Research on ozone formation sensitivity based on observational methods: Development history, methodology, and application and prospects in China

Observation-based method for O3 formation sensitivity research is an important tool to analyze the causes of ground-level O3 pollution, which has broad application potentials in determining the O3 pollution formation mechanism and developing prevention and control strategies. This paper outlined the development history of research on O3 formation sensitivity based on observational methods, described the principle and applicability of the methodology, summarized the relative application results in China and provided recommendations on the prevention and control of O3 pollution in China based on relevant study results, and finally pointed out the shortcomings and future development prospects in this field in China. The overview study showed that the O3 formation sensitivity in some urban areas in China in recent years presented a gradual shifting tendency from the VOC-limited regime to the transition regime or the NOx-limited regime due to the implementation of the O3 precursors emission reduction policies; O3 pollution control strategies and precursor control countermeasures should be formulated based on local conditions and the dynamic control capability of O3 pollution control measures should be improved. There are still some current deficiencies in the study field in China. Therefore, it is recommended that a stereoscopic monitoring network for atmospheric photochemical components should be further constructed and improved; the atmospheric chemical mechanisms should be vigorously developed, and standardized methods for determining the O3 formation sensitivity should be established in China in the near future.

Design of Ca-type todorokite catalysts with highly active for the selective reduction of NOx by NH3 at low temperatures

Ca-type todorokite catalysts were designed and prepared by a simple redox method and applied to the selective reduction of NOx by NH3 (NH3-SCR) for the first time. Compared with the Na-type manjiroite prepared by the same method, the todorokite catalysts with different Mn/Ca ratios showed greatly improved catalytic activity for NOx reduction. Among them, Mn8Ca4 catalyst exhibited the best NH3-SCR performance, achieving 90% NOx conversion within temperature range of 70-275°C and having a high sulphur resistance. Compared to the Na-type manjiroite sample, Ca-type todorokite catalysts possessed an increased size of tunnel, resulting in a larger specific surface area. As increased the amounts of Ca doping, the Na content in Ca-type todorokite catalysts significantly decreased, providing larger amounts of Brønsted acid sites for NH3 adsorption to produce NH4+. The NH4+ species were highly active for reaction with NO + O2, playing a determining role in NH3-SCR process at low temperatures. Meanwhile, larger amounts of surface adsorbed oxygen contained over the Ca-doping samples than that over Na-type manjiroite, promoting the oxidation of NO and fast SCR processes. Over the Ca-type todorokite catalysts, furthermore, nitrates produced during the flow of NO + O2, were more active for reaction with NH3 than that over Na-type manjiroite, benefiting the occurrence of NH3-SCR process. This study provides novel insights into the design of NH3-SCR catalysts with high performance.

A machine learning-based ensemble model for estimating diurnal variations of nitrogen oxide concentrations in Taiwan

Air pollution is inextricable from human activity patterns. This is especially true for nitrogen oxide (NOx), a pollutant that exists naturally and also as a result of anthropogenic factors. Assessing exposure by considering diurnal variation is a challenge that has not been widely studied. Incorporating 27 years of data, we attempted to estimate diurnal variations in NOx across Taiwan. We developed a machine learning-based ensemble model that integrated hybrid kriging-LUR, machine-learning, and an ensemble learning approach. Hybrid kriging-LUR was performed to select the most influential predictors, and machine-learning algorithms were applied to improve model performance. The three best machine-learning algorithms were suited and reassessed to develop ensemble learning that was designed to improve model performance. Our ensemble model resulted in estimates of daytime, nighttime, and daily NOx with high explanatory powers (Adj-R2) of 0.93, 0.98, and 0.94, respectively. These explanatory powers increased from the initial model that used only hybrid kriging-LUR. Additionally, the results depicted the temporal variation of NOx, with concentrations higher during the daytime than the nighttime. Regarding spatial variation, the highest NOx concentrations were identified in northern and western Taiwan. Model evaluations confirmed the reliability of the models. This study could serve as a reference for regional planning supporting emission control for environmental and human health.

Performance evaluation of PM, NOx, and hydrocarbon removal in diesel engine exhaust by surface discharge-induced plasma

Diesel engines are characterized by low CO2 emissions and high fuel efficiency. However, their exhausts contain nitrogen oxides (NOx), particulate matter (PM), and hydrocarbons (HC) that require removal by aftertreatment. A novel low-temperature plasma-based aftertreatment method has been developed for the simultaneous removal of NOx, PM, and HC. NOx could be reduced by reacting with HC and CO in the exhaust gas. The particle and gas concentrations in the exhaust are measured using a scanning mobility particle sizer, a NOx analyzer, and a total hydrocarbon analyzer. The treatment performance is evaluated using the resulting measurements. The diesel engine is operated under 0%, 25%, 50%, and 75% loads (maximum output of 2 kW), and the exhaust gas is mixed with N2 + O2 (13%) gas. The power is adjusted to provide 100, 200, 300, and 400 W input power during the plasma reactor treatment. The aftertreatment removal of NOx, PM, and HC is evaluated, and the engine exhibits a removal efficiency of 70% for NOx, 98% for PM, and 67% for HC at 75% engine load and an input power of 100 W.

Dual function of H2O on interfacial intermediate conversion and surface poisoning regulation in simultaneous photodegradation of NO and toluene

Co-existing air pollutants, especially NOx and VOCs, will generate secondary photochemical pollution under light irradiation. However, simultaneous elimination of multi-pollutants has long been a challenge. Photocatalysis could turn the reaction pathway between pollutants to convert them into harmless products, which is a promising technology for multi-pollutant control. Here we achieved synergistic photocatalytic degradation of NO and C7H8 on InOOH photocatalyst, and the performance can be adjusted by H2O through affecting the interaction between surface species and catalyst. In situ DRIFTS and GC-MS revealed that the improved efficiency originated from the fast conversion of C-N coupling intermediates led by additional H2O. Surface characterizations and DFT simulation determined that accumulated nitrates will compete with the adsorption of NO and C7H8, resulting in a decline in efficiency in the later stage. Although improved efficiency would bring more nitrates, as H2O has comparable adsorption to nitrate at the same site, high humidity can mitigate the deactivation. The photocatalyst can be also simply regenerated by water washing. This work reveals the complex interaction in the multi-pollutant system and provides guidelines for precisely regulating the synergistic removal of NOx and VOCs.

Health impacts under different ozone mitigation pathways in Beijing-Tianjin-Hebei and its surroundings

To evaluate the effects of the various ozone (O₃) control approaches on environmental health and health inequalities, 121 reduction scenarios for nitrogen oxides (NO_x) and volatile organic compounds (VOCs) were developed, and their environmental health impacts were calculated. With the target of achieving the 90th percentile of the daily maximum 8 h mean O₃ concentration (MDA8-90th) of 160 μg/m³ in Beijing-Tianjin-Hebei and its surroundings ("2 + 26" cities), three typical scenarios namely, High-NO_x reduction ratio (HN, NO_x/VOCs = 6:1), High-VOCs reduction ratio (HV, NO_x/VOCs = 3:7), and Balanced reduction ratio (Balanced, NO_x/VOCs = 1:1) were investigated. The results show that O₃ formation is currently NO_x-limited at the regional scale, while some developed cities are VOC-limited, indicating that NO_x mitigation should be the core for achieving the targeted concentration (160 μg/m³) at the regional scale, whereas cities such as Beijing in the short term should focus on VOCs mitigation. The population-weighted O₃ concentrations in the HN, Balanced, and HV scenarios were 159.19, 159.19, and 158.44 μg/m³, respectively. In addition, the O₃-related premature mortality was 41,320 in "2 + 26" cities; control measures under HN, Balanced, and HV could potentially decrease O₃-related premature deaths by 59.94 %, 60.25 %, and 71.48 %, respectively. The HV scenario has been found to be more advantageous in lowering the O₃-related environmental health impacts than the HN and Balanced scenarios. It was further found that premature deaths avoided by the HN scenario were mainly concentrated in economically unadvanced regions, whereas those prevented by the HV scenario were mainly concentrated in developed cities. This may lead to geographical inequities in environmental health. As ozone pollution in large cities with high population density is primarily VOC-limited, decrease in VOCs should be focused on in the short term to avoid more O₃-related premature deaths, whereas NO_x control may be more important in decreasing ozone concentrations and ozone-related mortality in the future.

The importance of data splitting in combined NOx concentration modelling

The polluted air breathed every day by those living in large conurbations poses a significant risk to their health. Through effective modelling (prediction) of concentrations of pollutants and identification of the factors influencing them, it should be possible to obtain advance information on dangers and to plan and implement measures to reduce them. This work describes two different modelling approaches: based on the NO_x concentration of the previous hour (C&RT models); and based on meteorological factors, traffic flow, and past (up to two previous hours) NO_x and NO₂ concentrations (CA models). For each approach, three alternative machine learning methods were applied: artificial neutral network (ANN), random forest (RF), and support vector regression (SVR). The best fits were obtained for the models using ANN and RF (MAPE values in the range 18.3-18.5 %). Poorer fits were found for the SVR models (MAPE equal to 23.4 % for the C&RT approach and 29.3 % for CA). No significant preferences were identified between the C&RT and CA approaches (based on various goodness-of-fit measures). The choice should be determined by the purposes for which the forecast is to be used.

The air quality impacts of pre-operational hydraulic fracturing activities

Hydraulic fracturing (fracking) is a short phase in unconventional oil and natural gas (O&G) development. Before fracking there is a lengthy period of preparation, which can represent a significant proportion of the well lifecycle. Extensive infrastructure is delivered onto site, leading to increased volumes of heavy traffic, energy generation and construction work on site. Termed the "pre-operational" period, this is rarely investigated as air quality evaluations typically focus on the extraction phase. In this work we quantify the change in air pollution during pre-operational activities at a shale gas exploration site near Kirby Misperton, North Yorkshire, England. Baseline air quality measurements were made two years prior to any shale gas activity and were used as a training dataset for random forest (RF) machine learning models. The models allowed for a comparison between observed air quality during the pre-operational phase and a counterfactual business as usual (BAU) prediction. During the pre-operational phase a significant deviation from the BAU scenario was observed. This was characterised by significant enhancements in NO_x and a concurrent reduction in O₃, caused by extensive additional vehicle movements and the presence of combustion sources such as generators on the well pad. During the pre-operational period NO_x increased by 274 % and O₃ decreased by 29 % when compared to BAU model values. There was also an increase in primary emissions of NO₂ during the pre-operational phase which may have implications for the attainment of ambient air quality standards in the local surroundings. Unconventional O&G development remains under discussion as a potential option for improving the security of supply of domestic energy, tensioned however against significant environmental impacts. Here we demonstrate that the preparative work needed to begin fracking elevates air pollution in its own right, a further potential disbenefit that should be considered.

Novel synthesis of reed flower-like SmMnOx catalyst with enhanced low-temperature activity and SO2 resistance for NH3-SCR

In this work, a novel co-precipitation coupled solvothermal procedure is proposed to prepare a SmMnO_x catalyst (SmMnOx-CP + ST) with a reed flower-like structure for the selective catalytic reduction of NO_x by NH₃ (NH₃-SCR). Over 90% NO_x conversion and N₂ selectivity was achieved at a low temperature range (25-200 °C), and 96% NO_x conversion was achieved in the presence of 100 ppm SO₂ at 75 °C. While the NH₃-SCR of the SmMnO_x catalysts prepared by co-precipitation (SmMnO_x-CP) and solvothermal (SmMnO_x-ST) methods performed much poorer than the SmMnO_x-CP + ST catalyst. All catalysts were characterized by XRD, BET, SEM, XPS, H₂-TPR, NH₃-TPD, NO_x-TPD, and FT-IR. The results revealed that the superior performance of the SmMnO_x-CP + ST is due to the unique reed flower-like structure morphology, which endows the SmMnO_x-CP + ST with the largest surface area, the strongest synergistic reaction of Sm and Mn, abundant surface oxygen species and surface active sites, and significantly enhances the redox ability. Furthermore, the amorphous reed flower-like structure showed strong short-range ordered interaction between the active components and weaken the formation of sulfates species. In addition, the highest content of Mn⁴⁺ and Mn³⁺+Mn⁴⁺ greatly promotes the redox cycles of Sm²⁺↔Mn⁴⁺ and Sm²⁺↔Mn³⁺, and suppresses the production of sulfate species in the presence of SO₂.

On reducing the emissions of CO, HC, and NOx from gasoline blended with hydrogen peroxide and ethanol: Optimization study aided with ANN-PSO

The use of ethanol blending for gasoline has been found to have a significant effect in reducing emissions without any loss in the performance of a spark ignition engine. However, an increase in the emissions of oxides of nitrogen (NO_x) may be seen due to the increased oxygen content in the fuel. On the contrary, emulsifying fuel with hydrogen peroxide (H₂O₂) has shown a substantial effect in reducing all the emissions, including NO_x in a compression ignition (CI) engine. In this study, 10% ethanol is blended with gasoline (E10) and further emulsified with H₂O₂ up to 1.5%. When compared to neat gasoline, a 4.8% increase in brake thermal efficiency (BTE) is obtained with 10% ethanol and 1.5% H₂O₂. The corresponding average decrease in the emissions of carbon monoxide (CO), hydrocarbons (HC), and NO_x were 80%, 43%, and 17%, respectively. The results of the experimental trials are used to model an artificial neural network (ANN) to derive a relationship between the input factors of ethanol concentration, H₂O₂ concentration, and engine speeds with the output responses of BTE, CO, HC, and NO_x. The ANN models of each response are optimized using a multi-objective particle swarm optimization (PSO) for maximizing BTE and minimizing emissions of CO, HC, and NO_x. The PSO results showed that operating the engine at 2000 rpm using ethanol blending between 4 and 6% and H₂O₂ emulsification of 1.5% are the best optimal conditions.

Deposition-mediated phytoremediation of nitrogen oxide emissions

The growing global population and use of natural resources lead to significant air pollution. Nitrogen oxide emissions is a potential killer threatening human health requiring focus and remediation using vegetation being efficient and cheap. Here we review the mechanisms of removing nitrogen oxides by dry deposition of plants, discussing the principle of leaf absorption of pollutants and factors affecting the removal of nitrogen oxides providing a theoretical basis for the selection of urban greening vegetation.

Nitrogen isotopic composition of NOx from residential biomass burning and coal combustion in North China

Stable nitrogen isotope (δ¹⁵N) technology has often been used as a powerful tool to separate nitrogen oxides (NO_x) produced by residential combustion (i.e., biomass burning and coal combustion) from other sources. However, the insufficient measurement of δ¹⁵N-NO_x fingerprints of these emissions limits its application, especially in North China where residential emissions are significant. This study conducted combustion experiments to determine the δ¹⁵N-NO_x of typical residential fuels in North China, including ten biomass fuels and five types of coal. The results showed that the δ¹⁵N of biomass varied between -6.9‰ and 2.3‰, which was lower than the δ¹⁵N of residential coal (-0.2‰-4.6‰). After combustion, the δ¹⁵N of biomass residues increased greatly, while that of coal residues showed no significant upward trend (p > 0.05). The δ¹⁵N-NO_x produced by biomass burning ranged from -5.6‰ to 3.2‰ (-0.4‰ ± 2.4‰), showing a significant linear relation with δ¹⁵N-biomass. Comparatively, the δ¹⁵N-NO_x derived from residential coal combustion was much higher (16.1‰ ± 3.3‰), ranging from 11.7‰ to 19.7‰. It was not well correlated with δ¹⁵N-coal, and only slightly lower than the estimated δ¹⁵N-NO_x of industrial coal combustion (17.9‰, p > 0.05). These observations indicate that the δ¹⁵N-NO_x of residential coal combustion is a result of the mixture of thermal- and fuel-released NO_x. Based on the isotopic characteristics observed in this study, we analyzed the reported δ¹⁵N-NO_x, and provided more statistically robust δ¹⁵N-NO_x distributions for biomass burning (1.3‰ ± 4.3‰; n = 101) and coal combustion (17.9‰ ± 3.1‰; n = 26), which could provide guidance for scientific studies aiming to quantify the origin of NO_x in North China and in other regions.

Evolution of aerosol chemistry in Beijing under strong influence of anthropogenic pollutants: Composition, sources, and secondary formation of fine particulate nitrated aromatic compounds

Nitrated aromatic compounds (NACs) constitute a key segment of brown carbon (BrC), thereby contributing to the light-absorbing characteristics of aerosols in the atmosphere. However, until recently, there is a scarcity of research on their generation in the urban environment. The current study is based upon an extensive field study of NACs from fine particle samples obtained at an urban location in Beijing in the spring and summer of 2017, which was characterized by both high anthropogenic volatile organic compounds (VOCs) and high-NO_x dominated conditions. The mean total concentration of the nine NACs was 8.58 ng m^-3 in spring and 8.54 ng m^-3 in summer. In the spring, the most abundant NACs were 4-nitrophenol (33.7%) and 4-nitrocatechol (19.3%), while in the summer, the most abundant NACs were 4-nitroguaiacol (34.9%) and 2, 4-dinitrophenol (23%). Atmospheric NACs were primarily produced from coal combustion (52%) and biomass burning (32%) in spring, and originated from the secondary formation (37%) and traffic (35%) in summer. NO₂ could promote the formation of NACs with a significant effect on their compositions, especially for nitrophenols and nitrocatechols. It can also affect the formation of nitrated aerosols and their existing form. Inorganic nitrates were increased to conversion in the daytime when NO₂ concentrations were higher than 30 ppb, but the corresponding oxidation products shifted to primarily organic ones at night. The transition was VOC-sensitive regimes for NAC formation, and nitration of toluene was a more important pathway during the campaign in Beijing.

Variations of significant contribution regions of NOx and PN emissions for passenger cars in the real-world driving

Nitrogen oxides (NO_x) and particulate number (PN) emissions are the main concerns of the passenger cars in the real-world driving. NO_x and PN emissions are greatly dependent on the driving behaviors which differ significantly between standard driving cycles and real-world driving. However, the significant contribution regions (short durations corresponding to high proportions of total emissions) of NO_x and PN emissions regarding different driving behaviors (e.g. vehicle speed and acceleration) are still uncovered. NO_x20% and NO_x50% refer to instantaneous NO_x emission rates when NO_x emission rates are ranked from high to low level where the sums of NO_x emission rates being higher than NO_x20% and NO_x50% correspond to 20% and 50% of total NO_x emissions, respectively. t_20% and t_50% are corresponding durations where NO_x emission rates are higher than NO_x20% and NO_x50%. In this paper, three Euro-6 compliant direct injection gasoline passenger cars and a diesel passenger car are tested in a real-world driving trial in which nineteen drivers are involved. Novel key performance indicators with reference to the regimes of specific NO_x and PN contributions to total emissions are defined. Instantaneous NO_x and PN emissions are monitored using a portable emission measurement system (PEMS) in the test. The results indicate that the maximum and minimum average speed over the four cars being approximately 32.3 km/h s and 42.6 km/h, respectively. Average PN emission factor of the diesel car is the lowest among the four given cars. Average t_20% and t_50% corresponding to NO_x20% and NO_x50% are lower than 3% and 12%, respectively, for all the passenger cars; additionally, these two parameters show the same pattern. The corresponding t_20% and t_50% variations of the Euro-6a gasoline car and the diesel car are much lower than the other two. Average acceleration corresponding to 20% and 50% of total NO_x emissions for the given diesel car is approximately 1.25 m/s² and 0.6 m/s², respectively, being much higher than that of the other three gasoline cars (lower than 1 m/s² and 0.4 m/s² respectively) over the specific driving route and drivers. The average PN_20% and PN_50% of the given diesel car are approximately 7 × 10⁷#/s and 3 × 10⁷#/s respectively, being much lower than the three given gasoline cars (higher than 8 ×10⁹#/s and 2 ×10⁹#/s respectively) under the given test conditions; the corresponding t_20% and t_50% are lower than 4% and 17% respectively for all the three gasoline cars.

Abatement of NO/SO2/Hg0 from flue gas by advanced oxidation processes (AOPs): Tech-category, status quo and prospects

This review article provides a state-of-art insight into the removal of NO, SO₂ and elemental mercury (Hg⁰) from flue gas by using advanced oxidation processes (AOPs) method. Firstly, the main flue gas purification strategies based on AOPs would be classified as gas-gas, gas-liquid and gas-solid systems preliminarily, and the primary chemistry/mechanism of the above homogeneous/heterogeneous reaction systems were presented as the oxidation of NO, SO₂ and Hg⁰ by the oxidative free radicals (OH, O₂ and SO₄^-etc.). Secondly, the research progress and reaction pathways for separately or simultaneously removing NO, SO₂ and Hg⁰ from flue gas by AOPs has been reviewed elaborated and analyzed in more details. Notably, the wet/dry oxidation coupled with efficient absorption process would be a promising method of efficient removal of above gaseous pollutants. Subsequently, four types of assumed layout modes were described graphically. The application prospects of AOPs for the purification of flue gas from coal-fired boiler or industrial furnace were evaluated and found that the operation cost and utilization of oxidants must be reduced and improved respectively. Finally, the limitations in the current removal technologies based on AOPs are highlighted, meanwhile the future research directions are suggested, such as cut down the cost of oxidants and catalysts, improve the yield and valid utilization of highly reactive radicals and enhance the reactivity, resistance and stability of catalysts. Significantly, it is also envisaged that the review could enrich the knowledge repository to function as a scientific reference for the sustainable development of economical, effective and environment-friendly technologies for the abatement of a wide variety of emissions from flue gas, and further improve the feasibility and reliability of the strategies for moving from laboratory studies to large-scale development and industrial application.

Unraveling SO2-tolerant mechanism over Fe2(SO4)3/TiO2 catalysts for NOx reduction

Developing low-temperature SO₂-tolerant catalysts for the selective catalytic reduction of NO_x is still a challenging task. The sulfation of active metal oxides and deposition of ammonium bisulfate deactivate catalysts, due to the difficult decomposition of the as-formed sulfate species at low temperatures (<300 °C). In recent years, metal sulfate catalysts have attracted increasing attention owing to their good catalytic activity and strong SO₂ tolerance at higher temperatures (>300°C); however, the SO₂-tolerant mechanism of metal sulfate catalysts is still ambiguous. In this study, Fe₂(SO₄)₃/TiO₂ and Ce₂(SO₄)₃/TiO₂ catalysts were prepared using the corresponding metal sulfate salt as the precursor. These catalysts were tested for their low-temperature activity and SO₂ tolerance activity. Compared to Ce₂(SO₄)₃/TiO₂, Fe₂(SO₄)₃/TiO₂ showed significantly better low-temperature activity and SO₂ tolerance. It was demonstrated that less surface sulfate species formed on Fe₂(SO₄)₃/TiO₂ and Ce₂(SO₄)₃/TiO₂. However, the presence of NO and O₂ could assist the decomposition of NH₄HSO₄ over Fe₂(SO₄)₃/TiO₂ at a lower temperature, endowing Fe₂(SO₄)₃/TiO₂ with better low-temperature SO₂ tolerance than Ce₂(SO₄)₃/TiO₂. This study unraveled the SO₂-tolerant mechanism of Fe₂(SO₄)₃/TiO₂ at lower temperatures (<300 °C), and a potential strategy is proposed for improving the low-temperature SO₂-tolerance of catalysts with Fe₂(SO₄)₃ as the main active component or functional promoter.

Flue gas torrefaction of distilled spirit lees and the effects on the combustion and nitrogen oxide emission

Flue gas torrefaction (FGT) integrated with combustion was introduced for the clean treatment of distilled spirit lees (DSL). The effects of temperature, residence time, and volumetric flow rate of FGTs were investigated. The improvement in the physicochemical and combustion characteristics of the torrefied DSL and the reaction mechanisms were clarified by a tube furnace and the TG-MS device. The results showed that FGT could effectively improve the properties of DSL. With increasing temperature, residence time, and volumetric flow rate, the mass and energy yields decreased. FGT showed positive effects on the removal of free and bonding water, as well as the enrichment of lignin. FGT effectively inhibited the release of NO_x. The overall emission of NO_x was reduced by 57.3%. Additionally, the cost of DSL drying and denitrification could be greatly reduced by FGT. This study provided a practical treatment for DSL and new insight into FGT.

NOx absorption and conversion by ionic liquids

Ionic liquids (ILs) can be used as absorbents and catalysts for NO_x absorption and conversion due to their low toxicity, low energy consumption and excellent reusability. The capacity and absorption mechanism of NO_x absorption by ILs are presented in this paper. Generally, NO_x are physically absorbed by conventional ILs such as imidazolium-based ILs. The absorption capacity is as follows: NO₂>NO>N₂O, which is in good agreement with the binding energy between NO_x and ILs. Furthermore, low temperature, high pressure and large cation volume are favorable for NO_x absorption. The strategies of enhancing NO_x capacity through functionalized ILs with metal-containing anions (e.g. [FeCl₄]^2-), amine groups, sulfonate and carboxylate anions are also concluded. Active N or O sites in functionalized ILs can react with the dimer of NO (N₂O₂), resulting in high capacity. Moreover, introducing electron-withdrawing substituents such as chlorine and bromine into carboxylate or sulfonate anions reduces desorption residue. Besides NO_x absorption, ILs with [NO₃]^- can activate NO and efficiently catalyze its conversion into HNO₃ in the presence of O₂ and H₂O, and have better performance than ILs with [Cl]^-, [Ac]^- and [CF₃SO₃]^-, which is attributed to the strong oxidization capability of [NO₃]^-. In addition, low temperature and high O₂ content can further improve NO conversion.

Microbiota profiling in aging-associated inflammation and liver degeneration

BACKGROUND

The number of people above the age of 60 years is raising world-wide being associated with an increase in the prevalence of aging-associated impairments and even diseases. Recent studies suggest that aging is associated with alterations in bacterial endotoxin levels and that these changes may add to low-grade inflammation, the so-called 'inflammaging', and aging-associated liver degeneration. However, mechanisms involved, and especially, the interaction of intestinal microbiota and barrier in the development of aging-associated inflammation and liver degeneration have not been fully understood.

OBJECTIVE

The aim of the present study was to determine if intestinal microbiota composition changes with age and if these alterations are associated with changes of markers of intestinal barrier function and the development of inflammation and liver degeneration.

METHODS

Blood, liver, small and large intestinal tissue of male 2-, 15-, 24- and 30-months old C57BL/6 mice fed standard chow were obtained. Intestinal microbiota composition, expression levels of antimicrobial peptides in small intestine and markers of intestinal barrier function were measured. Furthermore, indices of liver damage, inflammation and expression levels of lipopolysaccharide binding protein (Lbp) as well as of toll-like receptors (Tlr) 1-9 in liver tissue were assessed.

RESULTS

Pairwise comparisons of the microbial community in the small intestine showed differences between 2- and 24-, 15- and 24-, as well as 15- and 30-months old animals while Shannon's diversity, species richness and evenness indexes did not differ in both small and large intestine, respectively, between age groups. Concentrations of nitric oxide were significantly lower in small intestine of 15-, 24- and 30-months old mice compared to 2-months old mice while mRNA expression of the antimicrobial peptides defensin alpha 1 and lysozyme 1 was unchanged. In contrast, in liver tissue, older age of animals was associated with increasing inflammation and the development of fibrosis in 24- and 30-months old mice. Numbers of inflammatory foci and neutrophils in livers of 24- and 30-months old mice were significantly higher compared to 2-months old mice. These alterations were also associated with higher endotoxin levels in plasma as well as an increased mRNA expression of Lbp and Tlr1, Tlr2, Tlr4, Tlr6 and Tlr9 in livers in older mice.

CONCLUSION

Despite no consistent and robust changes of microbiota composition in small and/or large intestine of mice of different age were observed, our data suggest that alterations of markers of intestinal barrier function in small intestine are associated with an induction of several Tlrs and beginning hepatic inflammation in older mice and increase with age.

Early observations on the impact of the COVID-19 lockdown on air quality trends across the UK

UK government implemented national lockdown in response to COVID-19 on the 23-26 March 2020. As elsewhere in Europe and Internationally, associated restrictions initially limited individual mobility and workplace activity to essential services and travel, and significant air quality benefits were widely anticipated. Here, break-point/segment methods are applied to air pollutant time-series from the first half of 2020 to provide an independent estimate of the timings of discrete changes in NO, NO₂, NO_x, O₃, PM₁₀ and PM_2.5 time-series from Automatic Urban Rural Network (AURN) monitoring stations across the UK. NO, NO₂ and NO_x all exhibit abrupt decreases at the time the UK locked down of (on average) 7.6 to 17 μg·m^-3 (or 32 to 50%) at Urban Traffic stations and 4 to 5.7 μg·m^-3 (or 26 to 46%) at Urban Background stations. However, after the initial abrupt reduction, gradual increases were then observed through lockdown. This suggests that the return of vehicles to the road during early lockdown has already offset much of the air quality improvement seen when locking down (provisional estimate 50 to 70% by 01 July). While locking down O₃ increased (7 to 7.4 μg·m^-3 or 14 to 17% at Urban stations) broadly in line with NO₂ reductions, but later changes suggest significant non-lockdown contributions to O₃ during the months that followed. Increases of similar magnitudes were observed for both PM₁₀ (5.9 to 6.3 μg·m^-3) and PM_2.5 (3.9 to 5.0 μg·m^-3) at both Rural and Urban stations alike, but the distribution of changes suggests the lockdown was not an obvious direct source of changes in levels of either of these species during this period, and that more complex contributions, e.g. from resuspension and secondary aerosol, may be more likely major drivers for these changes.

A comprehensive study on ozone pollution in a megacity in North China Plain during summertime: Observations, source attributions and ozone sensitivity

Tropospheric ozone (O₃) pollution has been becoming prominent in North China Plain (NCP) in China since last decade. In order to clarify the source contribution and formation mechanism of O₃, the critical precursors of volatile organic compounds (VOCs) were measured with both on-line and off-line methods in Luoyang City in summer of 2019. The concentrations of nitrogen oxides (NO_x, sum of NO and NO₂) and O₃ were simultaneously monitored. Fifty-seven VOCs measured in U.S. Photochemical Assessment Monitoring Station (PAMS) showed daily concentrations in a range of 14.5 ± 5.33 to 29.2 ± 11.2 ppbv in Luoyang, which were comparable with those in other Chinese megacities. The mass compositions of VOCs were determined, with comparatively low proportions of alkanes (<50%) but high fractions of photoreactive alkenes and alkyne. Source apportionment of VOCs was conducted by Hybrid Environmental Receptor Model (HERM). The results indicated that industrial (38.5%) and traffic (32.0%) were the two dominated pollution sources of VOCs in the urban, while the biogenic and residential sources had contributions of 15.8% and 13.8%, respectively. To further measure the O₃ formation sensitivity and its source attribution, the WRF-CHEM model was adopted in this study. The variation of O₃ between the observation and the stimulation using the local emission inventory showed an index of agreement (IOA) of 0.85. The simulation conducted by WRF-CHEM indicated an average of 43.5% of the O₃ was associated with the regional transportation, revealing the importance of inter-regional prevention and control policy. Traffic and biogenic emissions were the two major pollution sources to an O₃ episode occurred from July 21 to July 27, 2019 (when O₃ concentration over 150 μg m^-3) in Luoyang, with average contributions of 22.9% and 18.3%, respectively. The O₃ isopleths proved that its formation in the atmosphere of Luoyang was in transitional regime and collectively controlled by both VOCs and NO_x. This was different from the observations in main cities of NCP before implantations of strict emission controls. The isopleths additionally designated that the O₃ formation regime would move forward or shift to NO_x regime after a reduction of over 45% during the episode. Similar patterns were also reported in other Chinese megacities such as Beijing and Shanghai, due to the tightening of the NO_x control policies. Our results do support that the simultaneous controls of NO_x and VOCs were effective in reductions of tropospheric O₃ in Luoyang. Meanwhile, joint regional control policies on the emissions of NO_x and VOCs can potentially overwhelm the current O₃ pollutions in China.

Surface ozone exceedances in Melbourne, Australia are shown to be under NOx control, as demonstrated using formaldehyde:NO2 and glyoxal:formaldehyde ratios

Two and a half years of multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements of nitrogen dioxide (NO₂), formaldehyde (HCHO) and glyoxal (CHOCHO) are presented alongside in-situ ozone (O₃) measurements in Melbourne, Australia. Seasonal and diurnal cycles, vertical profiles and relationships with key meteorological variables are provided. NO₂ and CHOCHO were found at highest concentration for low wind speeds implying that their sources were predominantly localised and anthropogenic. HCHO showed an exponential relationship with temperature and a strong wind direction dependence from the northern and eastern sectors, and therefore most likely originated from oxidation of biogenic volatile organic compounds (VOCs) from surrounding forested and rural areas. The glyoxal:formaldehyde ratio (R_gf), reported for the first time in Australia, was consistently high compared to values elsewhere in the world with a mean of 0.105 ± 0.0503 and tended to increase with increasing anthropogenic influence. The HCHO:NO₂ ratio (R_fn) was used to characterise tropospheric ozone formation conditions. A strong relationship was found between high temperature, low R_gf, high R_fn and high ozone surface concentrations. Therefore, we propose that both R_gf and R_fn may be useful indicators of tropospheric ozone production regimes and concentrations. The R_fn showed that the vast majority of high ozone production episodes occurred under NO_x-limited conditions, suggesting that surface ozone pollution events in Melbourne could be curtailed using NO_x emission controls.

Gas phase sulfation of ceria-zirconia solid solutions for generating highly efficient and SO2 resistant NH3-SCR catalysts for NO removal

A series of ceria-zirconia solid solutions (Ce_xZr_1-xO₂) were prepared by co-precipitation method and then sulfated with SO₂ + O₂ at 200 °C. Subsequent testing with the selective catalytic reduction of NO by NH₃ (NH₃-SCR) showed that the activity of the sulfated Ce_xZr_1-xO₂ catalysts oxide catalysts exhibited a volcano-type tendency with increasing Zr content. Furthermore, the sulfated Ce_0.6Zr_0.4O₂ catalyst showed the most desirable NH₃-SCR activity at 250-300 °C, and exhibited much better SO₂ resistance at 250 °C. Detailed characterization results demonstrated that Ce_0.6Zr_0.4O₂ could adsorb more surface sulfate species and then produce more stable acid sites than pure CeO₂ at 200 °C. After sulfation treatment, more Ce³⁺ and oxygen vacancies were formed on the surface of Ce_0.6Zr_0.4O₂. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) experiments suggested that the nitrates species deposited on the surface of as-prepared Ce_0.6Zr_0.4O₂, which showed no reactivity, could barely deposit on the same sample after sulfation. While, the sulfated Ce_0.6Zr_0.4O₂ had more reactive acid sites to participate in the NH₃-SCR and the reaction proceeded via Eley-Rideal mechanism. This work proved that sulfation treatment could be used in designing an efficient cerium-zirconium based NH₃-SCR catalyst with great application prospect.

Estimating the nitrogen source apportionment of Sophora japonica in roadside green spaces using stable isotope

It is generally accepted that urban vegetation absorbs air pollutants resulting in improved air quality. However, limited work has provided experimental data that can be used to quantify this. In this study, Sophora japonica in the near-road environment was studied, and stable isotopes were used to estimate the proportional contributions of different nitrogen sources to the trees. δ¹⁵N and δ¹⁸O values were quantified for plant (n = 254) and soil samples (n = 86) collected from 12 sampling sites in Beijing. The elemental composition (total nitrogen (TN) and total carbon (TC)) of both samples types, and the ionic concentration (NO₃^- and NH₄⁺) of soil samples were also measured. δ¹⁵N in S. japonica sampled near the road was significantly lower than in samples collected far from the road. Variation of δ¹⁸O, TN, and TC in plant samples could not be explained by the road distance. Using the SIAR Bayesian isotope mixing model and the mixing polygon method, the average proportional contributions of three nitrogen sources for the tree samples among all experiment sites were estimated, with the proportion for each nitrogen source following the order: soil (69.2%) > traffic-related NO_x (19.3%) > dry deposition (11.5%). In addition, the results of the Bayesian model revealed that the nitrogen contribution of traffic-related NO_x at road-adjacent sites (23.0%) was higher than the contribution of traffic-related NO_x at sites far from the road (16.4%). These results indicated that the S. japonica in near-road green spaces was significantly influenced by traffic-related NO_x emissions that were characterized by lower δ¹⁵N values. We found that using the SIAR Bayesian isotope mixing model and mixing polygon method, the potential nitrogen sources of plants could be estimated and the proportional contributions estimated by the model can reflect the plant's ability to absorb air-borne NO_x.

A study on the CO2 and NOx emissions performance of Euro 6 diesel vehicles under various chassis dynamometer and on-road conditions including latest regulatory provisions

The current study presents a detailed analysis of the gaseous emissions, focusing on CO₂ and NO_x, of diesel vehicles under several operating conditions. An assessment is also made on the impact and effectiveness of the Real Driving Emissions (RDE) test, which is mandatory by the European Union (EU) type approval regulation for passenger cars since September 2017. The method followed comprises emissions measurement tests on three Euro 6 diesel vehicles, under laboratory and various on-road operation conditions. Chassis dynamometer tests in the laboratory showed that emissions over the current type approval test (World-wide harmonized Light-duty Test Procedure or WLTP), and over the former one (New European Driving Cycle or NEDC), poorly reflect real-world levels. However, the most demanding CADC testing comes closer to real drive emissions. Comparison of driving conditions on the chassis dynamometer over different driving cycles and on the road reveals that the emission performance substantially varies between different tests, even for apparently similar operation conditions. The NO_x emissions reduction strategy of pre-RDE monitoring Euro 6 vehicles seems to be optimized for the NEDC driving conditions, which are not representative of the real-world driving conditions. The real-world emissions during normal driving conditions are effectively captured with the new RDE test, however driving the vehicle dynamically, at conditions outside the RDE regulation boundaries, results to disproportional high emissions. This is a significant shortcoming which might be critical for populations living on hilly areas or those close to specific micro-environments, such as highway entrance ramps, traffic lights, etc.

Heavy metal poisoned and regeneration of selective catalytic reduction catalysts

Being poison to heterogeneous catalysts, Pb and As are important metals in the study of industrial NO_x emission reductions. A series of V₂O₅-WO₃/TiO₂-SiO₂ catalysts poisoned by Pb and As were prepared through wet impregnation. The regeneration effect of deionized water, acid solution, complexing agent, and alkali solution on a poisoned catalyst was evaluated through experimental and theoretical calculations. For a Pb-poisoned catalyst, deionized water, acetic acid, and triethylenetetramine were used to wash. NO_x conversion rate on the Pb-V₂O₅-WO₃/TiO₂-SiO₂ catalyst increased from approximately 59.49% to 95.70%, which is 98.43% of the efficiency of the original fresh catalyst. As for an As-poisoned catalyst, deionized water, acetic acid solution, and sodium carbonate solution were used to wash, and the NO_x conversion rate on the As-V₂O₅-WO₃/TiO₂-SiO₂ catalyst increased from approximately 64.05% to 80.76%, which is 98.45% of the original efficiency of the fresh catalyst. The specific surface areas of the lead and arsenic regeneration catalyst were 46.41 m²/g and 45.95 m²/g respectively, approximately 14.00% and 11.02% higher than that of the poisoned catalyst (40.71 m²/g and 41.39 m²/g).The study provides a new method for the regeneration of SCR catalysts, which is particularly applicable for regenerating a large number of Pb- and As-poisoned catalysts.

Impact of primary NO2 emissions at different urban sites exceeding the European NO2 standard limit

A large part of the European population is still exposed to ambient nitrogen dioxide (NO₂) levels exceeding the European Union (EU) air quality standards, being a key challenge to reduce NO₂ concentrations across many European urban areas, particularly close to roads. In this work, a trend analysis of pollutants involved in NO₂ processes was done for the period 2003-2014 in traffic sites from three Spanish cities (Barcelona, Madrid and Granada) that still exceed the European NO₂ air quality standard limits. We also estimated the contributions of primary NO₂ emissions and photo-chemically formed NO₂ to the observed ambient NO₂ concentrations in order to explore their possible role in the observed NO₂ concentration trends. The NO_x and NO concentrations at these traffic sites showed significant decreasing trends during the period 2003-2014, especially at Barcelona (BAR_TR) and Madrid (MAD_TR) traffic stations. The NO₂ concentrations showed statistically significant downward trends at BAR_TR and MAD_TR and remained unchanged at Granada traffic station (GRA_TR) during the study period. Despite the significant decrease in NO₂ concentrations in BCN_TR and MAD_TR during the analysed period, the NO₂ concentrations observed over these sites still above the annual NO₂ standard limit of 40 μg m^-3 and, therefore, more efficient measures are still needed. Primary NO₂ emissions significantly influence NO₂ concentrations at the three analysed sites. However, as no drastic changes are expected in the after-exhaust treatment technology that can reduce primary NO₂ emissions to zero in the near future, only a substantial reduction in NO_x emissions will help to comply with the NO₂ European air quality standards. Reduction of 78%, 56% and 16% on NO_x emissions in Barcelona, Madrid and Granada were estimated to be necessary to comply with the NO₂ annual limit of 40 μg m^-3.

Measurement-based investigation of ozone deposition to vegetation under the effects of coastal and photochemical air pollution in the Eastern Mediterranean

Dry deposition of ozone (O₃) to vegetation is an important pathway for its removal from the troposphere, and it can lead to adverse effects in plants and changes in climate. However, our mechanistic understanding of O₃ dry deposition is insufficient to adequately account for it in global and regional models, primarily because this process is highly complicated by feedback mechanisms and sensitivity to specific characteristics of vegetative environment and atmospheric dynamics and composition. We hypothesized that measuring dry deposition of O₃ to vegetation near the Eastern Mediterranean (EM) coast, where large variations in meteorological conditions and photochemical air pollution frequently occur, would enable identifying the mechanisms controlling O₃ deposition to vegetation. Moreover, we have only limited knowledge of O₃ deposition to vegetation occurring near a coastline, under air pollution, or in the EM. This study investigated O₃ deposition to mixed Mediterranean vegetation between the summers of 2015 and 2017, 3.6 km away from the EM coast, using the eddy covariance technique to quantify vertical flux of O₃ and its partitioning to stomatal and non-stomatal flux, concurrent with nitrogen oxide (NO_x), sulfur dioxide and carbon monoxide. Surprisingly, nighttime O₃-deposition velocity (V_d) was smaller than daytime V_d by only ~20-37% on average for all measurement periods, primarily related to moderate nighttime atmospheric stability due to proximity to the seashore. We provide evidence for the role of sea-salt aerosols in enhancing O₃ deposition via surface-wetness buildup at low relative humidity near the coast, and for daytime enhancement of O₃ deposition by the combined effects of biogenic volatile organic compound emission and surface-wetness buildup. We further show that NO_x emitted from elevated emission sources can reduce O₃ deposition, and even lead to a positive O₃ flux, demonstrating the importance of adequately taking into account the impact of air pollution on O₃ deposition to vegetation.

Low NOx combustion and SCR flow field optimization in a low volatile coal fired boiler

Low NO_x burner redesign and deep air staging have been carried out to optimize the poor ignition and reduce the NO_x emissions in a low volatile coal fired 330 MW_e boiler. Residual swirling flow in the tangentially-fired furnace caused flue gas velocity deviations at furnace exit, leading to flow field unevenness in the SCR (selective catalytic reduction) system and poor denitrification efficiency. Numerical simulations on the velocity field in the SCR system were carried out to determine the optimal flow deflector arrangement to improve flow field uniformity of SCR system. Full-scale experiment was performed to investigate the effect of low NO_x combustion and SCR flow field optimization. Compared with the results before the optimization, the NO_x emissions at furnace exit decreased from 550 to 650 mg/Nm³ to 330-430 mg/Nm³. The sample standard deviation of the NO_x emissions at the outlet section of SCR decreased from 34.8 mg/Nm³ to 7.8 mg/Nm³. The consumption of liquid ammonia reduced from 150 to 200 kg/h to 100-150 kg/h after optimization.

Development of a new radial passive sampling device for atmospheric NOx determination

In this paper we used Na₂CO₃-impregnated silica as reactive substrate for the determination of atmospheric NO_x (NO+NO₂) by using a passive sampling device, with radial symmetry, which is unprecedented. We conducted laboratory and field tests at an urban setting, with co-located passive samplers and continuous measurements of NO_x by a chemiluminescence detector, used as reference. The performance of the carbonate-based sorbent for the NO_x sampler was evaluated in two different time frames (autumn 2016 and winter 2017), characterised by different environmental conditions. The comparison of the NO_x concentration levels measured by passive sampling, using Na₂CO₃ as NO_x sorbent, showed a close relationship with those obtained by the chemiluminescence analyzer. Validation experiments in the laboratory and in the field are reported together with the calculation of the diffusion-sampling rate of the samplers.

Real world CO2 and NOx emissions from 149 Euro 5 and 6 diesel, gasoline and hybrid passenger cars

In this study CO₂ and NO_x emissions from 149 Euro 5 and 6 diesel, gasoline and hybrid passenger cars were compared using a Portable Emissions Measurement System (PEMS). The models sampled accounted for 56% of all passenger cars sold in Europe in 2016. We found gasoline vehicles had CO₂ emissions 13-66% higher than diesel. During urban driving, the average CO₂ emission factor was 210.5 (sd. 47) gkm^-1 for gasoline and 170.2 (sd. 34) gkm^-1 for diesel. Half the gasoline vehicles tested were Gasoline Direct Injection (GDI). Euro 6 GDI engines <1.4ℓ delivered ~17% CO₂ reduction compared to Port Fuel Injection (PFI). Gasoline vehicles delivered an 86-96% reduction in NO_x emissions compared to diesel cars. The average urban NO_x emission from Euro 6 diesel vehicles 0.44 (sd. 0.44) gkm^-1 was 11 times higher than for gasoline 0.04 (sd. 0.04) gkm^-1. We also analysed two gasoline-electric hybrids which out-performed both gasoline and diesel for NO_x and CO₂. We conclude action is required to mitigate the public health risk created by excessive NO_x emissions from modern diesel vehicles. Replacing diesel with gasoline would incur a substantial CO₂ penalty, however greater uptake of hybrid vehicles would likely reduce both CO₂ and NO_x emissions. Discrimination of vehicles on the basis of Euro standard is arbitrary and incentives should promote vehicles with the lowest real-world emissions of both NO_x and CO₂.

The production of formaldehyde and hydroxyacetone in methacrolein photooxidation: New insights into mechanism and effects of water vapor

Methacrolein (MACR) is an abundant multifunctional carbonyl compound with high reactivity in the atmosphere. In this study, we investigated the hydroxyl radical initiated oxidation of MACR at various NO/MACR ratios (0 to 4.04) and relative humidities (<3% to 80%) using a flow tube. Meanwhile, a box model based on the Master Chemical Mechanism was performed to test our current understanding of the mechanism. In contrast to the reasonable predictions for hydroxyacetone production, the modeled yields of formaldehyde (HCHO) were twice higher than the experimental results. The discrepancy was ascribed to the existence of unconsidered non-HCHO forming channels in the chemistry of CH₃C(CH₂)OO, which account for approx. 50%. In addition, the production of hydroxyacetone and HCHO were affected by water vapor as well as the initial NO/MACR ratio. The yields of HCHO were higher under humid conditions than that under dry condition. The yields of hydroxyacetone were higher under humid conditions at low-NO_x level, while lower at high-NO_x level. The reasonable explanation for the lower hydroxyacetone yield under humid conditions at high-NO_x level is that water vapor promotes the production of methacrolein nitrate in the reaction of HOCH₂C(CH₃)(OO)CHO with NO due to the peroxy radical-water complex formation, which was evidenced by calculational results. And the minimum equilibrium constant of this water complex formation was estimated to be 1.89×10^-18cm³/molecule. These results provide new insights into the MACR oxidation mechanism and the effects of water vapor.

The selective catalytic reduction of NO over Ce0.3TiOx-supported metal oxide catalysts

A Ce_0.3TiO_x oxide carrier was synthesized via a sol-gel process, and Ce_0.3TiO_x supported metal (M=Cd, Mn, Fe, W, Mo) oxide catalysts were prepared by the method of incipient-wetness impregnation. The catalysts were characterized by means of X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), and Temperature-programmed reduction with H₂ (H₂-TPR). The catalytic activities for de-NO_x were evaluated by the NH₃-SCR reaction. Among all the catalysts tested, the 2wt.% Cd/Ce_0.3TiO_x catalyst exhibited the best NH₃-SCR performance, with a wide temperature window of 250-450°C for NO conversion above 90%. Moreover, the catalyst showed N₂ selectivity greater than 99% from 200 to 450°C.

NOx promotion of SO2 conversion to sulfate: An important mechanism for the occurrence of heavy haze during winter in Beijing

In this study, concentrations of NO_x, SO₂, O₃ and fine particles (PM_2.5) were measured at three monitoring stations in Beijing during 2015. For extreme haze episodes during 25 Nov. - 3 Dec. 2015, observation data confirmed that high concentrations of NO_x promoted the conversion of SO₂ to sulfate. Annual data confirmed that this is an important mechanism for the occurrence of heavy haze during winter in Beijing. Furthermore, in situ perturbation experiments in a potential aerosol mass (PAM) reactor were carried out at Shengtaizhongxin (STZX) station during both clean and polluted days. The concentrations of SO₄^2-, NH₄⁺, NO₃^- and organic aerosol were positively related to the concentration of added NO₂. These results provide definitive evidence that NO₂ can promote the conversion of SO₂ to sulfate. At the same time, we found that NO₂ can promote the formation of NH₄⁺ and organic compounds in the aerosols. Our results illustrate that strengthened controls of nitrogen oxides is a key step in reducing the fine particles level in China.

DNA methylation and exposure to ambient air pollution in two prospective cohorts

Long-term exposure to air pollution has been associated with several adverse health effects including cardiovascular, respiratory diseases and cancers. However, underlying molecular alterations remain to be further investigated. The aim of this study is to investigate the effects of long-term exposure to air pollutants on (a) average DNA methylation at functional regions and, (b) individual differentially methylated CpG sites. An assumption is that omic measurements, including the methylome, are more sensitive to low doses than hard health outcomes. This study included blood-derived DNA methylation (Illumina-HM450 methylation) for 454 Italian and 159 Dutch participants from the European Prospective Investigation into Cancer and Nutrition (EPIC). Long-term air pollution exposure levels, including NO2, NOx, PM2.5, PMcoarse, PM10, PM2.5 absorbance (soot) were estimated using models developed within the ESCAPE project, and back-extrapolated to the time of sampling when possible. We meta-analysed the associations between the air pollutants and global DNA methylation, methylation in functional regions and epigenome-wide methylation. CpG sites found differentially methylated with air pollution were further investigated for functional interpretation in an independent population (EnviroGenoMarkers project), where (N=613) participants had both methylation and gene expression data available. Exposure to NO2 was associated with a significant global somatic hypomethylation (p-value=0.014). Hypomethylation of CpG island's shores and shelves and gene bodies was significantly associated with higher exposures to NO2 and NOx. Meta-analysing the epigenome-wide findings of the 2 cohorts did not show genome-wide significant associations at single CpG site level. However, several significant CpG were found if the analyses were separated by countries. By regressing gene expression levels against methylation levels of the exposure-related CpG sites, we identified several significant CpG-transcript pairs and highlighted 5 enriched pathways for NO2 and 9 for NOx mainly related to the immune system and its regulation. Our findings support results on global hypomethylation associated with air pollution, and suggest that the shores and shelves of CpG islands and gene bodies are mostly affected by higher exposure to NO2 and NOx. Functional differences in the immune system were suggested by transcriptome analyses.

Photocatalytic removal of gaseous nitrogen oxides using WO3/TiO2 particles under visible light irradiation: Effect of surface modification

Photocatalytic nanoparticles have been receiving considerable attention for their potential use in many environmental management applications, including urban air quality control. This paper investigates the performance of surface modified WO₃/TiO₂ composite particles in removing gaseous nitrogen oxides (NO_x) under visible light irradiation. The WO₃/TiO₂ composite particles were synthesized using a modified wet chemical method with different concentrations of NaOH solution used as a surface modification agent for the host TiO₂ particles. The NO_x removal efficiency of the WO₃/TiO₂ particles was evaluated using a lab-scale continuous gas flow photo-reactor with a gas contact time of 1 min. Results showed that surface modification using NaOH can enhance the photocatalytic activity of the WO₃/TiO₂ particles. The NO_x removal efficiency of the surface modified WO₃/TiO₂ was greater than 90%, while that of WO₃/TiO₂ particles prepared by the conventional wet chemical method was ∼75%. The enhanced removal efficiency might be attributed to the formation of oxygen vacancies on the TiO₂ surface, providing sites for WO₃ particles to effectively bind with TiO₂. However, excess amount of NaOH >3 M deteriorated the photocatalytic performance due to the increased agglomeration of the host TiO₂ particles.

Characteristics of on-road NOx emissions from Euro 6 light-duty diesel vehicles using a portable emissions measurement system

This paper presents the on-road nitrogen oxides (NO_x) emissions measurements from Euro 6 light-duty diesel vehicles using a portable emissions measurement system on the predesigned test routes in the metropolitan area of Seoul, Korea. Six diesel vehicles were tested and the NO_x emissions results were analyzed according to the driving routes, driving conditions, data analysis methods, and ambient temperatures. Total NO_x emissions for route 1, which has higher driving severity than route 2, differed by -4-60% from those for route 2. The NO_x emissions when the air conditioner (AC) was used were higher by 68% and 85%, on average, for routes 1 and 2, respectively, compared to when the AC was not used. The analytical results for NO_x emissions by the moving averaging window method were higher by 2-31% compared to the power binning method. NO_x emissions at lower ambient temperatures (0-5°C) were higher by 82-192% compared to those at higher ambient temperatures (15-20°C). This result shows that performance improvements of exhaust gas recirculation and the NO_x after-treatment system will be needed at lower ambient temperatures.

A new sorbent tube for atmospheric NOx determination by active sampling

In this paper we used hydrated mayenite as reactive substrate for NO_x active sampling in the air, which is novel. The performance of the mayenite-based sorbent for the NO_x tubes was evaluated in two different monitoring surveys (autumn 2015 and winter 2016), characterized by different environmental conditions. Sorbent tubes filled with mayenite were exposed simultaneously to triethanolamine (TEA)-based sorbent tubes and to a chemiluminescence detector, as reference. The comparison of the NO_x concentration levels measured by active sampling, using mayenite as NO_x sorbent, showed a close relationship with the chemiluminescence analyzer. The effect of the environmental conditions on the performance of both mayenite and TEA-based sorbent tubes was evaluated and limitations connected to the use of TEA were discussed.

Overestimation of on-road air quality surveying data measured with a mobile laboratory caused by exhaust plumes of a vehicle ahead in dense traffic areas

The unintended influence of exhaust plumes emitted from a vehicle ahead to on-road air quality surveying data measured with a mobile laboratory (ML) at 20-40 km h^-1 in dense traffic areas was investigated by experiment and life-sized computational fluidic dynamics (CFD) simulation. The ML equipped with variable sampling inlets of five columns by four rows was used to measure the spatial distribution of CO₂ and NO_x concentrations when following 5-20 m behind a sport utility vehicle (SUV) as an emitter vehicle equipped with a portable emission monitoring system (PEMS). The PEMS measured exhaust gases at the tailpipe for input data of the CFD simulations. After the CFD method was verified with experimental results of the SUV, dispersion of exhaust plumes emitted from a bus and a sedan was numerically analyzed. More dilution of the exhaust plume was observed at higher vehicle speeds, probably because of eddy diffusion that was proportional to turbulent kinetic energy and vehicle speed. The CO₂ and NO_x concentrations behind the emitter vehicle showed less overestimation as both the distance between the two vehicles and their background concentrations increased. If the height of the ML inlet is lower than 2 m and the ML travels within 20 m behind a SUV and a sedan ahead at 20 km h^-1, the overestimation should be considered by as much as 200 ppb in NO_x and 80 ppm in CO₂. Following a bus should be avoided if possible, because effect of exhaust plumes from a bus ahead could not be negligible even when the distance between the bus and the ML with the inlet height of 2 m, was more than 40 m. Recommendations are provided to avoid the unintended influence of exhaust plumes from vehicles ahead of the ML during on-road measurement in urban dense traffic conditions.

Increase in ozone due to the use of biodiesel fuel rather than diesel fuel

The consumption of fuel by vehicles emits nitrogen oxides (NOx) and non-methane hydrocarbons (NMHCs) into the atmosphere, which are important ozone precursors. Ozone is formed as a secondary pollutant via photochemical processes and is not emitted directly into the atmosphere. In this paper, the ozone increase resulting from the use of biodiesel and diesel fuels was investigated, and the different ozone formation trends were experimentally evaluated. Known amounts of exhaust gas from a power generator operated using biodiesel and diesel fuels were added to ambient air. The quality of the ambient air, such as the initial NMHC and NOx concentrations, and the irradiation intensity have an effect on the ozone levels. When 30 cm(3) of biodiesel fuel exhaust gas (BFEG) or diesel fuel exhausted gas (DFEG) was added to 18 dm(3) of ambient air, the highest ratios of ozone increase from BFEG compared with DFEG in Japan and Vietnam were 31.2 and 42.8%, respectively, and the maximum ozone increases resulting from DFEG and BFEG compared with the ambient air in Japan were 17.4 and 26.4 ppb, respectively. The ozone increase resulting from the use of BFEG was large and significant compared to that from DFEG under all experimental conditions. The ozone concentration increased as the amount of added exhaust gas increased. The ozone increase from the Jatropha-BFEG was slightly higher than that from waste cooking oil-BFEG.

Catalytic decomposition of gaseous PCDD/Fs over V2O5/TiO2-CNTs catalyst: Effect of NO and NH3 addition

There is a strong need for a control technology that simultaneously achieving the abatement of PCDD/Fs (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans) and nitrogen oxides (NOx) emissions in waste incineration industry. TiO2 and carbon nanotubes (CNTs) were used as composite carriers to support vanadium oxide as an innovative catalyst to simultaneously control PCDD/Fs and NO emissions. The removal efficiencies (RE) of PCDD/Fs by V2O5/TiO2-CNTs catalyst under a space velocity (SV) of 20,000 h(-1) reaches 99.9% at 150 °C and adsorption is supposed to be the main mechanism at this temperature. The influence of NONH3 reaction on PCDD/Fs catalytic reaction is investigated. The kinetics analysis exhibits that the addition of NO and NH3 reduces the activation energies for OCDD (octachlorodibenzo-p-dioxin) and OCDF (octachlorodibenzofuran) decomposition to 3.6 kJ/mol and 5.4 kJ/mol respectively.

Effects of co-processing sewage sludge in cement kiln on NOx, NH3 and PAHs emissions

The effects of co-processing sewage sludge in cement kiln on NOx, NH3 and PAHs emissions were systematically investigated in a cement production line in Beijing. The results show that co-processing the sewage sludge was helpful to reduce NOx emission, which primarily depends on the NH3 amount released from the sewage sludge. Meanwhile, NOx and NH3 concentrations in the flue gas have a negative correlation, and the contribution of feeding the sewage sludge to NOx removal decreased with the increase of injection amount of ammonia water in the SNCR system. Therefore, it is suggested that the injection amount of ammonia water in SNCR system may reduce to cut down the operating costs during co-processing the sewage sludge in cement kiln. In addition, the emission of total PAHs seems to increase with the increased amount of the sewage sludge feeding to the cement kiln. However, the distributions of PAHs were barely changed, and lower molecular weight PAHs were mainly distributed in gaseous phase, accounted for the major portion of PAHs when co-processing sewage sludge in cement kiln.

Simultaneous measurements of on-road/in-vehicle nanoparticles and NOx while driving: Actual situations, passenger exposure and secondary formations

Simultaneous measurements of on-road and in-vehicle NO and NO2 levels, particle number concentrations (PNCs), and particles size distributions were performed while driving using a test vehicle equipped with real-time sensors. The results obtained on regional roads showed that heavy-duty vehicles in traffic seem to have a major impact on on-road air quality. Measurements on highways that included a 10km tunnel and a 2km uphill section of road indicated that sub-50nm particles have different features from the other species because of their higher volatility. The other species showed quite high on-road concentrations in the tunnel. In-vehicle conditions were made similar to the on-road ones by setting the air conditioning (AC) mode to the fresh air mode. The in-vehicle NO2 concentration in the tunnel was over 0.50ppmV, which is almost five times higher than the 1-hour ambient air quality standard proposed by the World Health Organization (WHO). In sections other than the tunnel, the in-vehicle NO2 concentration was almost the same as the 1-hour WHO standard. Higher on-road NO2/NOx ratios than those of exhaust gases and different behavior of sub-50nm particles from other species suggested that NO2 and sub-50nm particles were mainly due to secondary products formed by atmospheric reactions.

Source apportionment and health effect of NOx over the Pearl River Delta region in southern China

As one of the most notorious atmospheric pollutants, NOx not only promotes the formation of ozone but also has adverse health effects on humans. It is therefore of great importance to study the sources of NOx and its effects on human health. The Comprehensive Air Quality Model (CAMx) modeling system and ozone source apportionment technology (OSAT) were used to study the contribution of NOx from different emission sources over southern China. The results indicate that heavy duty diesel vehicles (HDDVs) and industrial point sources are the two major local NOx sources, accounting for 30.8% and 18.5% of local NOx sources, respectively. In Hong Kong, marine emissions contributed around 43.4% of local NOx in 2011. Regional transport is another important source of this pollutant, especially in February and November, and it can contribute over 30% of ambient NOx on average. Power plant point emission is an significant regional source in Zhuhai, Zhongshan and Foshan. The total emission sources are estimated to cause 2119 (0-4405) respiratory deaths and 991 (0-2281) lung cancer deaths due to long-term exposure to NOx in the Pearl River Delta region. Our results suggest that local governments should combine their efforts and vigorously promote further reduction of NOx emissions, especially for those sources that make a substantial contribution to NOx emissions and affect human health: HDDV, LDGV, industrial point sources and marine sources.

Passive samplers and community science in regional air quality measurement, education and communication

Charlotte, in Mecklenburg County, North Carolina, was ranked in the top ten cities with the worst air quality for ozone in the United States by the American Lung Association from 2009 to 2011. Nearby counties that may experience similar air quality do not have state or county monitors. This study utilized NOx and ozone Ogawa passive samplers and community scientists to monitor air quality in five counties surrounding Charlotte and increase public engagement in air quality issues. Community scientists deployed samplers weekly at a residential site within each county. Samples were analyzed using spectrophotometry and ion chromatography. Elevated NOx concentrations were observed in four of the five counties relative to those with existing monitors. Ozone concentrations showed little county to county variation, except Iredell and Cabarrus which had higher concentrations than Rowan. Community involvement in this work led to an increase in local dissemination of the results, thus increasing air quality awareness.

Simultaneous removal of PCDD/Fs and NOx from the flue gas of a municipal solid waste incinerator with a pilot plant

The pilot-scale plant on the simultaneous removal of PCDD/Fs and NOx from the flue gas of a municipal solid waste incinerator is presented. In order to research the influence of temperature on the catalytic decomposition of PCDD/Fs and the selective catalytic reduction of NOx, the experiments were performed at 220 °C, 260 °C, and 300 °C, and the congener profiles of PCDD/Fs for the samples collected at the inlet and outlet were illustrated. Noteworthy, the detailed congener distributions of PCDD/Fs in the gas-phase and particle-phase of the inlet and 300-outlet (decomposition temperature = 300 °C) samples are presented, and the removal efficiencies η(g-I-TEQ) and η(p-I-TEQ) reached to 94.94% and 99.67%, respectively. The effect of the SCR process on the removal of PCDD/Fs was also studied at a relatively low temperature of 220 °C. Additionally, the NOx emissions and the SCR efficiencies were investigated.

Simultaneous suppression of PCDD/F and NO(x) during municipal solid waste incineration

Thiourea was tested as a dioxins inhibitor in a full-scale municipal solid waste incinerator with high capacity (34 t h(-1)). The suppressant, featuring a high S- and N-content, was converted into liquor and then injected (35 kg h(-1)) into the furnace (850 °C) through the inlets already used for Selective Non-Catalytic Reduction (SNCR) of flue gas NOx. The first results show that thiourea reduces the dioxins in flue gas by 55.8 wt.%, those in fly ash by 90.3 wt.% and the total dioxins emission factor by 91.0 wt.%. The concentration of PCDD/Fs was 0.08 ng TEQ Nm(-3), below the national standard of 0.1 ng TEQ Nm(-3). The weight average chlorination degree of dioxins decreases slightly after adding the inhibitor, indicating that it suppresses both the formation and the chlorination of dioxins. Analysis of fly ash by scanning electron microscope (SEM) suggests that the particle size becomes larger after adding the inhibitor. Further analysis using an energy dispersive spectrometer (EDS) reveals that the sulphur content in fly ash rises, but the chlorine content declines when adding thiourea. These results suggest that poisoning the metal catalyst and blocking the chlorination are probably responsible for suppression. NOx reduction attains 42.6 wt.%. These tests are paving the way for further industrial application and assist in controlling the future emissions of dioxins and NOx from MSWI.

2001-2012 trends on air quality in Spain

This study aims at interpreting the 2001-2012 trends of major air pollutants in Spain, with a major focus on evaluating their relationship with those of the national emission inventories (NEI) and policy actions. Marked downward concentration trends were evidenced for PM10, PM2.5 and CO. Concentrations of NO2 and NOx also declined but in a lesser proportion at rural and traffic sites. At rural sites O3 has been kept constant, whereas it clearly increased at urban and industrial sites. Comparison of the air quality trends and major inflection points with those from NEIs, the National Energy Consumption and the calendar of the implementation of major policy actions allowed us to clearly identify major benefits of European directives on power generation and industrial sources (such as the Large Combustion Plants and the Integrated Pollution Prevention and Control Directives). This, together with a sharp 2007-2008 decrease of coal consumption has probably caused the marked parallel decline of SO2, NOx and for PM2.5 concentrations. Also the effect of the EURO 4 and 5 vehicle emission standards on decreasing emissions of PM and CO from vehicles is noticeable. The smooth decline in NO2-NOx levels is mostly attributed to the low efficiency of EURO 4 and 5 standards in reducing real life urban driving NO2 emissions. The low NOx decrease together with the complexity of the reactions of O3 formation is responsible for the constant O3 concentrations, or even the urban increase. The financial crisis has also contributed to the decrease of the ambient concentration of pollutants; however this caused a major reduction of the primary energy consumption from 2008 to 2009, and not from 2007 to 2008 when ambient air PM and SO2 sharply decreased. The meteorological influence was characterized by a 2008-2012 period favorable to the dispersion of pollutants when compared to the 2001-2007.

Compliance of Royal Naval ships with nitrogen oxide emissions legislation

Nitrogen oxide (NOx) emissions from marine diesel engines pose a hazard to human health and the environment. From 2021, demanding emissions limits are expected to be applied to sea areas that the Royal Navy (RN) accesses. We analyze how these future constraints affect the choice of NOx abatement systems for RN ships, which are subject to more design constraints than civilian ships. A weighted matrix approach is used to facilitate a quantitative assessment. For most warships to be built soon after 2021 Lean Nitrogen Traps (LNT) in conjunction with Exhaust Gas Recirculation (EGR) represents a relatively achievable option with fewer drawbacks than other system types. Urea-selective catalytic reduction is likely to be most appropriate for ships that are built to civilian standards. The future technologies that are at an early stage of development are discussed.