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Composites of poly­(vinylidene fluoride-co-hexafluoro propylene) (PVdF-HFP) incorporating 10 wt % bis­(trifluoromethane)­sulfonimide lithium salt (LiTFSI) and 10 wt % particles of nanoparticulate silica (nm-SiO2), nanoparticulate titania (nm-TiO2), and fumed silica (f-SiO2) were prepared by electrospinning. These membranes served as host matrix for the preparation of composite polymer electrolytes (CPEs) following activation with lithium sulfur battery electrolyte comprising 50/50 (vol %) dioxolane/dimethoxyethane with 1 M LiTFSI and 0.1 M LiNO3. The membranes consist of layers of fibers with average fiber diameter of 0.1–0.2 μm. CPEs with f-SiO2 exhibited higher ionic conductivity with a maximum of 1.3 × 10–3 S cm–1 at 25 °C obtained with 10 wt % filler compositions. The optimum CPE based on PVdF-HFP with 10 wt % f-SiO2 exhibited enhanced charge–discharge performance in Li-S cells at room-temperature eliminating polysulfide migration, delivering initial specific capacity of 895 mAh g–1 at 0.1 C-rate and a very low electrolyte/sulfur (E/S) ratios between 3:1 to 4:1 mL.g–1. The CPEs also exhibited very stable cycling behavior well over 100 cycles (fade rate ∼ 0.056%/cycle), demonstrating their suitability for Li-S battery applications. In addition, the interconnected morphological features of PVdF-HFP result in superior mechanical properties (200–350% higher tensile strength). Higher Li-ion conductivity, higher liquid electrolyte uptake (>250%) with dimensional stability, lower interfacial resistance, and higher electrochemical stability are some of the attractive attributes witnessed with these CPEs. With these improved performance characteristics, the PVdF-HFP system is projected herein as suitable polymer electrolytes system for high-performance Li–S rechargeable batteries.

Main TextA megacity typically refers to a metropolitan area with more than 10 million people. The number of megacities worldwide has increased from 8 in 1970 to 34 in 2016 with their total population exceeding 650 million (City Population, 2016). Air pollution, a consequence of increased population and urbanisation, is a common concern in megacities. Here we focus on the Metropolitan Area of São Paulo (MASP), which is the 5 th most populous urban region in the world and the second most populated region in Latin America (UN, 2014), making up ~10% of the total population of Brazil. With 21 million inhabitants and 8511 km 2 area (Fig. 1a), the MASP includes 38 metropolitan areas surrounding the city of São Paulo that has a population of 12 million (IBGE, 2016). What makes São Paulo distinctly different from all other megacities in the world is that its vehicle fleet operates exclusively on biofuel blends (sugarcane ethanol and soya diesel) in diesel, making it a unique biofuel-driven megacity. Yet, São Paulo's air quality face challenges to meet its national standards, which are relatively relaxed compared with the megacities of Asia (e.g., Delhi) or Europe (e.g., London). While the events of highly elevated concentrations of particulate matter (PM) are similarly common as in other megacities, the underlining factors responsible for them are unique to São Paulo and the questions are: (i) how can the air quality be improved considering that numerous interventions have already been taken in controlling emissions from vehicular fleet? (ii) how can the transportation system be transformed to make it emission-neutral? (iii) how the emissions from the main emitters such as the diesel trucks and buses can be reduced? and (iv) how the changes in the content of biofuel in diesel have influenced the exceedances and ozone formation? The aim of this paper is to propose answers to the above questions in the context of distinctness in the vehicle fleet, hitherto overlooked sources, underlining causes for pollution exceedances, and to suggest future directions and research needs to better understand and manage air quality of this unique megacity.Unique vehicle fleet and fuels it operates on: The MASP includes more than 7 million of road vehicles, with an average of 0.34 vehicles per inhabitant (CETESB, 2015). Light duty vehicles (LDVs), including private cars and taxis, dominate the traffic fleet with 85% share, followed by motorcycles (12%) and heavy duty vehicles (HDVs; 3%) (CETESB, 2013). The fleet of LDV, HDV and motorcycle have increased by 12.7, 10 and 9.6% between 2009 and 2012, respectively. The proportion of flexfuel vehicles that can run on ethanol or gasohol (gasoline with 25-27% ethanol) is increasing in MASP every day as 94% of vehicles sold in 2013 were flex-fuel (Posada and Façanha, 2015). Currently, the proportion of gasohol-driven LDVs is 55%, followed by flex-fuel vehicles (38%), ethanol (4%) and diesel (2%) (CETESB, 2012). To enable comparison, the relevant characteristics of the five world's largest megacitie...

Mobility restrictions are among actions to prevent the spread of the COVID-19 pandemic and have been pointed as reasons for improving air quality, especially in large cities. However, it is crucial to assess the impact of atmospheric conditions on air quality and air pollutant dispersion in the face of the potential variability of all sources. In this study, the impact of mobility restrictions on the air quality was analyzed for the most populous Brazilian State, São Paulo, severely impacted by COVID-19. Ground-based air quality data (PM 10 , PM 2.5 , CO, SO 2 , NO x , NO 2 , NO, and O 3 ) were used from 50 automatic air quality monitoring stations to evaluate the changes in concentrations before (January 01 - March 25) and during the partial quarantine (March 16 - June 30). Rainfall, fires, and daily cell phone mobility data were also used as supplementary information to the analyses. The Mann-Whitney U test was used to assess the heterogeneity of the air quality data during and before mobility restrictions. In general, the results demonstrated no substantial improvements in air quality for most of the pollutants when comparing before and during restrictions periods. Besides, when the analyzed period of 2020 is compared with the year 2019, there is no significant air quality improvement in the São Paulo State. However, special attention should be given to the Metropolitan Area of São Paulo (MASP), due to the vast population residing in this area and exposed to air pollution. The region reached an average decrease of 29% in CO, 28% in NO x , 40% in NO, 19% in SO 2 , 15% in PM 2.5 , and 8% in PM 10 concentrations during the mobility restrictions period compared to the same period in 2019. The only pollutant that showed an increase in concentration was ozone, with a 20% increase compared to 2019 during the mobility restrictions period. Before the mobility restrictions period, the region reached an average decrease of 30% in CO, 39% in NO x , 63% in NO, 12% in SO 2 , 23% in PM 2.5 , 18% in PM 10 , and 16% in O 3 concentrations when compared to the same period in 2019. On the other hand, Cubatão, a highly industrialized area, showed statistically significant increases above 20% for most monitored pollutants in both periods of 2020 compared to 2019. This study reinforces that the main driving force of pollutant concentration variability is the dynamics of the atmosphere at its various time scales. An abnormal rainy season, with above average rainfall before the restrictions and below average after it, generated a scenario in which the probable significant reductions in emissions did not substantially affect the concentration of pollutants.