronavirus outbreak and the resulting lockdown of public venues on air pollution levels in East Asia. We analyze data from the Sentinel-5P and the Himawari-8 satellites to examine concentrations of NO₂, HCHO, SO₂, and CO, and the aerosol optical depth (AOD) over the BTH, Wuhan, Seoul, and Tokyo regions in February 2019 and February 2020. Results show that most of the concentrations of pollutants are lower than those of February 2019. Compared to other pollutants, NO₂ experienced the most significant reductions by almost 54%, 83%, 33%, and 19% decrease in BTH, Wuhan, Seoul, and Tokyo, respectively. The greatest reductions in pollutants occurred in Wuhan, with a decrease of almost 83%, 11%, 71%, and 4% in the column densities of NO₂, HCHO, SO₂, and CO, respectively, and a decrease of about 62% in the AOD. Although NO₂, CO, and formaldehyde concentrations decreased in the Seoul and Tokyo metropolitan areas compared to the previous year, concentrations of SO₂ showed an increase in these two regions due to the effect of transport from polluted upwind regions. We also show that meteorological factors were not the main reason for the dramatic reductions of pollutants in the atmosphere. Moreover, an investigation of the HCHO/NO₂ ratio shows that in many regions of East China, particularly in Wuhan, ozone production in February 2020 is less NO_X saturated during the daytime than it was in February 2019. With large reductions in the concentrations of NO₂ during lockdown situations, we find that significant increases in surface ozone in East China from February 2019 to February 2020 are likely the result of less reaction of NO and O₃ caused by significantly reduced NO_X concentrations and less NO_X saturation in East China during the daytime.

Ground-Based MAX-DOAS Observations of Tropospheric NO2 and HCHO During COVID-19 Lockdown and Spring Festival Over Shanghai, China

Reduced mobility and less anthropogenic activity under special case circumstances over various parts of the world have pronounced effects on air quality. The objective of this study is to investigate the impact of reduced anthropogenic activity on air quality in the mega city of Shanghai, China. Observations from the highly sophisticated multi-axis differential optical absorption spectroscope (MAX-DOAS) instrument were used for nitrogen dioxide (NO2) and formaldehyde (HCHO) column densities. In situ measurements for NO2, ozone (O3), particulate matter (PM2.5) and the air quality index (AQI) were also used. The concentration of trace gases in the atmosphere reduces significantly during annual Spring Festival holidays, whereby mobility is reduced and anthropogenic activities come to a halt. The COVID-19 lockdown during 2020 resulted in a considerable drop in vertical column densities (VCDs) of HCHO and NO2 during lockdown Level-1, which refers to strict lockdown, i.e., strict measures taken to reduce mobility (43% for NO2; 24% for HCHO), and lockdown Level-2, which refers to relaxed lockdown, i.e., when the mobility restrictions were relaxed somehow (20% for NO2; 22% for HCHO), compared with pre-lockdown days, as measured by the MAX-DOAS instrument. However, for 2019, a reduction in VCDs was found only during Level-1 (24% for NO2; 6.62% for HCHO), when the Spring Festival happened. The weekly cycle for NO2 and HCHO depicts no significant effect of weekends on the lockdown. After the start of the Spring Festival, the VCDs of NO2 and HCHO showed a decline for 2019 as well as 2020. Backward trajectories calculated using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model indicated more air masses coming from the sea after the Spring Festival for 2019 and 2020, implying that a low pollutant load was carried by them. No impact of anthropogenic activity was found on O3 concentration. The results indicate that the ratio of HCHO to NO2 (RFN) fell in the volatile organic compound (VOC)-limited regime.

Important contributions of non-fossil fuel nitrogen oxides emissions

Since the industrial revolution, it has been assumed that fossil-fuel combustions dominate increasing nitrogen oxide (NO_x) emissions. However, it remains uncertain to the actual contribution of the non-fossil fuel NO_x to total NO_x emissions. Natural N isotopes of NO₃⁻ in precipitation (δ¹⁵N_w-NO3−) have been widely employed for tracing atmospheric NO_x sources. Here, we compiled global δ¹⁵N_w-NO3− observations to evaluate the relative importance of fossil and non-fossil fuel NO_x emissions. We found that regional differences in human activities directly influenced spatial-temporal patterns of δ¹⁵N_w-NO3− variations. Further, isotope mass-balance and bottom-up calculations suggest that the non-fossil fuel NO_x accounts for 55 ± 7% of total NO_x emissions, reaching up to 21.6 ± 16.6Mt yr⁻¹ in East Asia, 7.4 ± 5.5Mt yr⁻¹ in Europe, and 21.8 ± 18.5Mt yr⁻¹ in North America, respectively. These results reveal the importance of non-fossil fuel NO_x emissions and provide direct evidence for making strategies on mitigating atmospheric NO_x pollution.

This study investigates in the importance of non-fossil fuel NO_x emissions in the surface-earth-nitrogen cycle. The study shows how changes of regional human activities directly influence δ¹⁵N signatures of deposited NO_x to terrestrial environments and that emissions have largely been underestimated.

Tailored activity of Cu–Fe bimetallic Beta zeolite with promising C3H6 resistance for NH3-SCR

The introduction of Cu has inhibited the polymerization of C₃H₆ and promoted the oxidation of C₃H₆, which alleviated competitive adsorption between C₃H₆ and NO_x, therefore results in the enhanced NH₃-SCR performance in the presence of C₃H₆.

Strategy and Future Prospects to Develop Room-Temperature-Recoverable NO2 Gas Sensor Based on Two-Dimensional Molybdenum Disulfide

Nitrogen dioxide (NO2), a hazardous gas with acidic nature, is continuously being liberated in the atmosphere due to human activity. The NO2 sensors based on traditional materials have limitations of high-temperature requirements, slow recovery, and performance degradation under harsh environmental conditions. These limitations of traditional materials are forcing the scientific community to discover future alternative NO2 sensitive materials. Molybdenum disulfide (MoS2) has emerged as a potential candidate for developing next-generation NO2 gas sensors. MoS2 has a large surface area for NO2 molecules adsorption with controllable morphologies, facile integration with other materials and compatibility with internet of things (IoT) devices. The aim of this review is to provide a detailed overview of the fabrication of MoS2 chemiresistance sensors in terms of devices (resistor and transistor), layer thickness, morphology control, defect tailoring, heterostructure, metal nanoparticle doping, and through light illumination. Moreover, the experimental and theoretical aspects used in designing MoS2-based NO2 sensors are also discussed extensively. Finally, the review concludes the challenges and future perspectives to further enhance the gas-sensing performance of MoS2. Understanding and addressing these issues are expected to yield the development of highly reliable and industry standard chemiresistance NO2 gas sensors for environmental monitoring.

COVID-19 and the Improvement of the Global Air Quality: The Bright Side of a Pandemic

The objective of this investigation is to study the impacts of the global response to COVID-19 on air pollution and air quality changes in major cities across the globe over the past few months. Air quality data (NO2, CO, PM2.5, and O3) were downloaded from the World Air Quality Index project for the January 2019–April 2020 period. Results show a significant reduction in the levels of 2020 NO2, CO, and PM2.5 compared to their levels in 2019. These reductions were as high as 63% (Wuhan, China), 61% (Lima, Peru), and 61% (Berlin, Germany), in NO2, CO, and PM2.5 levels, respectively. In contrast, 2020 O3 levels increased substantially, as high as 86% (Milan, Italy), in an apparent response to the decrease in titration by nitrogen monoxide and its derivatives. Significant differences in the weather conditions across the globe do not seem to impact this air quality improvement trend. Will this trend in the reduction in most air pollutants to unprecedented levels continue in the next few weeks or even months? The response to this and other questions will depend on the future global economic and environmental policies.

Non-negligible impacts of clean air regulations on the reduction of tropospheric NO2 over East China during the COVID-19 pandemic observed by OMI and TROPOMI

We study the variation of tropospheric NO₂ vertical column densities (TropNO₂VCDs) over East China during the 2005-2020 lunar new year (LNY) holiday seasons to understand factors on the reduction of tropospheric NO₂ during the outbreak of COVID-19 in East China using Ozone Monitoring Instrument (OMI) and TROPOspheric Monitoring Instrument (TROPOMI) observations. TropNO₂VCDs from OMI and TROPOMI reveal sharp reductions of 33%-72% during 2020 LNY holiday season and the co-occurring outbreak of COVID-19 relative to the climatological mean of 2005-2019 LNY holiday seasons, and 22%-67% reduction relative to the 2019 LNY holiday season. These reductions of TropNO₂VCD occur majorly over highly polluted metropolitan areas with condensed industrial and transportation emission sources. COVID-19 control measures including lockdowns and shelter-in-place regulations are the primary reason for these tropospheric NO₂ reductions over most areas of East China in 2020 LNY holiday season relative to the 2019 LNY holiday season, as COVID-19 control measures may explain ~87%-90% of tropospheric NO₂ reduction in Wuhan as well as ~62%-89% in Beijing, Yangtze River Delta (YRD) and Sichuan Basin areas. The clean air regulation of China also contributes significantly to reductions of tropospheric NO₂ simultaneously and is the primary factor in the Pearl River Delta (PRD) area, by explaining ~56%-63% of the tropospheric NO₂ reduction there.

Unveiling the Remarkable Arsenic Resistance Origin of Alumina Promoted Cerium-Tungsten Catalysts for NH3-SCR

The deactivation of selective catalytic reduction (SCR) catalysts by arsenic is a serious problem for NH₃-SCR. However, it is tough to design catalysts with good resistance to arsenic compared to other poisons such as alkali metal, SO₂, etc., because As not only deteriorates surface acidity but also redox property, causing excessive N₂O generation. A novel CeO₂-WO₃-Al₂O₃ catalyst is developed with excellent arsenic resistance in this study, which presents only less than 10% activity loss compared to nearly 40% loss for CeO₂-WO₃ with same arsenic loading (As: 2.1 wt %). Moreover, a significant negative impact on the N₂O generation for poisoning catalysts from 26.7 to 7.5 ppm has also been found. The characterization results demonstrated that the interaction between cerium and arsenic lead to Lewis acid sites and oxygen vacancies loss as well as unexpected oxidation sites formation. However, the introduction of Al weakens the deactivation effect by replacing cerium to interact with arsenic. Three aspects are proposed for obtaining excellent arsenic-resistant performance: (1) the protection of Lewis acid sites, (2) release of oxygen vacancies from As restriction, and (3) confinement of As⁵⁺ oxidizing capacity. This study may provide an effective strategy to design and develop novel virtuous antipoisoning catalysts.

Investigation of Water and Sulfur Tolerance of Precipitable Silver Compound Ag/Al2O3 Catalysts in H2-Assisted C3H6-SCR of NOx

Ag/Al₂O₃ catalysts containing different precipitable silver compounds (AgCl, Ag₂SO₄, and Ag₃PO₄) were synthesized and investigated for NOx reduction in H₂-assisted C₃H₆-selective catalytic reduction (SCR). The samples were systematically characterized by N₂ adsorption, X-ray diffraction (XRD), UV-Vis, X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HR-TEM). N₂ adsorption revealed that the introduction of anions (Cl^-, SO₄ ^2-, and PO₄ ^3-) did not significantly affect the surface and structural properties of the Al₂O₃ support. However, XRD patterns and HR-TEM images indicated that the addition of Cl^- anions caused the agglomeration of silver species to form large AgCl particles on the AgCl/Al₂O₃ catalysts. In contrast, the silver species dispersed well on Ag₂SO₄/Al₂O₃ and Ag₃PO₄/Al₂O₃ catalysts. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed that partial oxidation of C₃H₆ on Ag₂SO₄/Al₂O₃ produced large amounts of reactive enolic species, while it tended to yield inert formate on AgCl/Al₂O₃. As a result, Ag₂SO₄/Al₂O₃ catalysts, especially 3% Ag₂SO₄/Al₂O₃, exhibited superior water and sulfur tolerance in H₂-assisted C₃H₆-SCR.

Environmental impacts of nitrogen emissions in China and the role of policies in emission reduction

Atmospheric reactive nitrogen (N_r) has been a cause of serious environmental pollution in China. Historically, China used too little N_r in its agriculture to feed its population. However, with the rapid increase in N fertilizer use for food production and fossil fuel consumption for energy supply over the last four decades, increasing gaseous N_r species (e.g. NH₃ and NO_x) have been emitted to the atmosphere and then deposited as wet and dry deposition, with adverse impacts on air, water and soil quality as well as plant biodiversity and human health. This paper reviews the issues associated with this in a holistic way. The emissions, deposition, impacts, actions and regulations for the mitigation of atmospheric N_r are discussed systematically. Both NH₃ and NO_x make major contributions to environmental pollution but especially to the formation of secondary fine particulate matter (PM_2.5), which impacts human health and light scattering (haze). In addition, atmospheric deposition of NH₃ and NO_x causes adverse impacts on terrestrial and aquatic ecosystems due to acidification and eutrophication. Regulations and practices introduced by China that meet the urgent need to reduce N_r emissions are explained and resulting effects on emissions are discussed. Recommendations for improving future N management for achieving 'win-win' outcomes for Chinese agricultural production and food supply, and human and environmental health, are described. This article is part of a discussion meeting issue 'Air quality, past present and future'.

A chronology of global air quality

Air pollution has been recognized as a threat to human health since the time of Hippocrates, ca 400 BC. Successive written accounts of air pollution occur in different countries through the following two millennia until measurements, from the eighteenth century onwards, show the growing scale of poor air quality in urban centres and close to industry, and the chemical characteristics of the gases and particulate matter. The industrial revolution accelerated both the magnitude of emissions of the primary pollutants and the geographical spread of contributing countries as highly polluted cities became the defining issue, culminating with the great smog of London in 1952. Europe and North America dominated emissions and suffered the majority of adverse effects until the latter decades of the twentieth century, by which time the transboundary issues of acid rain, forest decline and ground-level ozone became the main environmental and political air quality issues. As controls on emissions of sulfur and nitrogen oxides (SO₂ and NO_x) began to take effect in Europe and North America, emissions in East and South Asia grew strongly and dominated global emissions by the early years of the twenty-first century. The effects of air quality on human health had also returned to the top of the priorities by 2000 as new epidemiological evidence emerged. By this time, extensive networks of surface measurements and satellite remote sensing provided global measurements of both primary and secondary pollutants. Global emissions of SO₂ and NO_x peaked, respectively, in ca 1990 and 2018 and have since declined to 2020 as a result of widespread emission controls. By contrast, with a lack of actions to abate ammonia, global emissions have continued to grow. This article is part of a discussion meeting issue 'Air quality, past present and future'.

Years of life lost from ischaemic and haemorrhagic stroke related to ambient nitrogen dioxide exposure: A multicity study in China

Few multicity studies have been conducted in developing countries to distinguish the acute effects of ambient nitrogen dioxide (NO₂) on the years of life lost (YLL) from different subtypes of stroke. We aimed to differentiate the associations between NO₂ exposure and YLL from major pathological types of stroke in China, and estimate the relevant economic loss. A time-series study was conducted to explore the associations between short-term NO₂ exposure and YLL from ischaemic and haemorrhagic stroke from 2013 to 2017 in 48 Chinese cities. Daily NO₂ data and stroke mortality counts for each city were obtained from the National Urban Air Quality Real-time Publishing Platform and Chinese Center for Disease Control and Prevention, respectively. Generalized additive models were applied to estimate the cumulative effects of NO₂ in each city, and meta-analysis was used to combine the city-specific estimates. The relevant economic loss was estimated using the method of the value per statistical life year (VSLY). A 10 μg/m³ increase in ambient NO₂ concentration on the present day and previous day (lag 0-1) would lead to relatively higher increments in percentage change of YLL from ischaemic stroke (0.82%, 95% CI: 0.46%, 1.19%) than haemorrhagic stroke (0.46%, 95% CI: 0.09%, 0.84%). The association was significantly stronger in the low-education population than high-education population for ischaemic stroke. Furthermore, significantly higher association was found in South China than those in North China for both subtypes of stroke. Economic loss due to excess YLL from ischaemic stroke related to NO₂ exposure was higher than that for haemorrhagic stroke. Our study indicated higher association and economic loss of ischaemic than haemorrhagic stroke related to NO₂ exposure in China, which informed priorities for type-specific stroke prevention strategies related to NO₂ pollution and vulnerable population protection.

Self-Protected CeO2-SnO2@SO42-/TiO2 Catalysts with Extraordinary Resistance to Alkali and Heavy Metals for NOx Reduction

Reducing the poisoning effect of alkali and heavy metals over ammonia selective catalytic reduction (NH₃-SCR) catalysts is still an intractable issue, as the presence of K and Pb in fly ash greatly hampers their catalytic activity by impairing the acidity and affecting the redox properties of the catalysts, leading to the reduction in the lifetime of SCR catalysts. To address this issue, we propose a novel self-protected antipoisoning mechanism by designing SO₄^2-/TiO₂ superacid supported CeO₂-SnO₂ catalysts. Owing to the synergistic effect between CeO₂ and SnO₂ and the strong acidity originating from the SO₄^2-/TiO₂ superacid, the catalysts show superior catalytic activity over a wide temperature range (240-510 °C). Moreover, when K or/and Pb are deposited on SO₄^2-/TiO₂ catalysts, the bond effect between SO₄^2- and Ti-O would be broken so that the sulfate in the bulk of SO₄^2-/TiO₂ superacid support would be induced to migrate to the surface to bond with K and Pb, thus prohibiting poisons from attacking the Ce-Sn active sites, and significantly boosting the resistance. Hopefully, this novel self-protection mechanism derived from the migration of sulfate in the SO₄^2-/TiO₂ superacid to resist alkali and heavy metals provides a new avenue for designing novel catalysts with outstanding resistance to alkali and heavy metals.

Modeling the Contribution of Crops to Nitrogen Pollution in the Yangtze River

Agriculture contributes considerably to nitrogen (N) inputs to the world's rivers. In this study, we aim to improve our understanding of the contribution of different crops to N inputs to rivers. To this end, we developed a new model system by linking the MARINA 2.0 (Model to Assess River Input of Nutrient to seAs) and WOFOST (WOrld FOod STudy) models. We applied this linked model system to the Yangtze as an illustrative example. The N inputs to crops in the Yangtze River basin showed large spatial variability. Our results indicate that approximately 6,000 Gg of N entered all rivers of the Yangtze basin from crop production as dissolved inorganic N (DIN) in 2012. Half of this amount is from the production of single rice, wheat, and vegetables, where synthetic fertilizers were largely applied. In general, animal manure contributes 12% to total DIN inputs to rivers. Three-quarters of manure-related DIN in rivers are from vegetable, fruit, and potato production. The contributions of crops to river pollution differ among sub-basins. For example, potato is an important source of DIN in rivers of some upstream sub-basins. Our results may help to prioritize the dominant crop sources for management to mitigate N pollution in the future.

Ground-based and OMI-TROPOMI NO2 measurements at El Arenosillo observatory: Unexpected upward trends

Eleven years, January 2008 to June 2019, of hourly nitrogen dioxide (NO₂) levels recorded at El Arenosillo observatory (Southwestern Europe) were analyzed. Annual averages ranged between 4 μg m^-3 and 6 μg m^-3 with peaks exceeding 40 μg m^-3. A slight monthly variation was observed with maximum and minimum values in the cold (∼6 μg m^-3) and warm (∼4 μg m^-3) seasons respectively. A diurnal pattern was found with a weak amplitude (∼3 μg m^-3). The monthly trends were investigated using surface observations and OMI (Ozone Monitoring instrument) satellite measurements. An unexpected upward trend was obtained in the last five years. The periods with elevated NO₂ concentrations in the last years were analyzed, showing an increase in its frequency and concentrations, linked with the upward trend observed. The weather conditions in these NO₂ peaks were studied using local surface meteorology, mean sea level pressure and wind fields from the data reanalysis of ERA5. The transport of NO₂ was explored using TROPOMI (Tropospheric Monitoring Instrument) measurements. The events occurred under conditions governed by high-pressure systems, which induced weak synoptic airflows or the development of mesoscale processes. Four scenarios of NO₂ transport were identified, associated with weak synoptic flows from inland or Southern Portugal and with mesoscale processes. The gulf of Cadiz plays an important role as a reservoir where the NO₂ coming from the south of Portugal, the Western Mediterranean Basin and urban-industrial areas can be accumulated and later transported inland. A strong correlation was found between the increase of NO₂ observed in the last years and positive anomalies of the temperature and geopotential height at 850 and 500 hPa levels. These findings could indicate that the causes of the changes in the NO₂ would be attributed to alterations in the weather patterns associated with a warmer climate.

Remote Sensing Estimation of Regional NO2 via Space-Time Neural Networks

Nitrogen dioxide (NO2) is an essential air pollutant related to adverse health effects. A space-time neural network model is developed for the estimation of ground-level NO2 in this study by integrating ground NO2 station measurements, satellite NO2 products, simulation data, and other auxiliary data. Specifically, a geographically and temporally weighted generalized regression neural network (GTW-GRNN) model is used with the advantage to consider the spatiotemporal variations of the relationship between NO2 and influencing factors in a nonlinear neural network framework. The case study across the Wuhan urban agglomeration (WUA), China, indicates that the GTW-GRNN model outperforms the widely used geographically and temporally weighted regression (GTWR), with the site-based cross-validation R2 value increasing by 0.08 (from 0.61 to 0.69). Besides, the comparison between the GTW-GRNN and original global GRNN models shows that considering the spatiotemporal variations in GRNN modeling can boost estimation accuracy. All these results demonstrate that the GTW-GRNN based NO2 estimation framework will be of great use for remote sensing of ground-level NO2 concentrations.

The contributions of socioeconomic and natural factors to the acid deposition over China

China has experienced severe acid rain pollution during the past decades due to excessive sulfur oxides (SO₂) and nitrous oxides (NO_x) emissions, which further caused lake acidification, biodiversity losses and climate change. Although the major sources of acid deposition have been clarified previously, the contributions of socioeconomic (natural) factors to the regional acid deposition remained unknown. Therefore, a series of valuable data including socioeconomic (natural) variables and measured pH value in the rainwater at the city level were collected to identify the key factors influencing the rainwater pH value at the national and the regional scale using the spatial econometric model/geographical detector technique and geographical weight regression (GWR) model, respectively. The results showed that the annual mean pH value in the rainwater in China was 6.54 ± 0.72. The rainwater pH in winter (6.01 ± 0.41) was significantly lower than those observed during summer (6.74 ± 0.64), spring (6.71 ± 0.71) and autumn (6.71 ± 0.69). The spatial econometric model indicated that socioeconomic indicators including per capita gross industrial production (GIP), ratio of built-up area to the urban land (RBU), foreign direct investment (FDI), SO₂ emission, and meteorological factors of annual mean precipitation (AMP), and annual mean relative humidity (AMRH) were the main factors for the acid deposition. The geographical detector technique implied that the power of determinants were in the order of AMRH (10.00%) = AMP (10.00%) > SO₂ emission (8.51%) > FDI (8.32%) > RBU (7.64%) > per capita GIP (7.00%). The GWR implied that GIP, FDI, and SO₂ emission made relatively higher contribution to acid deposition in East China relative to other regions owning to the huge population and the higher energy consumption. The higher rainfall amount and RH in Southeast China significantly increased the pollutant deposition fluxes and promoted the heterogeneous transformations of precursors of acid rain, respectively. The findings herein shed light upon the socioeconomic forces for the acid deposition in China for the first time and provided the new information for government sectors to control the acid rain pollution in the future.

Hybrid Deep Learning Algorithm with Open Innovation Perspective: A Prediction Model of Asthmatic Occurrence

Due to recent advancements in industrialization, climate change and overpopulation, air pollution has become an issue of global concern and air quality is being highlighted as a social issue. Public interest and concern over respiratory health are increasing in terms of a high reliability of a healthy life or the social sustainability of human beings. Air pollution can have various adverse or deleterious effects on human health. Respiratory diseases such as asthma, the subject of this study, are especially regarded as ‘directly affected’ by air pollution. Since such pollution is derived from the combined effects of atmospheric pollutants and meteorological environmental factors, and it is not easy to estimate its influence on feasible respiratory diseases in various atmospheric environments. Previous studies have used clinical and cohort data based on relatively a small number of samples to determine how atmospheric pollutants affect diseases such as asthma. This has significant limitations in that each sample of the collections is likely to produce inconsistent results and it is difficult to attempt the experiments and studies other than by those in the medical profession. This study mainly focuses on predicting the actual asthmatic occurrence while utilizing and analyzing the data on both the atmospheric and meteorological environment officially released by the government. We used one of the advanced analytic models, often referred to as the vector autoregressive model (VAR), which traditionally has an advantage in multivariate time-series analysis to verify that each variable has a significant causal effect on the asthmatic occurrence. Next, the VAR model was applied to a deep learning algorithm to find a prediction model optimized for the prediction of asthmatic occurrence. The average error rate of the hybrid deep neural network (DNN) model was numerically verified to be about 8.17%, indicating better performance than other time-series algorithms. The proposed model can help streamline the national health and medical insurance system and health budget management in South Korea much more effectively. It can also provide efficiency in the deployment and management of the supply and demand of medical personnel in hospitals. In addition, it can contribute to the promotion of national health, enabling advance alerts of the risk of outbreaks by the atmospheric environment for chronic asthma patients. Furthermore, the theoretical methodologies, experimental results and implications of this study will be able to contribute to our current issues of global change and development in that the meteorological and environmental data-driven, deep-learning prediction model proposed hereby would put forward a macroscopic directionality which leads to sustainable public health and sustainability science.

N-Doped Graphene Quantum Dot-Decorated Three-Dimensional Ordered Macroporous In2O3 for NO2 Sensing at Low Temperatures

Nitrogen dioxide (NO₂) detection is of great importance because the emission of NO₂ gas profoundly endangers the natural environment and human health. However, a few challenges, including lowering detection limit, improving response/recovery kinetics, and reducing working temperature, should be further addressed before practical applications. Herein, a series of N-doped graphene quantum dot (N-GQD)-modified three-dimensional ordered macroporous (3DOM) In₂O₃ composites are constructed and their NO₂ response properties are studied. The results show that compared to pure 3DOM In₂O₃, reduced graphene oxide (rGO)/3DOM In₂O₃, and N-doped graphene sheets (NS)/3DOM In₂O₃, the N-GQDs/3DOM In₂O₃ sensing materials exhibit higher NO₂ responses with fast response and recovery speed and low working temperature (100 °C). In addition, the detection limit of NO₂ response for the optimal N-GQDs/In₂O₃ sensor is as low as 100 ppb. Upon exposure to CO, CH₄, NH₃, acetone, ethanol, toluene, and formaldehyde, only very weak responses could be observed, indicating good selectivity for the synthesized material. More attractively, the responses of the optimized N-GQDs/In₂O₃ sensor exhibit no obviously big fluctuation over 60 days, implying good long-term stability. We suggest that the formation of heterojunctions between 3DOM In₂O₃ and N-GQDs and the doping N atoms in N-GQDs play crucial roles in improving the NO₂ sensing properties.

Severe air pollution events not avoided by reduced anthropogenic activities during COVID-19 outbreak

Due to the pandemic of coronavirus disease 2019 in China, almost all avoidable activities in China are prohibited since Wuhan announced lockdown on January 23, 2020. With reduced activities, severe air pollution events still occurred in the North China Plain, causing discussions regarding why severe air pollution was not avoided. The Community Multi-scale Air Quality model was applied during January 01 to February 12, 2020 to study PM_2.5 changes under emission reduction scenarios. The estimated emission reduction case (Case 3) better reproduced PM_2.5. Compared with the case without emission change (Case 1), Case 3 predicted that PM_2.5 concentrations decreased by up to 20% with absolute decreases of 5.35, 6.37, 9.23, 10.25, 10.30, 12.14, 12.75, 14.41, 18.00 and 30.79 μg/m³ in Guangzhou, Shanghai, Beijing, Shijiazhuang, Tianjin, Jinan, Taiyuan, Xi'an, Zhengzhou, Wuhan, respectively. In high-pollution days with PM_2.5 greater than 75 μg/m³, the reductions of PM_2.5 in Case 3 were 7.78, 9.51, 11.38, 13.42, 13.64, 14.15, 14.42, 16.95 and 22.08 μg/m³ in Shanghai, Jinan, Shijiazhuang, Beijing, Taiyuan, Xi'an, Tianjin, Zhengzhou and Wuhan, respectively. The reductions in emissions of PM_2.5 precursors were ~2 times of that in concentrations, indicating that meteorology was unfavorable during simulation episode. A further analysis shows that benefits of emission reductions were overwhelmed by adverse meteorology and severe air pollution events were not avoided. This study highlights that large emissions reduction in transportation and slight reduction in industrial would not help avoid severe air pollution in China, especially when meteorology is unfavorable. More efforts should be made to completely avoid severe air pollution.

Enhanced secondary pollution offset reduction of primary emissions during COVID-19 lockdown in China

To control the spread of the 2019 novel coronavirus (COVID-19), China imposed nationwide restrictions on the movement of its population (lockdown) after the Chinese New Year of 2020, leading to large reductions in economic activities and associated emissions. Despite such large decreases in primary pollution, there were nonetheless several periods of heavy haze pollution in eastern China, raising questions about the well-established relationship between human activities and air quality. Here, using comprehensive measurements and modeling, we show that the haze during the COVID lockdown was driven by enhancements of secondary pollution. In particular, large decreases in NO_x emissions from transportation increased ozone and nighttime NO₃ radical formation, and these increases in atmospheric oxidizing capacity in turn facilitated the formation of secondary particulate matter. Our results, afforded by the tragic natural experiment of the COVID-19 pandemic, indicate that haze mitigation depends upon a coordinated and balanced strategy for controlling multiple pollutants.