Fighting global warming: The potential of photocatalysis against CO2, CH4, N2O, CFCs, tropospheric O3, BC and other major contributors to climate change

Nitration-Promoted Vanadate Catalysts for Low-Temperature Selective Catalytic Reduction of NOX with NH3

Vanadium-based catalysts have been commercially used in selective catalytic reduction (SCR), owing to their high catalytic activity and effectiveness across a wide temperature range; however, their catalytic efficiency decreases at lower temperatures under exposure to SOX. This decrease is largely due to ammonium sulfate generation on the catalyst surface. To overcome this limitation, we added ammonium nitrate to the V2O5-WO3/TiO2 catalyst, producing a V2O5-WO3/TiO2 catalyst with nitrate functional groups. With this approach, we found that it was possible to adjust the amount of these functional groups by varying the amount of ammonium nitrate. Overall, the resultant nitrate V2O5-WO3/TiO2 catalyst has large quantities of NO3- and chemisorbed oxygen, which improves the density of Brønsted and Lewis acid sites on the catalyst surface. Furthermore, the nitrated V2O5-WO3/TiO2 catalyst has a high NOX removal efficiency and N2 selectivity at low temperatures (i.e., 300 °C); this is because NO3- and chemisorbed oxygen, generated by nitrate treatment, facilitated the occurrence of a fast SCR reaction. The approach outlined in this study can be applied to a wide range of SCR catalysts, allowing for the development of more, low-temperature SCR catalysts.

Fast and slow responses of surface air temperature in China to short-lived climate forcers

Short-lived climate forcers (SLCFs), including aerosols, tropospheric ozone, and methane in this work, are attracting increasing attention because of their extensive impacts on regional climate and air pollution. To clarify the impact of controlling SLCFs in high-emission areas on regional surface air temperature (SAT), we quantified the SAT response in China due to both global and China's SLCF changes by using an aerosol-climate model. The average SAT response in China to global SLCF changes from 1850 to 2014 was -2.53 °C ± 0.52 °C, which was much stronger than the global mean SAT response (-1.85 °C ± 0.15 °C). There are two cooling centers in China, located in the northwest inland areas (NW) and southeastern areas (SE), with area mean SAT responses of -3.39 °C ± 0.70 °C and -2.43 °C ± 0.62 °C, respectively. Because the SE area has experienced greater changes in SLCFs concentrations, compared with the NW area, China's SLCFs contribute more to the SAT response in the SE (approximately 42 %) than to the SAT response in the NW (<25 %). We divided the SAT response into fast and slow components to investigate the underlying mechanisms. In the fast response, the strength of the regional SAT response was closely connected to changes in the SLCFs concentration. The prominent increase in SLCFs in the SE area reduced the surface net radiation flux (NRF), thereby decreasing the SAT by 0.44 °C ± 0.47 °C. The smaller increase in SLCFs in the NW area, compared with the SE area, resulted in a less reduction in NRF and a minor fast SAT response (-0.01 °C ± 0.76 °C). In the slow response, the SLCFs-induced increases of mid- and low-cloud cover significantly reduced the NRF, resulting in strong slow SAT responses of -3.38 °C ± 0.70 °C and -1.98 °C ± 0.62 °C in the NW and SE areas, respectively.

Crosscutting of the pollutants and building ventilation systems: a literature review

Considering the time spent in enclosed environments, it is essential to study the relationship between pollutants and building ventilation systems to find whether the types and levels of pollutants and greenhouse gasses, which are expected to be exhaled through ventilation systems into the atmosphere, have been adequately evaluated. We propose the hypothesis that the exhaled air from residential buildings contains pollutants that may become another source of contamination affecting urban air quality and potentially contributing to climate drivers. Thus, the main goal of this article is to present a cross-review of the identification of pollutants expected to be exhaled through ventilation systems in residential buildings. This approach has created the concept of "exhalation of buildings" a new concept enclosed within the research project in which this article is included. We analyze the studies related to the most significant pollutants found in buildings and the studies about the relation of buildings' ventilation systems with such pollutants. Our results show that, on the one hand, the increase in the use of mechanical ventilation systems in residential buildings has been demonstrated to enhance the ventilation rate and generally improve the indoor air quality conditions. But no knowledge could be extracted about the corresponding environmental cost of this improvement, as no systematic data were found about the total mass of contaminants exhaled by those ventilation systems. At the same time, no projects were found that showed a quantitative study on exhalation from buildings, contrary to the existence of studies on pollutants in indoor air.

Metal-Organic Frameworks for Greenhouse Gas Applications

Using petrol to supply energy for a car or burning coal to heat a building generates plenty of greenhouse gas (GHG) emissions, including carbon dioxide (CO₂ ), water vapor (H₂ O), methane (CH₄ ), nitrous oxide (N₂ O), ozone (O₃ ), fluorinated gases. These up-and-coming metal-organic frameworks (MOFs) are structurally endowed with rigid inorganic nodes and versatile organic linkers, which have been extensively used in the GHG-related applications to improve the lives and protect the environment. Porous MOF materials and their derivatives have been demonstrated to be competitive and promising candidates for GHG separation, storage and conversions as they shows facile preparation, large porosity, adjustable nanostructure, abundant topology, and tunable physicochemical property. Enormous progress has been made in GHG storage and separation intrinsically stemmed from the different interaction between guest molecule and host framework from MOF itself in the recent five years. Meanwhile, the use of porous MOF materials to transform GHG and the influence of external conditions on the adsorption performance of MOFs for GHG are also enclosed. In this review, it is also highlighted that the existing challenges and future directions are discussed and envisioned in the rational design, facile synthesis and comprehensive utilization of MOFs and their derivatives for practical applications.

Photocatalytic soot degradation under UV and visible light

Particulate matter is one of the most persistent global air pollutants that is causing health problems, climate disturbance and building deterioration. A sustainable technique that is able to degrade soot using (sun)light is photocatalysis. Currently, research on photocatalytic soot oxidation focusses on large band gap TiO₂-based photocatalysts and thus requires the use of UV light. It would prove useful if visible light, and thus a larger fraction of the (freely available) solar spectrum, could additionally be utilised to drive this process. In this work, a visible light-active photocatalyst, WO₃, is benchmarked to TiO₂ under both UV and visible light. At the same time, the versatility and drastic improvement of a recently introduced digital image-based soot degradation detection method are demonstrated. An additional step correcting for non-soot related catalyst colour changes is applied, resulting in accurate detection and quantification of soot degradation for all studied photocatalysts, even for materials such as WO₃ that are inherently coloured. With this study, we aim to broaden the scope of photocatalytic soot oxidation technology to visible light-active photocatalyst. Along with this study, we provide a versatile soot degradation detection methodology based on digital image analysis that is made widely applicable.

Anodic TiO2 Nanotube Layers for Wastewater and Air Treatments: Assessment of Performance Using Sulfamethoxazole Degradation and N2O Reduction

The preparation of anodic TiO₂ nanotube layers has been performed using electrochemical anodization of Ti foil for 4 h at different voltages (from 0 V to 80 V). In addition, a TiO₂ thin layer has been also prepared using the sol-gel method. All the photocatalysts have been characterized by XRD, SEM, and DRS to investigate the crystalline phase composition, the surface morphology, and the optical properties, respectively. The performance of the photocatalyst has been assessed in versatile photocatalytic reactions including the reduction of N₂O gas and the oxidation of aqueous sulfamethoxazole. Due to their high specific surface area and excellent charge carriers transport, anodic TiO₂ nanotube layers have exhibited the highest N₂O conversion rate (up to 10% after 22 h) and the highest degradation extent of sulfamethoxazole (about 65% after 4 h) under UVA light. The degradation mechanism of sulfamethoxazole has been investigated by analyzing its transformation products by LC-MS and the predominant role of hydroxyl radicals has been confirmed. Finally, the efficiency of the anodic TiO₂ nanotube layer has been tested in real wastewater reaching up to 45% of sulfamethoxazole degradation after 4 h.

Recent advancement in conjugated polymers based photocatalytic technology for air pollutants abatement: Cases of CO2, NOx, and VOCs

According to World Health Organization (WHO) survey, air pollution has become the major reason of several fatal diseases, which had led to the death of 7 million peoples around the globe. The 9 people out of 10 breathe air, which exceeds WHO recommendations. Several strategies are in practice to reduce the emission of pollutants into the air, and also strict industrial, scientific, and health recommendations to use sustainable green technologies to reduce the emission of contaminants into the air. Photocatalysis technology recently has been raised as a green technology to be in practice towards the removal of air pollutants. The scientific community has passed a long pathway to develop such technology from the material, and reactor points of view. Many classes of photoactive materials have been suggested to achieve such a target. In this context, the contribution of conjugated polymers (CPs), and their modification with some common inorganic semiconductors as novel photocatalysts, has never been addressed in literature till now for said application, and is critically evaluated in this review. As we know that CPs have unique characteristics compared to inorganic semiconductors, because of their conductivity, excellent light response, good sorption ability, better redox charge generation, and separation along with a delocalized π-electrons system. The advances in photocatalytic removal/reduction of three primary air-polluting compounds such as CO₂, NO_X, and VOCs using CPs based photocatalysts are discussed in detail. Furthermore, the synergetic effects, obtained in CPs after combining with inorganic semiconductors are also comprehensively summarized in this review. However, such a combined system, on to better charges generation and separation, may make the Adsorb & Shuttle process into action, wherein, CPs may play the sorbing area. And, we hope that, the critical discussion on the further enhancement of photoactivity and future recommendations will open the doors for up-to-date technology transfer in modern research.

Understanding ammonia and nitrous oxide formation in typical three-way catalysis during the catalyst warm-up period

Ammonia (NH₃) and nitrous oxide (N₂O) have been regarded as the typical secondary pollutants emitted from vehicles equipped with a three-way catalyst (TWC). MultiGas FT-IR Analyzer was applied to determine the outlet gas concentrations in the light-off experiments, in order to understand how different reaction conditions and catalyst aging affect the production of these two pollutants. It was found that N₂O formation is favored by the existence of excess oxygen during NO reduction, whereas NH₃ is readily formed within the lack of reactive oxygen species. Interestingly, the reduction of NO by H₂ in presence of excess oxygen can also lead to NH₃ formation when the active metal particles are large enough, which provides the rational explanation why the increased NH₃ was emitted from older gasoline vehicles. The loss of the catalytically active sites and reducibility caused by thermal aging requires longer time to warm-up thereby favors the N₂O and NH₃ formation, which is the major reason for the higher CO, NOx, HC, N₂O and NH₃ emissions from the old gasoline vehicles than that of low-mileage gasoline vehicles.

Effectiveness of an air cleaner device in reducing aerosol numbers and airborne bacteria from an enclosed type dairy barn

There is growing pressure to find technically feasible and economically viable solutions in reducing emissions of pollutants from various occupational settings to minimise environmental pollution. Hence, it is essential to develop and test methods for controlling pollutants from occupational backgrounds. We have tested an air cleaner device in reducing aerosol numbers by filtration and airborne bacteria by photocatalysis from an enclosed type dairy barn. Here, we had shown a significant reduction of larger size aerosol numbers (2.0-10.0 µm) and airborne total aerobic bacteria and Staphylococcus aureus (S. aureus) and complete clearance of Escherichia coli (E. coli) in the exhaust air of the air cleaner device. A greater 8.05% and 61.56% reduction of 5.0-10.0 µm aerosol numbers and airborne E. coli, respectively, were observed in the instantly treated central air of the dairy barn. We had found an increasing trend of aerosol numbers and airborne bacteria concentrations in the central air of the dairy barn after stopping the air cleaner device. We also had observed increased bacterial load in the filter paper of the air treatment chamber of the air cleaner device with the advancement of cleaning time. These findings are essential to validate air cleanings from various types of dairy microenvironments.

Mechanistic study on reduction of nitric oxide to nitrous oxide using a dicopper complex

A density functional theory study was carried out to investigate the reduction mechanisms of NO to N₂O using a dicopper complex reported by Zhang and coworkers (J. Am. Chem. Soc., 2019, 141, 10159-10164). The reaction mechanism consists of three steps: N-N bond formation, isomerization of the resultant N₂O₂ moiety, and cleavage of the N-O bond.

Feasibility of Solar Updraft Towers as Photocatalytic Reactors for Removal of Atmospheric Methane-The Role of Catalysts and Rate Limiting Steps

Due to the alarming speed of global warming, greenhouse gas removal from atmosphere will be absolutely necessary in the coming decades. Methane is the second most harmful greenhouse gas in the atmosphere. There is an emerging technology proposed to incorporating photocatalysis with solar updraft Towers (SUT) to remove methane from the air at a planetary scale. In this study, we present a deep analysis by calculating the potential of methane removal in relation to the dimensions and configuration of SUT using different photocatalysts. The analysis shows that the methane removal rate increases with the SUT dimensions and can be enhanced by changing the configuration design. More importantly, the low methane removal rate on conventional TiO₂ photocatalyst can be significantly improved to, for example, 42.5% on a more effective Ag-doped ZnO photocatalyst in a 200 MW SUT while the photocatalytic reaction is the rate limiting step. The factors that may further affect the removal of methane, such as more efficient photocatalysts, night operation and reaction zone are discussed as possible solutions to further improve the system.

A Review of Photocatalytic Materials for Urban NOx Remediation

NOx is a pervasive pollutant in urban environments. This review assesses the current state of the art of photocatalytic oxidation materials, designed for the abatement of nitrogen oxides (NOx) in the urban environment, and typically, but not exclusively based on titanium dioxide (TiO2). Field trials with existing commercial materials, such as paints, asphalt and concrete, in a range of environments including street canyons, car parks, tunnels, highways and open streets, are considered in-depth. Lab studies containing the most recent developments in the photocatalytic materials are also summarised, as well as studies investigating the impact of physical parameters on their efficiency. It is concluded that this technology may be useful as a part of the measures used to lower urban air pollution levels, yielding ∼2% NOx removal in the immediate area around the surface, for optimised TiO2, in some cases, but is not capable of the reported high NOx removal efficiencies >20% in outdoor urban environments, and can in some cases lower air quality by releasing hazardous by-products. However, research into new material is ongoing. The reason for the mixed results in the studies reviewed, and massive range of removal efficiencies reported (from negligible and up to >80%) is mainly the large range of testing practices used. Before deployment in individual environments site-specific testing should be performed, and new standards for lab and field testing should be developed. The longevity of the materials and their potential for producing hazardous by-products should also be considered.

Next City: Learning from Cities during COVID-19 to Tackle Climate Change

Fundamental principles of modern cities and urban planning are challenged during the COVID-19 pandemic, such as the advantages of large city size, high density, mass transport, free use of public space, unrestricted individual mobility in cities. These principles shaped the development of cities and metropolitan areas for more than a century, but currently, there are signs that they have turned from advantage to liability. Cities Public authorities and private organisations responded to the COVID-19 crisis with a variety of policies and business practices. These countermeasures codify a valuable experience and can offer lessons about how cities can tackle another grand challenge, this of climate change. Do the measures taken during the COVID-19 crisis represent a temporal adjustment to the current health crisis? Or do they open new ways towards a new type of urban development more effective in times of environmental and health crises? We address these questions through literature review and three case studies that review policies and practices for the transformation of city ecosystems mostly affected by the COVID-19 pandemic: (a) the central business district, (b) the transport ecosystem, and (c) the tourism–hospitality ecosystem. We assess whether the measures implemented in these ecosystems shape new policy and planning models for higher readiness of cities towards grand challenges, and how, based on this experience, cities should be organized to tackle the grand challenge of environmental sustainability and climate change.

Urban Ground-Level O3 Trends: Lessons from Portuguese Cities, 2010–2018

Big datasets of air-quality pollutants and weather data allow us to review trends of NO2, NO, O3, and global radiation (GR), for Lisbon, Porto and Coimbra, with regard to the historical period of 2010–2018. GR is expected to have a considerable impact on photochemical reactions of the O3 formation mechanism. We aim to characterize daily, monthly, and yearly trends. We explore Weekday (WD) versus weekend (WE), and seasonality of O3 and NO2. We are interested to know these pollutant peak concentration variations over the years and investigate if parallels can be drawn between urban mobility indicators and these pollutants. For this purpose, economic data, European emission standards, and car stock data (fuel, age, and number of vehicles) are cross-analyzed. How are they correlated? Has it impacted NO2 and O3 variations? How do different air-quality monitoring stations (AQMS), traffic and non-traffic, compare? How is Lisbon NOx-O3 correlated? What are its implications for future scenarios? Results show that urban mobility trends and economic events are correlated with NO2 and O3 variability. Weekend effect has a partial relationship with urban mobility trends and economy as it is relatively well correlated for Lisbon but not for Porto and Coimbra. Nonetheless, weekend effect for the period of 2010–2018 is overall trending upwards for all cities. In Lisbon and Coimbra, O3 concentrations also trend upwards during the same 2010–2018 period but for Porto they do not. Regardless, for the period of 2015–2018, after the economic recession, the upwards trends of both weekend effect and overall O3 concentrations are clear for all AQMS. For AQMS peak values comparison, Lisbon traffic AQMS registered an annual averaged 8-hour daily max O3 concentration of 34.4 ppb while Lisbon non-traffic AQMS presented 39.1 ppb. Altogether, annual 8-hour daily maximum values for 2010–2018 traffic AQMS in Lisbon show an inverse relationship with fuel sales, and have concentrations fluctuating between 28–35 ppb, which is slightly higher than the 2001–2010 historical European range of 27–31 ppb. Lastly, for the 8 years data in Lisbon, it has been shown that a negative NOx-O3 correlation exists, and the study location might be VOC–sensitive. This means that as NOx concentrations decrease, O3 concentrations become exponentially higher. Further research into VOCs with better data availability is required to make more concise claims. Regardless, it can be inferred that in a future scenario where mitigation continues to escalate, through O3 emission standards and an aggressive shift of car stock to electric vehicles, achieving unprecedented rises in O3 concentrations could be observed.

Properties of Iron-Modified-by-Silver Supported on Mordenite as Catalysts for NOx Reduction

A series of mono and bimetallic catalysts based on a Fe-Ag mixture deposited on mordenite was prepared by ion-exchange and evaluated in the catalytic activity test of the de-NOx reaction in the presence of CO/C3H6. The activity results showed that the most active samples were the Fe-containing ones, and at high temperatures, a co-promoter effect of Ag on the activity of Fe catalysts was also observed. The influence of the order of cation deposition on catalysts formation and their physicochemical properties was studied by FTIR (Fourier Transform Infrared Spectroscopy) of adsorbed NO, XANES (X-ray Absorption Near-Edge Structure), and EXAFS (Extended X-ray Absorption Fine Structure) and discussed in terms of the state of iron. Results of Fe K-edge XANES oscillations showed that, in FeMOR catalysts, iron was present in a disordered state as Fe3+ and Fe2+. In FeAgMOR, the prevailing species was Fe3+, while in the AgFeMOR catalyst, the state of iron was intermediate or mixed between FeMOR and FeAgMOR. The Fe K-edge EXAFS results were characteristic of a disordered phase, the first coordination sphere being asymmetric with two different Fe-O distances. In FeAgMOR and AgFeMOR, coordination of Fe-O was similar to Fe2O3 with a few amount of Fe2+ species. We may conclude that, in the bimetallic FeAgMOR and AgFeMOR samples, a certain amount of tetrahedral Al3+ ions in the mordenite framework is replaced by Fe3+ ions, confirming the previous reports that these species are active sites for the de-NOx reaction. Based on the thermodynamic analysis and experimental data, also, it was confirmed that the order of deposition of the components influenced the mechanism of active sites’ formation during the two steps ion-exchange synthesis.

Revealing the Effect of Nickel Particle Size on Carbon Formation Type in the Methane Decomposition Reaction

Carbon species deposition is recognized as the primary cause of catalyst deactivation for hydrocarbon cracking and reforming reactions. Exploring the formation mechanism and influencing factors for carbon deposits is crucial for the design of rational catalysts. In this work, a series of NixMgyAl-800 catalysts with nickel particles of varying mean sizes between 13.2 and 25.4 nm were obtained by co-precipitation method. These catalysts showed different deactivation behaviors in the catalytic decomposition of methane (CDM) reaction and the deactivation rate of catalysts increased with the decrease in nickel particle size. Employing TG-MS and TEM characterizations, we found that carbon nanotubes which could keep catalyst activity were more prone to form on large nickel particles, while encapsulated carbon species that led to deactivation were inclined to deposit on small particles. Supported by DFT calculations, we proposed the insufficient supply of carbon atoms and rapid nucleation of carbon precursors caused by the lesser terrace/step ratio on smaller nickel particles, compared with large particles, inhibit the formation of carbon nanotube, leading to the formation of encapsulated carbon species. The findings in this work may provide guidance for the rational design of nickel-based catalysts for CDM and other methane conversion reactions.

Microwave-Assisted Synthesis of Cobalt Oxide/Reduced Graphene Oxide (Co3O4–rGo) Composite and its Sulfite Enhanced Photocatalytic Degradation of Organic Dyes

One-pot synthesis of Co3O4 nanocrystals on reduced graphene oxide (rGO) was carried out by reacting cobalt nitrate, L-arginine, extract of Laportae aestuans as oxidant, fuel and reducing agent, respectively, in a domestic microwave. Morphologies of Co3O4–rGo (RGCO) composite was elucidated using UV-Vis, FT-IR, TEM, SEM, EDX, XRD and photoluminescence spectroscopies. The synthesized RGCO composite was applied as heterogeneous photocatalyst in the activation of Na2SO3 (sulfite) as sacrificial agent to degrade cationic dyes: rhodamine B (RhB) and methylene blue (MB), under visible light, at neutral pH 7.0. Photocatalytic performance of as-prepared RGCO was significantly enhanced in the presence of Na2SO3. Enhanced photocatalytic activity of RGCO was attributed to the synergistic effects between sulfite radicals generated in situ, and reduced graphene oxide, in which rGO served as electron sink to suppress recombination of photogenerated charge carriers. Plausible mechanistic pathways responsible for the activation of sulfite anions in situ are presented in this paper.

In situ evaluation of the NOx removal efficiency of photocatalytic pavements: statistical analysis of the relevance of exposure time and environmental variables

In the recent past, the NO_x removal efficiency of photocatalytic materials has been subject of many studies with promising results. However, many of these studies involve laboratory tests carried out under standardized climatic exposure conditions, often not representative of the real-world environment. With the aim to bridge this gap, selected photocatalytic materials have been applied to different substrates in outdoor demonstrator platforms at pilot scale as part of the project LIFE-PHOTOSCALING. The paper presents the results of in situ measurements of NO_x removal efficiency of the materials, performed during 17 months. Statistical models accounting for the influence of exposure time and relevant environmental variables are derived. They suggest that photocatalytic emulsions on the tested asphalt experience a significant loss of activity over time irrespective of climatic conditions. The efficiency of photocatalytic slurries on asphalt and of concrete tiles, with the photocatalyst applied on surface or in bulk, mainly depends on substrate humidity.

Copper(I) Complex Mediated Nitric Oxide Reductive Coupling: Ligand Hydrogen Bonding Derived Proton Transfer Promotes N2O(g) Release

A cuprous chelate bearing a secondary sphere hydrogen bonding functionality, [(PV-tmpa)Cu^I]⁺, transforms ^•NO_(g) to N₂O_(g) in high-yields in methanol. Ligand derived proton transfer facilitates N-O bond cleavage of a putative hyponitrite intermediate releasing N₂O_(g), underscoring the crucial balance between H-bonding capabilities and acidities in (bio)chemical ^•NO_(g) coupling systems.

Theoretical studies of infrared spectra for the N2-N2O complex: The tunneling effects of fundamental and combination bands

This study is a continuation of our previously published research for the N₂-N₂O complex [Journal of Chemical Physics 143 (2015) 154304], and focuses on predicting the quantum tunneling effects of infrared fundamental and combination bands. A new four-dimensional intermolecular potential energy surface (PES) was constructed for the vibrational excited state upon the N₂O ν₁ excitation at the same calculated level with the previous PES of ground state. Compared with the ground state, two equivalent T-shaped global minima are found to be slightly different in both structural parameters and binding energies. Based on the PESs of ground and vibrational excited states, the vibrational shift of infrared spectrum for the fundamental band in the N₂O ν₁ region is determined to be a blue shift of 1.29 cm^-1 for ¹⁴N₂-N₂O, which is in qualitative agreement with the experimentally observed value of 2.233 cm^-1 [Journal of Chemical Physics 140 (2014) 044332]. Furthermore, for the fundamental and disrotation bands, the calculated tunneling splitting is almost the same for the ground and vibrational excited states, so the tunneling effects cannot be observed for these bands using the infrared spectroscopic technique. Nevertheless for the infrared combination bands, our calculated results suggest that the tunneling effects for the torsion and twice disrotation bands are significantly larger, and the predicted infrared spectra display obvious differences for the different sub-states. If the sensitivity of infrared spectrometer is high enough, it is interesting to investigate the quantum tunneling effects experimentally.

Aggravating O3 pollution due to NOx emission control in eastern China

During the past five years, China has witnessed a rapid drop of nitrogen oxides (NO_x) owing to the wildly-applied rigorous emission control strategies across the country. However, ozone (O₃) pollution was found to steadily deteriorate in most part of eastern China, especially in developed regions such as Jing-Jin-Ji (JJJ), Yangtze River Delta region (YRD) and Pearl River Delta region (PRD). To shed more light on current O₃ pollution and its responses to precursor emissions, we integrate satellite retrievals, ground-based measurements together with regional numerical simulation in this study. It is indicated by multiple sets of observational data that NO_x in eastern China has declined more than 25% from 2012 to 2016. Based on chemical transport modeling, we find that O₃ formation in eastern China has changed from volatile organic compounds (VOCs) sensitive regime to the mixed sensitive regime due to NO_x reductions, substantially contributing to the recent increasing trend in urban O₃. In addition, such transitions tend to bring about an ~1-1.5 h earlier peak of net O₃ formation rate. We further studied the O₃ precursors relationships by conducting tens of sensitivity simulations to explore potential ways for effective O₃ mitigation. It is suggested that the past control measures that only focused on NO_x may not work or even aggravate O₃ pollution in the city clusters. In practice, O₃ pollution in the three regions is expected to be effectively mitigated only when the reduction ratio of VOCs/NO_x is greater than 2:1, indicating VOCs-targeted control is a more practical and feasible way.

Revealing the environmental pollution in nexus of aviation transportation in SAARC region

The environmental degradation has put serious concern among the nations at global level, yet contented measures are still lagged behind the prospective outcomes. This study is aimed at analyzing the existence of "aviation transportation Kuznets curve" together with "environmental Kuznets curve" in perspective of greenhouse gas (GHG) emissions for the SAARC region during 1980 to 2018. The panel unit root test summary applied to panel data indicates the first difference order while panel fisher cointegration shows long-run association among the considered variables. The econometric results by fully modified least square (FMOLS) validate the existence of "inverted U-shaped" Kuznets curve for environment as (EKC) and aviation transported carriage (ATC) while "U shaped" aviation transported passenger (ATP) is observed in context to greenhouse gas (GHG). In addition, the dynamic ordinary least square (DOLS) exhibits "inverted U shaped" for aviation transportation while GDP has an increasing trend of "U-shaped" curve. The pairwise Dumitrescu-Hurlin panel causality shows unidirectional association from economic growth, trade openness, and aviation sector to greenhouse gas (GHG) emissions. Therefore, it is an urgent need of the hour for the SAARC region to consider the sustainability of the environment by key sector. This analysis suggests that SAARC nations must focus on exploiting renewable energy means along with implementing fuel-saving traveler and merchandise expertise that thoroughly cuts the diesel fuel.

Adsorption of mesitylene via mesoporous adsorbents

Mesitylene (or 1,3,5-trimethylbenzene) is a volatile organic compound emitted from various industrial processes, e.g., spray coating. Its emissions have become a critical issue because mesitylene is toxic and cannot be removed using traditional adsorbents, e.g., zeolite (H-ZSM-5; the diameter of mesitylene molecules is greater than the pore size of H-ZSM-5). Hence, an adsorbent with a large pore size, MCM-41, is used in this study to investigate its adsorption capacity for mesitylene and compare with that of H-ZSM-5. Experimental results reveal that MCM-41 without Al₂O₃ exhibits a good adsorption capacity (184 mg/g) for the gas stream containing 100 ppm of mesitylene at a relative humidity of 10%. The adsorption kinetics is well described by the Freundlich isotherm. Furthermore, experimental results reveal that MCM-41 is effective for the adsorption of low concentrations (10 ppm) of mesitylene. In addition, adsorption-desorption tests revealed that the sample MCM-41-AS is stable to sustain the adsorption capacity after 10 adsorption-desorption cycles. After 10 adsorption-desorption cycles, MCM-41-AS retains 92.4% of its initial adsorption capacity (170 vs. 184 mg/g). Finally, MCM-41 and H-ZSM-5 in series are effective for the simultaneous removal of mesitylene and toluene in the gas stream.

IMPLICATIONS

This study aims to improve the performance of adsorbent for mesitylene, which is typically applied in the spray-coating industry. The zeolite MCM-41-AS is selected as a candidate for the investigation. Experimental results reveal that MCM-41-AS exhibits a good adsorption capacity for mesitylene and that it can be integrated with H-ZSM-5-25 for the simultaneous adsorption of mesitylene and toluene.

Photocatalytic materials and technologies for air purification

Since there is increasing concern for the impact of air quality on human health, the present work surveys the materials and technologies for air purification using photocatalytic materials. The coverage includes (1) current photocatalytic materials for the decomposition of chemical contaminants and disinfection of pathogens present in air and (2) photocatalytic air purification systems that are used currently and under development. The present work focuses on five main themes. First, the mechanisms of photodegradation and photodisinfection are explained. Second, system designs for photocatalytic air purification are surveyed. Third, the photocatalytic materials used for air purification and their characteristics are considered, including both conventional and more recently developed photocatalysts. Fourth, the methods used to fabricate these materials are discussed. Fifth, the most significant coverage is devoted to materials design strategies aimed at improving the performance of photocatalysts for air purification. The review concludes with a brief consideration of promising future directions for materials research in photocatalysis.

On the underlying mechanisms of the low observed nitrate selectivity in photocatalytic NOxabatement and the importance of the oxygen reduction reaction

Semiconductor photocatalysis could be an effective means to combat air pollution, especially nitrogen oxides, which can be mineralized to nitrate.

A chamber study on the reactions of O3, NO, NO2 and selected VOCs with a photocatalytically active cementitious coating material

Chamber studies were performed to investigate the efficiency of a photocatalytically active cementitious coating material to depollute contaminated air. The results showed a photocatalytic effect on ozone (O3), proven by an increase of the geometric uptake coefficient from 5.2 × 10(-6) for the inactive to 7.7 × 10(-6) for the active material under irradiation. Measured first-order rate constants for nitrogen oxides (NOx) under irradiation are in the range of 2.6-5.9 × 10(-4) s(-1), which is significantly higher compared to the inactive material (7.3-9.7 × 10(-5) s(-1)) demonstrating the photocatalytic effect. However, no significant photocatalytic degradation was observed for the studied volatile organic compounds (VOCs) toluene and isoprene resulting in only an upper limit uptake coefficient of 5.0 × 10(-7) for both VOCs. In all experiments using the photocatalytically active material, a clear formation of small carbonyl (C1-C5) gas phase compounds was identified which is suggested to result from the photocatalytic degradation of organic additives. In contrast to the uptake observed for pure O3, during the experiments with NOx (≥50 % relative humidity), a clear photocatalytic formation of O3 was observed. For the material investigated, an empirically derived overall zero-order rate constant of k 0 (O3) ≈ 5 × 10(7) molecules cm(-3) s(-1) was determined. The results demonstrate the necessity of detailed studies of heterogeneous reactions on such surfaces under more complex simulated atmospheric conditions as enabled by simulation chambers.