There are a limited number of studies on the estimation of environmental Kuznets curve (EKC) hypothesis for nitrous oxide (N₂O) emissions, though it is one of the most harmful greenhouse gases (GHGs) present in ambient atmosphere. In the wake of industrialization, it is necessary to understand the impact of energy consumption pattern on N₂O emissions and revise the energy policies accordingly. In this study, we have analyzed the impact of renewable and fossil fuel energy consumptions on N₂O emissions for APEC countries over the period of 1990–2015, and the analysis has been carried out following the EKC hypothesis framework. The results obtained from the study indicate the efficacy of the renewable energy solutions in having positive impact on environmental quality by helping to reduce the level of N₂O emissions. The policy implications derived from the results are designed while keeping the objectives of sustainable development goals (SDGs) in mind, so that the energy policies can bring forth sustainability in the economic systems in these nations.

Given that the volume of carbon emissions in the US is a significant share of the global greenhouse gas emissions, some salient factors are being currently examined so as to reverse the threat to global environmental sustainability. To this regard, the current study investigates the co-movement and long-term and short-term causal relationship between CO₂ emission (a proxy for environmental quality) and renewable consumption, immigration, and healthcare by using the wavelet coherence approach which primarily provides information on dynamic correlations over time and for different time scales. The coherence approach allows the one-dimensional time data into the bi-dimensional time-frequency sphere between the variables. In addition to investigating the causal relationship between CO₂ and renewable consumption, immigration, and healthcare, this study also employs gradual-shift causality and Toda-Yamamoto causality tests. With this, the study found a high variation for CO₂ emission in the US at 8 scales (8 quarters) from 1999 to 2008. Additionally, there is significant feedback causality between CO₂ emission and renewable consumption at different scales while a positive correlation between the variables is observed in the short run. Similarly, the result reveals that immigration significantly causes CO₂ emission in the US from 2008 to 2010 and a two-way causality is detected between CO₂ emission and healthcare at different frequencies and time period. Moreover, the Toda-Yamamoto causality and gradual-shift causality tests provide supportive evidence to the outcomes of the wavelet coherence–based causality test in this study. Overall, the investigation offers significant policy directive especially toward addressing the potential adverse effects from the country’s immigration and healthcare amendments.

This study aims to investigate the relationship between carbon dioxide (CO₂) emissions, macroeconomic instability, real output (GDP), the square of real output (GDP²), and financial development in Pakistan using the annual dataset over the period 1971–2016. The long-run analysis is based on the ARDL bound testing approach to cointegration, whereas the short-run dynamics are observed using error correction model. The results of the bound testing approach indicate that there exists a long-run relationship between the selected variables and macroeconomic instability increases pollution emissions. In addition, the study supports the presence of environmental Kuznets curve (EKC) hypothesis for Pakistan economy where, in low-income regime, an increase in GDP causes more emissions and, in high-income regime, the relationship between GDP and CO₂ emissions becomes negative. Finally, financial development variables exert a positive impact on environmental degradation. Based on these findings, our study supports a strong role of macroeconomic stability in achieving the targets of pollution reductions.

The profound appreciation of urban expansion and land use change (LUC) considerably influences the ecosystem functions, services, and biodiversity along with the local and regional climate. Land use has undergone an awful transformation due to rapid urbanization and population growth, which in turn increased land surface temperature (LST) in district Peshawar, Pakistan. The current study tends to capture the influence of land use on LST and agricultural productivity by employing multi-temporal, multispectral satellite data and agricultural production data during the selected years, i.e., 1996, 2003, and 2016. The results demonstrated that barren land considerably decreased while the urban area increased over time in all three phases. Furthermore, significant LST difference was found in different land cover units; e.g., barren land and urban area have the maximum, while water bodies followed by vegetation retain minimum LST in all three phases, i.e., 1996, 2003, and 2016. Similarly, the results from agricultural production revealed that except for wheat crops, which decreased by 7.54% during 1999–2003, the production of all major food crops increased during the selected years. However, the production of sugar cane and barley experienced considerable reduction during the selected years, except for barley, which increased by 22.86% during 2003–2016. The finding of this study provides guidance, policy recommendations, and reference for future researchers. Graphical abstract .

The consumption trend of nanoparticles by industry in this moment pays attention to titanium nanoparticles (TiNPs), due to their various applications: personal care products, household products, food industry, electronic devices, and healthcare products. Rising consumption of TiNPs without specific regulatory criteria for control safety releasing quantification leads to concern on the topic of environmental contamination and injurious effect. Therefore, this study investigates TiNP toxicities on aquatic animals representing hazardous effects to natural water resource, by determining 24-h LC₅₀ of TiNPs with histopathology investigation. We select brine shrimp (Artemia salina) as a model. Ten adults A. salina were incubated at room temperature for 24 h with various concentrations of TiNPs in triplicate. The mortality number of A. salina was recorded and LC₅₀ value was calculated. The LC₅₀ result is 1693.43 mg/L. Next, A. salina histopathology investigation was done by selecting the living ones after incubation for 24 h with 25% LC₅₀ of TiNPs. We performed tissue processing, embedding, sectioning, and H&E staining, and observed under light microscope. Histopathology reveals TiNP occlusion throughout the intestinal tract. Epithelial cells show abnormal morphology such as hyperplasia, villus deformation, disorganized arrangement, severe edema, and necrosis area. Consequently, the current study shows the severity of TiNP effects on aquatic microcrustaceans and their negative impact on the ecosystem. Furthermore, this information will aid the elucidation of TiNP toxicity effect and the risk of ecosystem disruptions.

Gaseous fuel as a combustion enhancer with a pilot fuel offers significant benefits in improving engine efficiency. Hydrogen and hydroxy are the two most common gaseous fuels that have been widely investigated in the CI engine but which one performs best is still inconvenient. In this study, hydrogen and hydroxy were injected with BD40 (v/v) separately in a common diesel engine to compare the performance and emission characteristics of these fuels. Engine performance parameters include brake thermal efficiency (BTE) and brake-specific energy consumption (BSEC), and exhaust emissions include hydrocarbon (HC), CO, CO₂, NOx, and smoke opacity. The induction of both hydroxy and hydrogen with BD40 has a positive effect on engine performance and emissions except NOx when compared to neat diesel fuel and BD40. The BTE of hydroxy-rich BD40 increased by 7.2% while BSEC reduced by 7.6% as compared to BD40 with hydrogen. The CO, HC, and smoke opacity of hydroxy-operated engine was found to be better than hydrogen-inducted engine. The NOx emission increased with the induction of both gaseous fuels and hydroxy-enriched BD40 produced 12.5% more emission than hydrogen-operated BD40 engine. Thus, more concisely, hydroxy-operated biodiesel engine performed better than hydrogen engine in terms of BTE, BSEC, CO, HC, and smoke opacity.

Traditional composting processes must be conducted with a bulking agent to ensure adequate air space for aeration. The bulking agent and composting materials are always completely mixed. A novel layered structure was introduced in sewage sludge composting, in which no bulking agent was used and bamboo charcoal was used as a separating material. Three lab-scale composting reactors (A: sawdust and sludge; B: bamboo charcoal and sludge; and C: sawdust, bamboo charcoal, and sludge) were continuously operated for 29 days. Several physicochemical parameters were investigated to evaluate the feasibility of layered composting with bamboo charcoal. The results indicated that the maximum temperatures during the thermophilic stage in treatments A, B, and C were 51.4, 50.9, and 51 °C, respectively. Layered composting with bamboo charcoal decreased the pH of the thermophilic stage from 8.98 in A to 8.75 in C, and delayed the peaks by about 120 h. The degradation rates of dissolve organic carbon (DOC) and dissolved nitrogen (DN) were 75 and 71.5% in treatment B, respectively, which were significantly higher than those of control group A (60 and 59.1%, respectively). The total NH₃ emissions of treatment C (2127.8 mg) were significantly lower than those of A (2522.8 mg). Our results suggested that layered composting using bamboo charcoal as a separating material could be an alternative strategy to the traditional composting method. Moreover, layered composting combined with sawdust could effectively reduce NH₃ emissions and N loss.

The electrochemical conversion of inorganic nitrogen forms (i.e., NO₃⁻-N, NO₂⁻-N, and NH₄⁺-N) to N₂ was studied using Ti as cathode and Ti/PbO₂ as anode in the simulated wastewater. According to linear sweep voltammetry, nitric nitrogen was effectively converted to N₂ on Ti cathode at the working potential more negative than − 1.1 V (vs. SCE). Ti/PbO₂ anode had the working potential of + 0.8 V (vs. SCE) for NH₄⁺-N converted to N₂. The apparent rate constants of NO₃⁻-N to NO₂⁻-N and NO₂⁻-N to N₂ were 2.46 × 10⁻² min⁻¹ and 4.03 × 10⁻² min⁻¹, respectively. The kinetic analyses revealed that the reduction of NO₃⁻-N was a two-step process, and NO₂⁻-N was an unstable intermediate, which could be easily oxidized to NO₃⁻-N or reduced to NH₄⁺-N. The majority of NH₄⁺-N could be effectively converted to N₂ on Ti/PbO₂ anode with the apparent rate constants of 5.12 × 10⁻² min⁻¹. The dual-chamber (DC) reactor with circulation was used in the batch electrolysis of simulated and actual wastewater. The results verified the pathways of NH₄⁺-N oxidation and NO₃⁻-N reduction and achieved high conversion rate of total nitrogen (TN) to N₂.

Acceleration of environmental degradation in recent years highlights the environmental quality as an indication of welfare and increases the number of studies conducted within this framework. Also, economic decision-making units have been doing various spending in order to maintain/increase environmental quality. In this context, the aim of this study is to examine the effect of environmental expenditures made by public sector on ecological deficit as a representative of the environmental quality for 9 coordinated market economies in Europe from 1995 to 2014. According to the findings acquired in the research, a cointegration relationship has been found between variables. It has been detected within the frame of panel ARDL analysis that total public expenditures increase the ecological deficit while environmental expenditures decrease it. In other words, scale effect of public expenditures affects the environmental quality negatively but its composition effect which will take place in favour of environmental expenditures has a positive effect. Thus, instead of the size of public expenditures, focusing on how the content of public expenditures of policy makers is formed in a way highlighting the environmental expenditures can boost welfare over environmental quality.