•Yolk-shelled ZnCo2O4 structures have been synthesized by a one-step co-precipitation method.•FESEM images revealed that the morphology is based on a yolk-shelled shape.•The yolk-shelled ZnCo2O4 ...exhibits a good sensitivity towards sub-ppb (80-890 ppb) level of ozone.•The sensor worked within a wide range of ozone concentrations,being also selective to ozone compared to CO, NH3 and NO2.
The need to improve the sensitivity, selectivity and stability of ozone gas sensors capable of monitoring the environment to prevent hazard to humans has sparked research on binary metal oxides. Here we report on a novel ozone gas sensor made with ca. 0.5μm yolk-shelled ZnCo2O4 microstructures synthesized via an eco-friendly, co-precipitation method and subsequent annealing. With these ZnCo2O4 microspheres, ozone concentrations down to 80 parts per billion (ppb) could be detected with a.c. and d.c. electrical measurements. The sensor worked within a wide range of ozone concentrations, from 80 to 890ppb, being also selective to ozone compared to CO, NH3 and NO2. The high performance could be attributed to the large surface area to volume ratio inherent in yolk-shell structures. Indeed, ozone molecules adsorbed on the ZnCo2O4 surface create a layer of holes that affect the conductivity, as in a p-type semiconductor. Since this mechanism of detection is generic, ZnCo2O4 microspheres can be further used in other environment monitoring devices.
•We tested a high number of commercial sensors on the same site, applying the same data treatment and evaluation.•We tested sensors’ response modelling with and without interfering compounds or ...temperature and humidity corrections.•Data Quality Objectives of the Air quality Directive should be met for CO using a cluster of sensors.•Long term real field measurements.
In this work the performances of several field calibration methods for low-cost sensors, including linear/multi linear regression and supervised learning techniques, are compared. A cluster of either metal oxide or electrochemical sensors for nitrogen monoxide and carbon monoxide together with miniaturized infra-red carbon dioxide sensors was operated. Calibration was carried out during the two first weeks of evaluation against reference measurements. The accuracy of each regression method was evaluated on a five months field experiment at a semi-rural site using different indicators and techniques: orthogonal regression, target diagram, measurement uncertainty and drifts over time of sensor predictions. In addition to the analyses for ozone and nitrogen oxide already published in Part A 1, this work assessed if carbon monoxide sensors can reach the Data Quality Objective (DQOs) of 25% of uncertainty set in the European Air Quality Directive for indicative methods. As for ozone and nitrogen oxide, it was found for NO, CO and CO2 that the best agreement between sensors and reference measurements was observed for supervised learning techniques compared to linear and multilinear regression.
Purpose
Life cycle impact assessment (LCIA) translates emissions and resource extractions into a limited number of environmental impact scores by means of so-called characterisation factors. There ...are two mainstream ways to derive characterisation factors, i.e. at midpoint level and at endpoint level. To further progress LCIA method development, we updated the ReCiPe2008 method to its version of 2016. This paper provides an overview of the key elements of the ReCiPe2016 method.
Methods
We implemented human health, ecosystem quality and resource scarcity as three areas of protection. Endpoint characterisation factors, directly related to the areas of protection, were derived from midpoint characterisation factors with a constant mid-to-endpoint factor per impact category. We included 17 midpoint impact categories.
Results and discussion
The update of ReCiPe provides characterisation factors that are representative for the global scale instead of the European scale, while maintaining the possibility for a number of impact categories to implement characterisation factors at a country and continental scale. We also expanded the number of environmental interventions and added impacts of water use on human health, impacts of water use and climate change on freshwater ecosystems and impacts of water use and tropospheric ozone formation on terrestrial ecosystems as novel damage pathways. Although significant effort has been put into the update of ReCiPe, there is still major improvement potential in the way impact pathways are modelled. Further improvements relate to a regionalisation of more impact categories, moving from local to global species extinction and adding more impact pathways.
Conclusions
Life cycle impact assessment is a fast evolving field of research. ReCiPe2016 provides a state-of-the-art method to convert life cycle inventories to a limited number of life cycle impact scores on midpoint and endpoint level.
Chlorine photolysis is an advanced oxidation process which relies on photolytic cleavage of free available chlorine (i.e., hypochlorous acid and hypochlorite) to generate hydroxyl radical, along with ...ozone and a suite of halogen radicals. Little is known about the impact of wavelength on reactive oxidant generation even though chlorine absorbs light within the solar spectrum. This study investigates the formation of reactive oxidants during chlorine photolysis as a function of pH (6–10) and irradiation wavelength (254, 311, and 365 nm) using a combination of reactive oxidant quantification with validated probe compounds and kinetic modeling. Observed chlorine loss rate constants increase with pH during irradiation at high wavelengths due to the higher molar absorptivity of hypochlorite (pK a = 7.5), while there is no change at 254 nm. Hydroxyl radical and chlorine radical steady-state concentrations are greatest under acidic conditions for all tested wavelengths and are highest using 254 and 311 nm irradiation. Ozone generation is observed under all conditions, with maximum cumulative concentrations at pH 8 for 311 and 365 nm. A comprehensive kinetic model generally predicts the trends in chlorine loss and oxidant concentrations, but a comparison of previously published kinetic models reveals the challenges of modeling this complex system.
•Photocatalytic ozonation is a powerful oxidation process for water/wastewater treatment.•Synergistic effects are observed by combining various photocatalysts with ozone.•Photocatalytic ozonation is ...often more cost-effective than ozonation and photocatalysis.•Photocatalytic ozonation can moderate the poor mass transfer of fixed catalysts.•Changing the operational conditions can significantly affect the oxidation efficiency.
The present study aims to describe photocatalytic ozonation as a combination of two different techniques for hydroxyl radical generation; photocatalysis and ozonation, and to highlight its advantages for water and wastewater treatment compared to these two technologies. An extensive review on the mechanisms, kinetics and economic aspects of photocatalytic ozonation has been performed to explore the synergistic effects produced by applying this oxidation method to the degradation, mineralisation and detoxification of different organic pollutants in aqueous media. The influence of experimental parameters such as pollutant concentrations, ozone dose, photocatalytic load and properties, solution pH and temperature, irradiation wavelength and intensity and the effect of the presence of some substances on the efficiency of photocatalytic ozonation is discussed. Finally, plasma-induced photocatalytic systems are introduced as a new approach for handling photocatalytic ozonation treatments.
•Degradation of carbamazepine using combined processes based on hydrodynamic cavitation.•Understanding into effect of operating pressure and pH of wastewater.•Comparison of different treatment ...approaches at large scale operation in terms of cavitational yield and economics.•Combined process gives higher extent of degradation resulting into synergistic effects.•Optimized approach involving hydrodynamic cavitation, ozone and hydrogen peroxide is the best.
Degradation of carbamazepine (CBZ), a widely detected recalcitrant pharmaceutical in sewage treatment plant (STP) effluent, has been studied in the present work using combination of hydrodynamic cavitation (HC) and advanced oxidation processes (AOPs). Due to its recalcitrant nature, it cannot be removed effectively by the conventional wastewater treatment plants (WWTPs) which make CBZ a pharmaceutical of very high environmental relevance and impact as well as stressing the need for developing new treatment schemes. In the present study, the effect of inlet pressure (3–5bar) and operating pH (3–11) on the extent of degradation have been initially studied with an objective of maximizing the degradation using HC alone. The established optimum conditions as pressure of 4bar and pH of 4 resulted in maximum degradation of CBZ as 38.7%. The combined approaches of HC with ultraviolet irradiation (HC+UV), hydrogen peroxide (HC+H2O2), ozone (HC+O3) as well as combination of HC, H2O2 and O3 (HC+H2O2+O3) have been investigated under optimized pressure and operating pH. It was observed that a significant increase in the extent of degradation is obtained for the combined operations of HC+H2O2+O3, HC+O3, HC+H2O2, and HC+UV with the actual extent of degradation being 100%, 91.4%, 58.3% and 52.9% respectively. Kinetic analysis revealed that degradation of CBZ fitted into first order kinetics model for all the approaches. The processes were also compared on the basis of cavitational yield and also in terms of total treatment cost. Overall, it has been demonstrated that combined process of HC, H2O2 and O3 can be effectively used for treatment of wastewater containing CBZ.
To comprehensively understand meteorological drivers for the soaring ozone pollution across China, an advanced causality analysis model, Convergent Cross Mapping (CCM) was employed to investigate the ...causal influence of major individual meteorological factors on ground ozone concentrations in 184 monitoring cities. Meteorological influences on O3_1h and O3_8h were generally consistent. For most mega cities, temperature, humidity and sunshine duration (SSD) exerted a major influence on ground ozone concentrations in all seasons. Specifically, temperature was the most important meteorological factor for ground ozone concentrations across China. From the perspective of influence direction, temperature, SSD and evaporation exerted a consistent positive influence whilst humidity and precipitation exerted a consistent negative influence on ground ozone concentrations in most cities. On the other hand, the influence direction of wind speed, wind direction and air pressure varied significantly. Based on multi-year comparison, meteorological influences on ground ozone concentrations were generally consistent, and soaring ozone concentrations across China in 2017 could be mainly attributed to the notable change of meteorological conditions in 2017, characterized with rising temperature and SSD and decreasing humidity. Consequently, meteorological means such as wind-corridors and artificial precipitation can be a promising approach for mitigating seasonal and short-term ozone pollution.
•Temperature, humidity and SSD exerted a major influence on ground ozone concentrations.•Temperature was the most influential factor for ground ozone concentrations.•The influence direction of wind speed, wind direction and air pressure varied significantly.•Soaring ozone concentrations in 2017 resulted from favorable meteorological conditions.•Meteorological means should be considered for mitigating composite air pollution.
Outdoor air pollution adversely affects human health and is estimated to be responsible for five to ten per cent of the total annual premature mortality in the contiguous United States
. Combustion ...emissions from a variety of sources, such as power generation or road traffic, make a large contribution to harmful air pollutants such as ozone and fine particulate matter (PM
)
. Efforts to mitigate air pollution have focused mainly on the relationship between local emission sources and local air quality
. Air quality can also be affected by distant emission sources, however, including emissions from neighbouring federal states
. This cross-state exchange of pollution poses additional regulatory challenges. Here we quantify the exchange of air pollution among the contiguous United States, and assess its impact on premature mortality that is linked to increased human exposure to PM
and ozone from seven emission sectors for 2005 to 2018. On average, we find that 41 to 53 per cent of air-quality-related premature mortality resulting from a state's emissions occurs outside that state. We also find variations in the cross-state contributions of different emission sectors and chemical species to premature mortality, and changes in these variations over time. Emissions from electric power generation have the greatest cross-state impacts as a fraction of their total impacts, whereas commercial/residential emissions have the smallest. However, reductions in emissions from electric power generation since 2005 have meant that, by 2018, cross-state premature mortality associated with the commercial/residential sector was twice that associated with power generation. In terms of the chemical species emitted, nitrogen oxides and sulfur dioxide emissions caused the most cross-state premature deaths in 2005, but by 2018 primary PM
emissions led to cross-state premature deaths equal to three times those associated with sulfur dioxide emissions. These reported shifts in emission sectors and emission species that contribute to premature mortality may help to guide improvements to air quality in the contiguous United States.
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