Low Pollutant Emissions Research Articles

Pressure dependence of combustion instability for premixed syngas/air in a closed channel

Syngas is a promising alternative energy carrier with low carbon and pollutants emissions, which has huge application potential in internal combustion engines and gas turbines. The combustion characteristics of stoichiometric syngas/air mixtures with varied initial pressure (0.5–2.5 atm) and hydrogen content (10%–90% v/v) were examined through experiments in a rectangular closed channel. The flame images and overpressure dynamics were captured by high-speed schlieren photography and pressure sensors. The flame instabilities and the flame-acoustic wave interaction were explored. The results showed that the flame morphology and dynamics were enhanced with increasing hydrogen content and initial pressure. The Darrius-Landau instability has an impact on flame deformation, which was strengthened with growing initial pressure, while the thermo-diffusive instability could be neglected during combustion. At later stages after tulip inversion, the flame-acoustic wave interaction was relatively outstanding inducing wrinkled flame front and cellular structures on the flame surface.

Influence of Glycerol on Methanol Fuel Characteristics and Engine Combustion Performance

Methanol derived from solar energy is a carbon-neutral alternative fuel for engines. The low viscosity of methanol is one of the problems that restrict its direct compression ignition application in engines. Glycerol is a renewable resource derived from biomass, and its viscosity is more than 1700 times that of methanol. In this study, glycerol was mixed with methanol in different volume fractions (1–50%), and a methanol-glycerol mixture with similar viscosity to diesel was prepared. Then, the particle size, electrical conductivity, viscosity, swelling and corrosion characteristics of the mixed fuel were measured. Finally, the combustion and emission tests of methanol-glycerol mixed fuel were carried out on a heavy-duty multi-cylinder diesel engine. The results show that glycerol can effectively adjust the viscosity of the mixed fuel. The viscosity of the mixed fuel can reach 3.19 mm2/s at 20 °C when blended with 30% glycerol by volume, which meets the requirements of the national standard for diesel fuel. The addition of glycerol can alleviate the corrosion of methanol to the polymer. The test of the mixed fuel in the direct compression ignition engine shows that the thermal efficiency of methanol mixed with 5% glycerol was further improved than that of pure methanol, both of which were significantly higher than the thermal efficiency of diesel compression ignition engines. Methanol and 5% glycerol by volume blends can reduce soot and nitrogen oxide emissions while maintaining low HC and CO emissions. Therefore, proper blending of glycerol in methanol fuel can optimize the fuel properties of methanol and achieve higher thermal efficiency and lower pollutant emissions than pure methanol direct compression ignition.

Does China's Eco-Province Policy Effectively Reduce the Pollutant Emission Intensities?

Economic development and environmental conservation are two important challenges for China. A series of initiatives including Eco-province (EP) policies have been taken to achieve sustainable development by the Chinese government. Increasing concerns regarding policy implications on sustainable development have increased attention to the topic. However, the research on the relationship between economic development and pollutant (COD, SO2) emission intensities after the implementation of EP policy remains inadequate. We applied a Time-Varying Difference-in-Differences Model by employing Chinese provincial panel data to quantitatively study the policy effect, and further utilized the Mediating Effect Model to analyze the mechanism. The article generates several findings: (1) The EP policy had overall inhibitory effects on both COD and SO2 emission intensities, and it would reduce the emission intensity by 4.99% and 6.77% on average, respectively. However, there was a five year lag in the policy effect. (2) The policy effect was significant in the western and central provinces with high pollutant emission intensities, but not in the eastern provinces. (3) The primary inhibiting mediating effects of Eco-province policy to lower pollutant emission intensity were increased GDP per capita and inventions.

LbSP: Load-Balanced Secure and Private Autonomous Electric Vehicle Charging Framework With Online Price Optimization

Nowadays, autonomous electric vehicles (AEVs) are increasingly popular due to low resource consumption, low pollutant emission, and high efficiency. In practice, Vehicle-to-Grid (V2G) networks supply energy power to EVs to ensure the usage of EVs. However, there are still certain security and privacy concerns in V2G connections, such as identity impersonation and message manipulation. Additionally, the widespread usage of EVs brings significant pressure on the power grid, leading to undesirable effects like voltage deviations if EVs’ charging is not well coordinated. In this article, to tackle these issues, we design a novel load-balanced secure and private EV charging framework named load-balanced secure and private framework (LbSP) for secure, private, and efficient EV charging with a minimal negative effect on the existing power grid. It assures reliable and efficient charging services by a lightweighted encryption technique. Also, it balances the energy consumption of power grids via an online pricing strategy that minimizes load variance by optimizing energy prices in real time. Moreover, it preserves users’ privacy while not affecting online pricing using an advanced differential privacy technique. Furthermore, LbSP deploys on an edge-cloud structure for fast response and more precise pricing, where clouds balance overall load consumption by online price optimization while edges gather data for clouds and respond to charging requests from EVs. The evaluation results show that the proposed framework ensures secure and private EV charging, balances energy load consumption, and preserves users’ privacy.

Decarbonization of a tissue paper plant: Advanced numerical simulations to assess the replacement of fossil fuels with a biomass-derived syngas

Numerical simulations based on Computational Fluid Dynamic techniques are performed to analyze the possibility of feeding a biomass-derived syngas into the combustion chamber upstream of the hoods for tissue-paper drying, to replace fossil fuels and thus decarbonize the plant. It was observed that, in the context of Favre-Averaged Navier–Stokes equations simulation, syngas requires detailed kinetics and finite-rate approaches, as the fast-chemistry ones, largely employed in the industrial practice for conventional fuels, lead to unreliable results. The actual chamber, originally designed to be fed with liquid petroleum gas, does not operate properly when fueled with syngas, with incomplete oxidation of carbon monoxide. Numerical simulations have proven how very few modifications of the chamber can be devised to permit feeding efficiently the syngas, obtaining low pollutant emissions and meeting the desired requirements in terms of flow and thermal uniformity for the drying process. The solution proposed in the present study, with the effective use of a biomass-derived syngas to feed the drying section of a tissue paper plant, will allow saving approximately 8500 ton/y of CO2 emissions in comparison with today’s fossil fuel carbon footprint.

A density functional theory study of catalytic oxygen reduction reaction on Co-CoO(111)

The demand for clean energy has greatly increased given the current situation of environmental pollution and energy shortages. Fuel cells have attracted much attention because of their high energy density and low pollutant emission. However, the oxygen-reduction reaction (ORR) kinetics of the cathode are slow, and many platinum-based catalysts are needed to drive the reaction. The high platinum price and scarce reserves limit the application of fuel cells. It is therefore urgent to develop cheaper and more efficient non-noble-metal catalysts to drive the ORR. One promising approach is to develop transition-metal-oxide catalysts with high ORR catalytic performance. Here, the structure of CoO was modified, and the surface of partially reduced CoO(111) catalyst [Co-CoO(111)] was simulated via density functional theory (DFT). The catalytic ORR on two kinds of Co (Co-2, Co-3) on the Co-CoO(111) surface were simulated and free-energy diagrams were created. When Co-2 was used as the active site, the Co-CoO(111) catalyst had a low overpotential of 0.34 eV. Besides, when Co-3 site was covered with O and Co-2(*)-Co-3(O*) is used as ORR reaction site, it still had good catalytic performance of ORR. The electronic structure of Co-CoO(111) was used to explain the high level of the ORR.

Simultaneous reduction of nitrogen oxides and sulfur dioxide in circulating fluidized bed combustor during oxy-coal combustion

For stable carbon capture utilization and storage, highly-pure CO2 content and low pollutant emissions must be maintained throughout oxy-coal firing operation; however, studies on combining absorbent addition and oxidant staging combustion to eliminate simultaneous nitrogen oxides (NO, N2O) and sulfur dioxide (SO2) have not been reported. Accordingly, the purpose of this study was to investigate the effects of oxidant staging and limestone addition on the reductions of NO, N2O, and SO2 emissions in an oxy-circulating fluidized bed combustor at 25% and 31% input oxygen. The operating parameters considered in this study were: oxidant compositions; corresponding flow rate ratios; primary, secondary, and tertiary oxidants (PO, SO, and TO, respectively); TO supply heights; and limestone addition. The results revealed that compared to the TO supply heights, increasing TO flow rate was more effective at reducing the nitrogen oxide emissions. Under an optimal flow rate ratio (PO:SO:TO = 70:10:20) and TO height (6.4 m), NO, N2O, and SO2 emissions were ≈7.4, 4.2 and 4.1 mg MJ−1, respectively. The increase in SO2 emission caused by the application of oxidant staging could be effectively decreased by 60.6% without impacting combustion performance via limestone injection into the combustor; effectively facilitating the production of >86 vol% CO2. These findings can serve as valuable references for future designs, and the efficient operation of oxy-coal combustion plants constructed at larger scales, thereby ensuring highly-pure CO2 content and low pollutant emissions.

Reduced Pollutant Emissions and Slagging Rate of Biomass Pellet Combustion by Optimizing the Multilayer Distribution of Secondary Air.

The utilization of coal and other fossil fuels is becoming increasingly restricted. Biomass, as a clean and renewable energy, plays a significant role in achieving zero carbon emissions. However, biomass is prone to slagging in the combustion process due to its high alkali metal content. The ash slagging rate and pollutant emission level of flue gas can be reduced by optimizing the air distribution, in order to decrease the fuel layer temperature in the combustion chamber. The results reveal opposite change trends of CO and NOx concentrations in the flue gas. The NOx emissions of corn stalk combustion under the multilayer secondary air distribution are obvious compared with those of rice husk combustion. The slagging rate of corn stalks is highly correlated with temperature T1 of the fuel bed. The silica ratio (G), alkali/acid ratio (B/A), Na content index (Na (index)), and alkaline index (Alc) cannot accurately predict the slagging tendency when temperature T1 changes. Therefore, the modified predictive index (Gt) was proposed to predict the slagging tendency of corn stalks with the combustion zone temperature T1 effectively. The experimental results can contribute to the efficient combustion and low pollutant emissions of biomass.

Thermally stable nanoclay and functionalized graphene oxide integrated SPEEK nanocomposite membranes for direct methanol fuel cell application

Membrane-based fuel cells, particularly methanol-based fuel cells, are thriving areas with high efficiency, less material consumption, and low emission of pollutants. But commercial membranes have less thermal withstanding ability and high cost, so alternative polymeric membranes have been developed with desired properties to overcome this issue. The SPEEK membrane was fabricated with halloysite nanoclay and functionalized graphene oxide (f-GO) nanocomposites at various concentrations via dry phase inversion. The sulfonic acid group in the SPEEK and silane functionalization of GO enhanced the Ion exchange capacity from 0.22 to 0.35 meq/g which enhances the proton conductivity. Furthermore, the thermal stability and hydrophilicity of the pristine SPEEK membrane were reformed with addition of halloysite nanoclay and f-GO in SPEEK membrane. The presence of nanocomposite on the surface of the SPEEK membranes was confirmed via scanning electron microscope (SEM) analysis. The 3 wt% halloysite nanoclay and 2 wt% of f-GO composite membrane was hold the 0.47 mS cm−1 of proton conductivity and 72.2 mW cm−2 of power density, whereas pristine SPEEK membrane was 0.31 mS cm−1 and 28 mW cm−2, respectively. The 3 wt% halloysite incorporated SPEEK membrane and 1.5 wt% f-GO incorporated SPEEK membrane was shown better proton conductivity, which act as a prominent membrane for direct methanol fuel cell (DMFC) applications.

Effects of direct injection and mixture enleament on the combustion of hydrous ethanol and an ethanol-gasoline blend in an optical engine

Ethanol is a renewable fuel and can be used in electric hybrid vehicles concepts, especially for countries capable of producing such fuel in a sustainable way. A strategy to enhance these concepts is the use of lean-burn combustion, which is an effective way to improve the fuel economy from spark-ignition engines, while obtaining low pollutant emissions. However, these improvements are complicated to achieve in a practical way because lean combustion has low rates of reaction, extinction, and misfire cycles, leading to cyclical variability for the engine operation. The drawback becomes even greater when lean combustion is associated with commercial ethanol fuels and direct injection. Therefore, the objective of the present work is to provide an experimental analysis of spray guided direct injection with commercial fuels used in a consolidated market for the use of ethanol such as the Brazilian one, in particular hydrous ethanol (E95W05) and ethanol-gasoline blends (E27G73). The experiments were conducted in an optically accessible spark-ignition engine and the lean combustion effects on engine cycle variability, performance, flame morphology, and exhaust emissions were assessed. In general, the results indicated that combustion instabilities can be correlated from thermodynamic and optical analyses. Flame instabilities for E95W05 were associated with the lower flame propagation speed caused by the temperature reduction during lean combustion. Additionally, exhaust emissions contained the presence of unburned ethanol which increased when combustion became leaner. Moreover, the lower flame propagation speed was one of the factors responsible for reducing engine performance and increasing combustion variability. The results indicated that vaporization was a relevant phenomenon affecting ethanol combustion in the direct injection mode. The cooling effect of fuel vaporization presented itself as a powerful means for the reduction of NOx and aldehydes, even for the lean operation. Higher emissions of CO and THC were also observed for the engine operating with E95W05 when compared to E27G73. The results of the present work showed that special attention must be paid to the use of commercial fuel with a high ethanol content in spray-guided direct injection engines, especially during lean-burn combustion, in order to not compromise the performance nor increase pollutant emissions.

Investigation of the Effects of Fuel Cells on V-Q & V-P Characteristics

In this paper, the use of a FC system connected to the network is proposed as a source of DG with high reliability, and for this purpose, the dynamic model of the fuel cell has been simulated. A hybrid system of fuel cell distributed generation (FCDG) is presented to provide electrical energy for a small isolated area. Boost converter (DC/DC), in order to increase the voltage level of the system and stabilize the DC link voltage has been used, which provides the possibility of connecting several different scattered production sources in parallel. Voltage stability is concerned with the ability of a power system to maintain acceptable bus voltages under normal conditions and after being subjected to a disturbance. The use of DG sources has many advantages, including meeting peak load needs, reducing network losses, providing reactive power locally, and regulating network voltage. Among all sources of distributed production, fuel cells are of special importance due to their high efficiency, high energy density, the ability to simultaneously produce heat and electric power, and low emission of pollutants. Using fuel cells (FCs) have several advantages and in this paper we investigate the effects of FCs on power systems via simulation a single machine (DG as small gas turbine coupled with a FC) in the Dig Silent area for different PF of FC. Different PF for FC obtained with control the DC to AC inverter. We found that by control the PF of FCs, we can increase the limitation of reactive generation of overall system and improve the V-P V-Q characteristics of overall system. With the grid-connected inverter's switching control, the active and reactive power injected into the grid is controlled independently.

Influence of fuel injection pressure and RME on combustion, NOx emissions and soot nanoparticles characteristics in common-rail HSDI diesel engine

‏ Manipulating in fuel injection strategies and introduce renewable fuel in diesel engine can provide clean combustion and lower pollutant emissions. The effect of fuel injection pressures (FIPs) and RME on combustion characteristics, NOx emissions and soot nanoparticle emissions when rapeseed methyl esters was used have been investigated at 1500 rpm and two brake mean effective pressure of 2.5 and 5 bar. A calibrated electrostatic mobility spectrometer (EMS) was used to measure the soot nanoparticle number size distributions. The peak cylinder pressure and heat release rates were evaluated when the FIP increased for all fuels studied. The results showed that further advanced in combustion with RME, meanwhile a shorter ignition delay from the fuel was exhibited in comparison with diesel fuel combustion under various FIP. Furthermore, the values of BSFC decreased by 3.7% and 17.8% from the RME combustion at high and low engine load, respectively. The reduction in NOx emissions was obtained when FIP increased during RME combustion in comparison with ULSD under low engine load. In contrast, RME generated higher NOx by 7% and lower soot nanoparticles by 27% compared to the ULSD under high engine load. RME combustion produced lower nucleation particle numbers in comparison with those emitted from ULSD under all engine operating conditions as well as the accumulation mode particles was higher for ULSD.

Exploring the potentials of lean-burn hydrogen SI engine compared to methane operation

The global rush for decarbonization and the more restrictive emission regulations are pushing the research for cleaner powertrains to the transport sector. In this sense, this work contributes with an experimental investigation of the performance and emissions of a single-cylinder SI engine operating under lean-burn hydrogen combustion. Its performance, combustion parameters, exhaust emissions, and indicated efficiency for a wide range of mixture dilutions are then compared to methane under similar engine load conditions. Hydrogen achieved stable combustion up to lambda 3.4, presenting zero CO emission and very low HC emission for all tested operating conditions. Hydrogen operation also presented zero NOx emissions for conditions leaner than lambda 2.2 and 3.0 at 2000 and 3000 rpm, respectively, however, the NOx emissions increase as the mixture is enriched. The high in-cylinder pressure rise rate limited the operation at mixtures richer than lambda 1.3 at 2000 rpm. When compared to methane, the hydrogen allows de-throttle the engine to burn lean mixtures maintaining a proper flame speed, resulting in lower pumping losses, lower pollutants emissions for most of the conditions tested, and higher indicated efficiency, making hydrogen a promising fuel to replace conventional fuels on cleaner SI engines.

Exploration of Joint Optimization and Visualization of Inventory Transportation in Agricultural Logistics Based on Ant Colony Algorithm.

The problem of joint optimization of inventory and transportation in agricultural logistics and distribution is a typical logistics problem, but agricultural logistics and distribution also have their own characteristics, such as uneven distribution of outlets, complex road conditions, very many outlets, a single order with few goods but high frequency of ordering, centralized distribution, and unified channels. To promote the sustainable development of the economy, it is necessary to save energy and reduce emissions, and eventually enter a new era of “low consumption, low pollution, and low emissions.” Modern logistics vehicle-scheduling process is complex and changeable, and the existing mathematical methods are not perfect in solving this problem, lacking scientific theory as a guide. The joint optimization problem introduces the inventory change factor on the basis of periodic vehicle path optimization and optimizes the inventory decision and path planning in an integrated manner. As a system to support the logistics industry, the visualized logistics information system is capable of video viewing and querying logistics information. In order to reduce gas emissions and save costs, it is necessary to optimize the transportation link, and the focus of optimization is the route optimization of distribution vehicles. Ant colony algorithm (ACA) is an emerging search and optimization technique, which emerged from the research of ACA. In this study, we study the joint optimization and visualization of inventory transportation in agricultural logistics based on ACA. In addition, the experimental results show that the inventory cost/total cost of improved ACA is 0.006 when the unit mileage transportation cost is 10, and the IBM ILOG CPLEX is 0.031, which is reduced by 0.0025, that is to say, in the case of high inventory cost per unit product, the use of improved ACA can lead to a significant reduction in inventory costs. Therefore, it can realize the whole process of control, traceability, and dynamic optimization to ensure the timeliness of emergency finished food security and provide real-time information for decision-making in command as well.

Research on energy-saving packaging design based on artificial intelligence

Background:Low-carbon economy is an economic model based on low energy consumption, low pollution and low emission. Energy-saving packaging design is an idea that guides the practice reform and development under the guidance of consumers’ green psychology. It takes the green design concept of modern eco-environmental protection and other development concepts as the main standard of packaging design application practice. Objective:In order to change this situation, we should combine people’s formed green psychology, so as to find a way of green packaging design. Methods:This paper discusses the application and development of energy-saving packaging design. Based on artificial intelligence (AI) technology, it realizes the combination of market and green environmental protection design, and improves product utilization and production efficiency. For judging the type of intelligent energy-saving packaging, the confidence weight database decision algorithm is adopted, and the basic principle is to assume that AI neural network forms the energy consumption vector. Conclusion:For the long-term benefit of human survival, packaging designers should re-examine the relationship between design and natural environment, reduce the pollution components in packaging design, take environmental protection as the top priority of design, and establish a design concept that conforms to ecological ethics. Intelligent packaging technology realizes the integration and management of product packaging information, which is conducive to people’s better understanding of products and is of great significance to the development of low-carbon product packaging.

Recent developments in high-performance Nafion membranes for hydrogen fuel cells applications

As a promising alternative to petroleum fossil energy, polymer electrolyte membrane fuel cell has drawn considerable attention due to its low pollution emission, high energy density, portability, and long operation times. Proton exchange membrane (PEM) like Nafion plays an essential role as the core of fuel cell. A good PEM must have satisfactory performance such as high proton conductivity, excellent mechanical strength, electrochemical stability, and suitable for making membrane electrode assemblies (MEA). However, performance degradation and high permeability remain the main shortcomings of Nafion. Therefore, the development of a new PEM with better performance in some special conditions is greatly desired. In this review, we aim to summarize the latest achievements in improving the Nafion performance that works well under elevated temperature or methanol-fueled systems. The methods described in this article can be divided into some categories, utilizing hydrophilic inorganic material, metal-organic frameworks, nanocomposites, and ionic liquids. In addition, the mechanism of proton conduction in Nafion membranes is discussed. These composite membranes exhibit some desirable characteristics, but the development is still at an early stage. In the future, revolutionary approaches are needed to accelerate the application of fuel cells and promote the renewal of energy structure.

Enabling mMTC in Remote Areas: LoRaWAN and LEO Satellite Integration for Offshore Wind Farm Monitoring

The offshore wind farms are gaining momentum due to their promise to offer sustainable energy with low pollution and greenhouse gas emission. However, despite all the immense technological progress of recent years, the operation in a harsh and hard-to-reach environment remains challenging. According to the reports, each offshore wind turbine requires five maintenance visits a year on average, and the cumulative repair costs constitute around 30% of the turbine’s life-cycle expenditure. Motivated by the advancement of massive machine-type connectivity (mMTC) and satellite technologies, in this study, we investigate the potential of these to enable remote monitoring of the offshore wind farms. Specifically, the two alternative architectures are considered. The indirect architecture relies on using a local mMTC gateway (GW) with a backbone over a reliable communication channel (e.g., satellite or wire-based). The direct approach implies the transmission of the data by sensors on the wind turbines directly to the mMTC GW on the low-Earth-orbit satellite. The details of the system design, the alternative implementation strategies, and relevant pros, cons, and tradeoffs are pin-pointed. Finally, we employ simulations using realistic deployment and traffic and advanced propagation and collision models to characterize these two approaches’ feasibility and packet delivery probability numerically when implemented over LoRaWAN mMTC technology.

The Impact of the Numbers of Monitoring Stations on the National and Regional Air Quality Assessment in China During 2013-18.

China national air quality monitoring network has become the core data source for air quality assessment and management in China. However, during network construction, the significant change in numbers of monitoring sites with time is easily ignored, which brings uncertainty to air quality assessments. This study aims to analyze the impact of change in numbers of stations on national and regional air quality assessments in China during 2013–18. The results indicate that the change in numbers of stations has different impacts on fine particulate matter (PM2.5) and ozone concentration assessments. The increasing number of sites makes the estimated national and regional PM2.5 concentration slightly lower by 0.6–2.2 µg m−3 and 1.4–6.0 µg m−3 respectively from 2013 to 2018. The main reason is that over time, the monitoring network expands from the urban centers to the suburban areas with low population densities and pollutant emissions. For ozone, the increasing number of stations affects the long-term trends of the estimated concentration, especially the national trends, which changed from a slight upward trend to a downward trend in 2014–15. Besides, the impact of the increasing number of sites on ozone assessment exhibits a seasonal difference at the 0.05 significance level in that the added sites make the estimated concentration higher in winter and lower in summer. These results suggest that the change in numbers of monitoring sites is an important uncertainty factor in national and regional air quality assessments, that needs to be considered in long-term concentration assessment, trend analysis, and trend driving force analysis.

Haze Occurrence Caused by High Gas-to-Particle Conversion in Moisture Air under Low Pollutant Emission in a Megacity of China.

Haze occurred in Zhengzhou, a megacity in the northern China, with the PM2.5 as high as 254 μg m−3 on 25 December 2019, despite the emergency response measure of restriction on the emission of anthropogenic pollutants which was implemented on December 19 for suppressing local air pollution. Air pollutant concentrations, chemical compositions, and the origins of particulate matter with aerodynamic diameter smaller than 2.5 µm (PM2.5) between 5–26 December were investigated to explore the reasons for the haze occurrence. Results show that the haze was caused by efficient SO2-to-suflate and NOx-to-nitrate conversions under high relative humidity (RH) condition. In comparison with the period before the restriction (5–18 December) when the PM2.5 was low, the concentration of PM2.5 during the haze (19–26 December) was 173 µg m−3 on average with 51% contributed by sulfate (31 µg m−3) and nitrate (57 µg m−3). The conversions of SO2-to-sulfate and NOx-to-nitrate efficiently produced sulfate and nitrate although the concentration of the two precursor gases SO2 and NOx was low. The high RH, which was more than 70% and the consequence of artificial water-vapor spreading in the urban air for reducing air pollutants, was the key factor causing the conversion rates to be enlarged in the constriction period. In addition, the last 48 h movement of the air parcels on 19–26 December was stagnant, and the air mass was from surrounding areas within 200 km, indicating weather conditions favoring the accumulation of locally-originated pollutants. Although emergency response measures were implemented, high gas-to-particle conversions in stagnant and moisture circumstances can still cause severe haze in urban air. Since the artificial water-vapor spreading in the urban air was one of the reasons for the high RH, it is likely that the spreading had unexpected side effects in some certain circumstances and needs to be taken into consideration in future studies.

Passive Small Direct Alcohol Fuel Cells for Low-Power Portable Applications: Assessment Based on Innovative Increments since 2018

Passive small direct alcohol fuel cells (PS-DAFCs) are compact, standalone devices capable of electrochemically converting the chemical energy in the fuel/alcohol into electricity, with low pollutant emissions and high energy density. Thus, PS-DAFCs are extremely attractive as sustainable/green off-grid low-power sources (milliwatts to watts), considered as alternatives to batteries for small/portable electric and electronic devices. PS-DAFCs benefit from long life operation and low cost, assuring an efficient and stable supply of inherent non-polluting electricity. This review aims to assess innovations on PS-DAFC technology, as well as discuss the challenges and R&D needs covered on practical examples reported in the scientific literature, since 2018. Hence, this compilation intends to be a guidance tool to researchers, in order to help PS-DAFCs overcome the barriers to a broad market introduction and consequently become prime renewable energy converters and autonomous micropower generators. Only by translating research discoveries into the scale-up and commercialization process of the technology can the best balance between the economic and technical issues such as efficiency, reliability, and durability be achieved. In turn, this will certainly play a crucial role in determining how PS-DAFCs can meet pressing sustainable energy needs.